diff --git a/include/swift/AST/DiagnosticsClangImporter.def b/include/swift/AST/DiagnosticsClangImporter.def
index 600709b3f2805..288f23b9d4c5d 100644
--- a/include/swift/AST/DiagnosticsClangImporter.def
+++ b/include/swift/AST/DiagnosticsClangImporter.def
@@ -42,6 +42,8 @@ WARNING(could_not_rewrite_bridging_header,none,
 ERROR(bridging_header_pch_error,Fatal,
    "failed to emit precompiled header '%0' for bridging header '%1'",
    (StringRef, StringRef))
+ERROR(err_rewrite_bridging_header,none,
+  "failed to serialize bridging header: '%0'", (StringRef))
 
 ERROR(emit_pcm_error,Fatal,
    "failed to emit precompiled module '%0' for module map '%1'",
diff --git a/include/swift/AST/DiagnosticsSema.def b/include/swift/AST/DiagnosticsSema.def
index 2905dcdd2d2ed..94006af84f9e5 100644
--- a/include/swift/AST/DiagnosticsSema.def
+++ b/include/swift/AST/DiagnosticsSema.def
@@ -1193,6 +1193,9 @@ REMARK(module_api_import_aliases,none,
        "%select{, which reexports definition from %2|}3",
        (const Decl *, ModuleDecl *, ModuleDecl *, bool))
 
+REMARK(skip_module_invalid,none,"skip invalid swiftmodule: %0", (StringRef))
+REMARK(skip_module_testable,none,"skip swiftmodule built with '-enable-testing': %0", (StringRef))
+
 REMARK(macro_loaded,none,
        "loaded macro implementation module %0 from "
        "%select{shared library '%2'|executable '%2'|"
diff --git a/include/swift/AST/ModuleDependencies.h b/include/swift/AST/ModuleDependencies.h
index a20807d09c081..c3d6bae702397 100644
--- a/include/swift/AST/ModuleDependencies.h
+++ b/include/swift/AST/ModuleDependencies.h
@@ -1097,6 +1097,12 @@ class ModuleDependenciesCache {
   std::optional<const ModuleDependencyInfo *>
   findDependency(StringRef moduleName) const;
 
+  /// Look for known existing dependencies.
+  ///
+  /// \returns the cached result.
+  const ModuleDependencyInfo &
+  findKnownDependency(const ModuleDependencyID &moduleID) const;
+
   /// Record dependencies for the given module.
   void recordDependency(StringRef moduleName,
                         ModuleDependencyInfo dependencies);
diff --git a/include/swift/AST/SearchPathOptions.h b/include/swift/AST/SearchPathOptions.h
index 14ed706c67a95..dd7debcce1351 100644
--- a/include/swift/AST/SearchPathOptions.h
+++ b/include/swift/AST/SearchPathOptions.h
@@ -38,6 +38,15 @@ enum class ModuleSearchPathKind {
   RuntimeLibrary,
 };
 
+/// Specifies how to load modules when both a module interface and serialized
+/// AST are present, or whether to disallow one format or the other altogether.
+enum class ModuleLoadingMode {
+  PreferInterface,
+  PreferSerialized,
+  OnlyInterface,
+  OnlySerialized
+};
+
 /// A single module search path that can come from different sources, e.g.
 /// framework search paths, import search path etc.
 class ModuleSearchPath : public llvm::RefCountedBase<ModuleSearchPath> {
@@ -499,6 +508,12 @@ class SearchPathOptions {
   /// original form.
   PathObfuscator DeserializedPathRecoverer;
 
+  /// Specify the module loading behavior of the compilation.
+  ModuleLoadingMode ModuleLoadMode = ModuleLoadingMode::PreferSerialized;
+
+  /// Legacy scanner search behavior.
+  bool NoScannerModuleValidation = false;
+
   /// Return all module search paths that (non-recursively) contain a file whose
   /// name is in \p Filenames.
   SmallVector<const ModuleSearchPath *, 4>
@@ -546,7 +561,9 @@ class SearchPathOptions {
                         RuntimeResourcePath,
                         hash_combine_range(RuntimeLibraryImportPaths.begin(),
                                            RuntimeLibraryImportPaths.end()),
-                        DisableModulesValidateSystemDependencies);
+                        DisableModulesValidateSystemDependencies,
+                        NoScannerModuleValidation,
+                        ModuleLoadMode);
   }
 
   /// Return a hash code of any components from these options that should
diff --git a/include/swift/ClangImporter/ClangImporter.h b/include/swift/ClangImporter/ClangImporter.h
index e5fc22588da83..01d6415d525d1 100644
--- a/include/swift/ClangImporter/ClangImporter.h
+++ b/include/swift/ClangImporter/ClangImporter.h
@@ -402,8 +402,10 @@ class ClangImporter final : public ClangModuleLoader {
   getWrapperForModule(const clang::Module *mod,
                       bool returnOverlayIfPossible = false) const override;
 
-  std::string getBridgingHeaderContents(StringRef headerPath, off_t &fileSize,
-                                        time_t &fileModTime);
+  std::string
+  getBridgingHeaderContents(StringRef headerPath, off_t &fileSize,
+                            time_t &fileModTime,
+                            StringRef pchIncludeTree);
 
   /// Makes a temporary replica of the ClangImporter's CompilerInstance, reads
   /// an Objective-C header file into the replica and emits a PCH file of its
diff --git a/include/swift/Option/FrontendOptions.td b/include/swift/Option/FrontendOptions.td
index f30e8b1ede5a1..27098b7cd1a37 100644
--- a/include/swift/Option/FrontendOptions.td
+++ b/include/swift/Option/FrontendOptions.td
@@ -1337,4 +1337,10 @@ def disable_strict_concurrency_region_based_isolation : Flag<["-"],
   HelpText<"Disable region based isolation when running with strict concurrency enabled. Only enabled with asserts">,
   Flags<[HelpHidden]>;
 
+def no_scanner_module_validation: Flag<["-"], "no-scanner-module-validation">,
+    HelpText<"Do not validate binary modules in scanner and delegate the validation to swift-frontend">;
+def module_load_mode: Separate<["-"], "module-load-mode">,
+    MetaVarName<"only-interface|prefer-interface|prefer-serialized|only-serialized">,
+    HelpText<"Module loading mode">;
+
 } // end let Flags = [FrontendOption, NoDriverOption, HelpHidden]
diff --git a/include/swift/Serialization/ScanningLoaders.h b/include/swift/Serialization/ScanningLoaders.h
index 12698ce2af8ce..d3419e1269233 100644
--- a/include/swift/Serialization/ScanningLoaders.h
+++ b/include/swift/Serialization/ScanningLoaders.h
@@ -34,7 +34,8 @@ class SwiftModuleScanner : public SerializedModuleLoaderBase {
 
   /// Scan the given interface file to determine dependencies.
   llvm::ErrorOr<ModuleDependencyInfo>
-  scanInterfaceFile(Twine moduleInterfacePath, bool isFramework);
+  scanInterfaceFile(Twine moduleInterfacePath, bool isFramework,
+                    bool isTestableImport);
 
   InterfaceSubContextDelegate &astDelegate;
 
diff --git a/include/swift/Serialization/SerializedModuleLoader.h b/include/swift/Serialization/SerializedModuleLoader.h
index a51f85d918c8c..8e32a130a7979 100644
--- a/include/swift/Serialization/SerializedModuleLoader.h
+++ b/include/swift/Serialization/SerializedModuleLoader.h
@@ -16,6 +16,7 @@
 #include "swift/AST/FileUnit.h"
 #include "swift/AST/Module.h"
 #include "swift/AST/ModuleLoader.h"
+#include "swift/AST/SearchPathOptions.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/PrefixMapper.h"
 #include "llvm/TargetParser/Triple.h"
@@ -23,20 +24,12 @@
 namespace swift {
 class ModuleFile;
 class PathObfuscator;
+class ModuleFileSharedCore;
 enum class ModuleLoadingBehavior;
 namespace file_types {
   enum ID : uint8_t;
 }
 
-/// Specifies how to load modules when both a module interface and serialized
-/// AST are present, or whether to disallow one format or the other altogether.
-enum class ModuleLoadingMode {
-  PreferInterface,
-  PreferSerialized,
-  OnlyInterface,
-  OnlySerialized
-};
-
 /// How a dependency should be loaded.
 ///
 /// \sa getTransitiveLoadingBehavior
@@ -170,22 +163,18 @@ class SerializedModuleLoaderBase : public ModuleLoader {
   }
 
   /// Scan the given serialized module file to determine dependencies.
-  llvm::ErrorOr<ModuleDependencyInfo> scanModuleFile(Twine modulePath, bool isFramework);
+  llvm::ErrorOr<ModuleDependencyInfo>
+  scanModuleFile(Twine modulePath, bool isFramework, bool isTestableImport);
 
   struct BinaryModuleImports {
     llvm::StringSet<> moduleImports;
     std::string headerImport;
   };
 
-  static llvm::ErrorOr<BinaryModuleImports>
-  getImportsOfModule(Twine modulePath,
+  static BinaryModuleImports
+  getImportsOfModule(const ModuleFileSharedCore &loadedModule,
                      ModuleLoadingBehavior transitiveBehavior,
-                     bool isFramework,
-                     bool isRequiredOSSAModules,
-                     StringRef SDKName,
-                     StringRef packageName,
-                     llvm::vfs::FileSystem *fileSystem,
-                     PathObfuscator &recoverer);
+                     StringRef packageName, bool isTestableImport);
 
   /// Load the module file into a buffer and also collect its module name.
   static std::unique_ptr<llvm::MemoryBuffer>
diff --git a/lib/AST/ModuleDependencies.cpp b/lib/AST/ModuleDependencies.cpp
index 0a26a5bac8848..8f425281e69e5 100644
--- a/lib/AST/ModuleDependencies.cpp
+++ b/lib/AST/ModuleDependencies.cpp
@@ -21,6 +21,7 @@
 #include "swift/Frontend/Frontend.h"
 #include "llvm/CAS/CASProvidingFileSystem.h"
 #include "llvm/CAS/CachingOnDiskFileSystem.h"
+#include "llvm/Config/config.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/PrefixMapper.h"
@@ -480,6 +481,58 @@ void SwiftDependencyTracker::addCommonSearchPathDeps(
   // Add VFSOverlay file.
   for (auto &Overlay: Opts.VFSOverlayFiles)
     FS->status(Overlay);
+
+  // Add plugin dylibs from the toolchain only by look through the plugin search
+  // directory.
+  auto recordFiles = [&](StringRef Path) {
+    std::error_code EC;
+    for (auto I = FS->dir_begin(Path, EC);
+         !EC && I != llvm::vfs::directory_iterator(); I = I.increment(EC)) {
+      if (I->type() != llvm::sys::fs::file_type::regular_file)
+        continue;
+#if defined(_WIN32)
+      constexpr StringRef libPrefix{};
+      constexpr StringRef libSuffix = ".dll";
+#else
+      constexpr StringRef libPrefix = "lib";
+      constexpr StringRef libSuffix = LTDL_SHLIB_EXT;
+#endif
+      StringRef filename = llvm::sys::path::filename(I->path());
+      if (filename.starts_with(libPrefix) && filename.ends_with(libSuffix))
+        FS->status(I->path());
+    }
+  };
+  for (auto &entry : Opts.PluginSearchOpts) {
+    switch (entry.getKind()) {
+
+    // '-load-plugin-library <library path>'.
+    case PluginSearchOption::Kind::LoadPluginLibrary: {
+      auto &val = entry.get<PluginSearchOption::LoadPluginLibrary>();
+      FS->status(val.LibraryPath);
+      break;
+    }
+
+    // '-load-plugin-executable <executable path>#<module name>, ...'.
+    case PluginSearchOption::Kind::LoadPluginExecutable: {
+      // We don't have executable plugin in toolchain.
+      break;
+    }
+
+    // '-plugin-path <library search path>'.
+    case PluginSearchOption::Kind::PluginPath: {
+      auto &val = entry.get<PluginSearchOption::PluginPath>();
+      recordFiles(val.SearchPath);
+      break;
+    }
+
+    // '-external-plugin-path <library search path>#<server path>'.
+    case PluginSearchOption::Kind::ExternalPluginPath: {
+      auto &val = entry.get<PluginSearchOption::ExternalPluginPath>();
+      recordFiles(val.SearchPath);
+      break;
+    }
+    }
+  }
 }
 
 void SwiftDependencyTracker::startTracking() {
@@ -739,6 +792,13 @@ ModuleDependenciesCache::findDependency(StringRef moduleName) const {
   return std::nullopt;
 }
 
+const ModuleDependencyInfo &ModuleDependenciesCache::findKnownDependency(
+    const ModuleDependencyID &moduleID) const {
+  auto dep = findDependency(moduleID);
+  assert(dep && "dependency unknown");
+  return **dep;
+}
+
 bool ModuleDependenciesCache::hasDependency(const ModuleDependencyID &moduleID) const {
   return hasDependency(moduleID.ModuleName, moduleID.Kind);
 }
diff --git a/lib/AST/PluginLoader.cpp b/lib/AST/PluginLoader.cpp
index 658b28348e1d4..95f1b01ed24a8 100644
--- a/lib/AST/PluginLoader.cpp
+++ b/lib/AST/PluginLoader.cpp
@@ -17,6 +17,7 @@
 #include "swift/Basic/SourceManager.h"
 #include "swift/Parse/Lexer.h"
 #include "llvm/Config/config.h"
+#include "llvm/Support/VirtualFileSystem.h"
 
 using namespace swift;
 
@@ -59,6 +60,15 @@ static StringRef pluginModuleNameStringFromPath(StringRef path) {
   return "";
 }
 
+static llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem>
+getPluginLoadingFS(ASTContext &Ctx) {
+  // If there is a clang include tree FS, using real file system to load plugin
+  // as the FS in SourceMgr doesn't support directory iterator.
+  if (Ctx.ClangImporterOpts.HasClangIncludeTreeRoot)
+    return llvm::vfs::getRealFileSystem();
+  return Ctx.SourceMgr.getFileSystem();
+}
+
 llvm::DenseMap<Identifier, PluginLoader::PluginEntry> &
 PluginLoader::getPluginMap() {
   if (PluginMap.has_value()) {
@@ -86,7 +96,7 @@ PluginLoader::getPluginMap() {
     (void)result;
   };
 
-  auto fs = Ctx.SourceMgr.getFileSystem();
+  auto fs = getPluginLoadingFS(Ctx);
   std::error_code ec;
 
   for (auto &entry : Ctx.SearchPathOpts.PluginSearchOpts) {
@@ -162,7 +172,7 @@ PluginLoader::lookupPluginByModuleName(Identifier moduleName) {
 
 llvm::Expected<LoadedLibraryPlugin *>
 PluginLoader::loadLibraryPlugin(StringRef path) {
-  auto fs = Ctx.SourceMgr.getFileSystem();
+  auto fs = getPluginLoadingFS(Ctx);
   SmallString<128> resolvedPath;
   if (auto err = fs->getRealPath(path, resolvedPath)) {
     return llvm::createStringError(err, err.message());
@@ -186,7 +196,7 @@ PluginLoader::loadLibraryPlugin(StringRef path) {
 
 llvm::Expected<LoadedExecutablePlugin *>
 PluginLoader::loadExecutablePlugin(StringRef path) {
-  auto fs = Ctx.SourceMgr.getFileSystem();
+  auto fs = getPluginLoadingFS(Ctx);
   SmallString<128> resolvedPath;
   if (auto err = fs->getRealPath(path, resolvedPath)) {
     return llvm::createStringError(err, err.message());
diff --git a/lib/ClangImporter/ClangImporter.cpp b/lib/ClangImporter/ClangImporter.cpp
index a9b15c6871231..ec580ce31c305 100644
--- a/lib/ClangImporter/ClangImporter.cpp
+++ b/lib/ClangImporter/ClangImporter.cpp
@@ -55,13 +55,16 @@
 #include "clang/Basic/DiagnosticOptions.h"
 #include "clang/Basic/FileEntry.h"
 #include "clang/Basic/IdentifierTable.h"
+#include "clang/Basic/LangStandard.h"
 #include "clang/Basic/Module.h"
 #include "clang/Basic/TargetInfo.h"
 #include "clang/Basic/Version.h"
 #include "clang/CAS/CASOptions.h"
+#include "clang/CAS/IncludeTree.h"
 #include "clang/CodeGen/ObjectFilePCHContainerOperations.h"
 #include "clang/Frontend/CompilerInvocation.h"
 #include "clang/Frontend/FrontendActions.h"
+#include "clang/Frontend/IncludeTreePPActions.h"
 #include "clang/Frontend/TextDiagnosticPrinter.h"
 #include "clang/Frontend/Utils.h"
 #include "clang/Index/IndexingAction.h"
@@ -80,7 +83,11 @@
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringExtras.h"
+#include "llvm/CAS/CASReference.h"
+#include "llvm/CAS/ObjectStore.h"
 #include "llvm/Support/CrashRecoveryContext.h"
+#include "llvm/Support/Error.h"
+#include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/FileCollector.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Memory.h"
@@ -1696,8 +1703,13 @@ bool ClangImporter::importHeader(StringRef header, ModuleDecl *adapter,
                                  StringRef cachedContents, SourceLoc diagLoc) {
   clang::FileManager &fileManager = Impl.Instance->getFileManager();
   auto headerFile = fileManager.getFile(header, /*OpenFile=*/true);
+  // Prefer importing the header directly if the header content matches by
+  // checking size and mod time. This allows correct import if some no-modular
+  // headers are already imported into clang importer. If mod time is zero, then
+  // the module should be built from CAS and there is no mod time to verify.
   if (headerFile && (*headerFile)->getSize() == expectedSize &&
-      (*headerFile)->getModificationTime() == expectedModTime) {
+      (expectedModTime == 0 ||
+       (*headerFile)->getModificationTime() == expectedModTime)) {
     return importBridgingHeader(header, adapter, diagLoc, false, true);
   }
 
@@ -1752,16 +1764,46 @@ bool ClangImporter::importBridgingHeader(StringRef header, ModuleDecl *adapter,
                            std::move(sourceBuffer), implicitImport);
 }
 
-std::string ClangImporter::getBridgingHeaderContents(StringRef headerPath,
-                                                     off_t &fileSize,
-                                                     time_t &fileModTime) {
+static llvm::Expected<llvm::cas::ObjectRef>
+setupIncludeTreeInput(clang::CompilerInvocation &invocation,
+                      StringRef headerPath, StringRef pchIncludeTree) {
+  auto DB = invocation.getCASOpts().getOrCreateDatabases();
+  if (!DB)
+    return DB.takeError();
+  auto CAS = DB->first;
+  auto ID = CAS->parseID(pchIncludeTree);
+  if (!ID)
+    return ID.takeError();
+  auto includeTreeRef = CAS->getReference(*ID);
+  if (!includeTreeRef)
+    return llvm::cas::ObjectStore::createUnknownObjectError(*ID);
+
+  invocation.getFrontendOpts().Inputs.push_back(clang::FrontendInputFile(
+      *includeTreeRef, headerPath, clang::Language::ObjC));
+
+  return *includeTreeRef;
+}
+
+std::string ClangImporter::getBridgingHeaderContents(
+    StringRef headerPath, off_t &fileSize, time_t &fileModTime,
+    StringRef pchIncludeTree) {
   auto invocation =
       std::make_shared<clang::CompilerInvocation>(*Impl.Invocation);
 
   invocation->getFrontendOpts().DisableFree = false;
   invocation->getFrontendOpts().Inputs.clear();
-  invocation->getFrontendOpts().Inputs.push_back(
-      clang::FrontendInputFile(headerPath, clang::Language::ObjC));
+
+  std::optional<llvm::cas::ObjectRef> includeTreeRef;
+  if (pchIncludeTree.empty())
+    invocation->getFrontendOpts().Inputs.push_back(
+        clang::FrontendInputFile(headerPath, clang::Language::ObjC));
+  else if (auto err =
+               setupIncludeTreeInput(*invocation, headerPath, pchIncludeTree)
+                   .moveInto(includeTreeRef)) {
+    Impl.diagnose({}, diag::err_rewrite_bridging_header,
+                  toString(std::move(err)));
+    return "";
+  }
 
   invocation->getPreprocessorOpts().resetNonModularOptions();
 
@@ -1782,18 +1824,36 @@ std::string ClangImporter::getBridgingHeaderContents(StringRef headerPath,
     // write to an in-memory buffer.
     class RewriteIncludesAction : public clang::PreprocessorFrontendAction {
       raw_ostream &OS;
+      std::optional<llvm::cas::ObjectRef> includeTreeRef;
 
       void ExecuteAction() override {
         clang::CompilerInstance &compiler = getCompilerInstance();
+        // If the input is include tree, setup the IncludeTreePPAction.
+        if (includeTreeRef) {
+          auto IncludeTreeRoot = clang::cas::IncludeTreeRoot::get(
+              compiler.getOrCreateObjectStore(), *includeTreeRef);
+          if (!IncludeTreeRoot)
+            llvm::report_fatal_error(IncludeTreeRoot.takeError());
+          auto PPCachedAct =
+              clang::createPPActionsFromIncludeTree(*IncludeTreeRoot);
+          if (!PPCachedAct)
+            llvm::report_fatal_error(PPCachedAct.takeError());
+          compiler.getPreprocessor().setPPCachedActions(
+              std::move(*PPCachedAct));
+        }
+
         clang::RewriteIncludesInInput(compiler.getPreprocessor(), &OS,
                                       compiler.getPreprocessorOutputOpts());
       }
+
     public:
-      explicit RewriteIncludesAction(raw_ostream &os) : OS(os) {}
+      explicit RewriteIncludesAction(
+          raw_ostream &os, std::optional<llvm::cas::ObjectRef> includeTree)
+          : OS(os), includeTreeRef(includeTree) {}
     };
 
     llvm::raw_string_ostream os(result);
-    RewriteIncludesAction action(os);
+    RewriteIncludesAction action(os, includeTreeRef);
     rewriteInstance.ExecuteAction(action);
   });
 
@@ -2514,6 +2574,7 @@ ClangImporter::Implementation::Implementation(
           !ctx.ClangImporterOpts.BridgingHeader.empty()),
       DisableOverlayModules(ctx.ClangImporterOpts.DisableOverlayModules),
       EnableClangSPI(ctx.ClangImporterOpts.EnableClangSPI),
+      UseClangIncludeTree(ctx.ClangImporterOpts.UseClangIncludeTree),
       importSymbolicCXXDecls(
           ctx.LangOpts.hasFeature(Feature::ImportSymbolicCXXDecls)),
       IsReadingBridgingPCH(false),
diff --git a/lib/ClangImporter/ImporterImpl.h b/lib/ClangImporter/ImporterImpl.h
index c31d51f4279d4..094b06e7aa02e 100644
--- a/lib/ClangImporter/ImporterImpl.h
+++ b/lib/ClangImporter/ImporterImpl.h
@@ -467,6 +467,7 @@ class LLVM_LIBRARY_VISIBILITY ClangImporter::Implementation
   const bool BridgingHeaderExplicitlyRequested;
   const bool DisableOverlayModules;
   const bool EnableClangSPI;
+  const bool UseClangIncludeTree;
   bool importSymbolicCXXDecls;
 
   bool IsReadingBridgingPCH;
diff --git a/lib/DependencyScan/ModuleDependencyScanner.cpp b/lib/DependencyScan/ModuleDependencyScanner.cpp
index 9c953020f8481..402e6cf651142 100644
--- a/lib/DependencyScan/ModuleDependencyScanner.cpp
+++ b/lib/DependencyScan/ModuleDependencyScanner.cpp
@@ -185,7 +185,8 @@ ModuleDependencyScanningWorker::ModuleDependencyScanningWorker(
       ScanASTContext,
       *static_cast<ModuleInterfaceCheckerImpl *>(
           ScanASTContext.getModuleInterfaceChecker()),
-      &DependencyTracker, ModuleLoadingMode::OnlyInterface);
+      &DependencyTracker,
+      ScanCompilerInvocation.getSearchPathOptions().ModuleLoadMode);
 }
 
 ModuleDependencyVector
diff --git a/lib/DependencyScan/ScanDependencies.cpp b/lib/DependencyScan/ScanDependencies.cpp
index 841c4d12b257e..f8f6c3c0f082e 100644
--- a/lib/DependencyScan/ScanDependencies.cpp
+++ b/lib/DependencyScan/ScanDependencies.cpp
@@ -192,7 +192,7 @@ updateModuleCacheKey(ModuleDependencyInfo &depInfo,
 }
 
 static llvm::Error resolveExplicitModuleInputs(
-    ModuleDependencyID moduleID, const ModuleDependencyInfo &resolvingDepInfo,
+    ModuleDependencyID moduleID,
     const std::set<ModuleDependencyID> &dependencies,
     ModuleDependenciesCache &cache, CompilerInstance &instance,
     std::optional<std::set<ModuleDependencyID>> bridgingHeaderDeps) {
@@ -200,6 +200,7 @@ static llvm::Error resolveExplicitModuleInputs(
   if (moduleID.Kind == ModuleDependencyKind::SwiftPlaceholder)
     return llvm::Error::success();
 
+  auto &resolvingDepInfo = cache.findKnownDependency(moduleID);
   // If the dependency is already finalized, nothing needs to be done.
   if (resolvingDepInfo.isFinalized())
     return llvm::Error::success();
@@ -242,13 +243,10 @@ static llvm::Error resolveExplicitModuleInputs(
 
   std::vector<std::string> commandLine = resolvingDepInfo.getCommandline();
   for (const auto &depModuleID : dependencies) {
-    const auto optionalDepInfo =
-        cache.findDependency(depModuleID);
-    assert(optionalDepInfo.has_value());
-    const auto depInfo = optionalDepInfo.value();
+    const auto &depInfo = cache.findKnownDependency(depModuleID);
     switch (depModuleID.Kind) {
     case swift::ModuleDependencyKind::SwiftInterface: {
-      auto interfaceDepDetails = depInfo->getAsSwiftInterfaceModule();
+      auto interfaceDepDetails = depInfo.getAsSwiftInterfaceModule();
       assert(interfaceDepDetails && "Expected Swift Interface dependency.");
       auto &path = interfaceDepDetails->moduleCacheKey.empty()
                        ? interfaceDepDetails->moduleOutputPath
@@ -257,7 +255,7 @@ static llvm::Error resolveExplicitModuleInputs(
                             path);
     } break;
     case swift::ModuleDependencyKind::SwiftBinary: {
-      auto binaryDepDetails = depInfo->getAsSwiftBinaryModule();
+      auto binaryDepDetails = depInfo.getAsSwiftBinaryModule();
       assert(binaryDepDetails && "Expected Swift Binary Module dependency.");
       auto &path = binaryDepDetails->moduleCacheKey.empty()
                        ? binaryDepDetails->compiledModulePath
@@ -269,24 +267,23 @@ static llvm::Error resolveExplicitModuleInputs(
       // order to resolve the header's own header include directives.
       for (const auto &bridgingHeaderDepName :
            binaryDepDetails->headerModuleDependencies) {
-        auto optionalBridgingHeaderDepModuleInfo = cache.findDependency(
+        auto optionalBridgingHeaderDepModuleInfo = cache.findKnownDependency(
             {bridgingHeaderDepName, ModuleDependencyKind::Clang});
-        assert(optionalDepInfo.has_value());
         const auto bridgingHeaderDepModuleDetails =
-            optionalBridgingHeaderDepModuleInfo.value()->getAsClangModule();
+            optionalBridgingHeaderDepModuleInfo.getAsClangModule();
         commandLine.push_back(
             "-fmodule-map-file=" +
             remapPath(bridgingHeaderDepModuleDetails->moduleMapFile));
       }
     } break;
     case swift::ModuleDependencyKind::SwiftPlaceholder: {
-      auto placeholderDetails = depInfo->getAsPlaceholderDependencyModule();
+      auto placeholderDetails = depInfo.getAsPlaceholderDependencyModule();
       assert(placeholderDetails && "Expected Swift Placeholder dependency.");
       commandLine.push_back("-swift-module-file=" + depModuleID.ModuleName + "=" +
                             placeholderDetails->compiledModulePath);
     } break;
     case swift::ModuleDependencyKind::Clang: {
-      auto clangDepDetails = depInfo->getAsClangModule();
+      auto clangDepDetails = depInfo.getAsClangModule();
       assert(clangDepDetails && "Expected Clang Module dependency.");
       if (!resolvingDepInfo.isClangModule()) {
         commandLine.push_back("-Xcc");
@@ -303,13 +300,13 @@ static llvm::Error resolveExplicitModuleInputs(
       }
 
       // Only need to merge the CASFS from clang importer.
-      if (auto ID = depInfo->getCASFSRootID())
+      if (auto ID = depInfo.getCASFSRootID())
         rootIDs.push_back(*ID);
-      if (auto ID = depInfo->getClangIncludeTree())
+      if (auto ID = depInfo.getClangIncludeTree())
         includeTrees.push_back(*ID);
     } break;
     case swift::ModuleDependencyKind::SwiftSource: {
-      if (auto E = addBridgingHeaderDeps(*depInfo))
+      if (auto E = addBridgingHeaderDeps(depInfo))
         return E;
       break;
     }
@@ -390,9 +387,8 @@ static llvm::Error resolveExplicitModuleInputs(
       std::vector<std::string> newCommandLine =
           dependencyInfoCopy.getBridgingHeaderCommandline();
       for (auto bridgingDep : *bridgingHeaderDeps) {
-        auto dep = cache.findDependency(bridgingDep);
-        assert(dep && "unknown clang dependency");
-        auto *clangDep = (*dep)->getAsClangModule();
+        auto &dep = cache.findKnownDependency(bridgingDep);
+        auto *clangDep = dep.getAsClangModule();
         assert(clangDep && "wrong module dependency kind");
         if (!clangDep->moduleCacheKey.empty()) {
           newCommandLine.push_back("-Xcc");
@@ -406,19 +402,11 @@ static llvm::Error resolveExplicitModuleInputs(
       dependencyInfoCopy.updateBridgingHeaderCommandLine(newCommandLine);
     }
 
-    if (resolvingDepInfo.isClangModule() ||
-        resolvingDepInfo.isSwiftInterfaceModule()) {
-      // Compute and update module cache key.
-      auto Key = updateModuleCacheKey(dependencyInfoCopy, cache, CAS);
-      if (!Key)
-        return Key.takeError();
-    }
-
-    // For binary module, we need to make sure the lookup key is setup here in
-    // action cache. We just use the CASID of the binary module itself as key.
-    if (auto *binaryDep = dependencyInfoCopy.getAsSwiftBinaryModule()) {
-      auto Ref =
-          CASFS.getObjectRefForFileContent(binaryDep->compiledModulePath);
+    // Compute and update module cache key.
+    auto setupBinaryCacheKey = [&](StringRef path) -> llvm::Error {
+      // For binary module, we need to make sure the lookup key is setup here in
+      // action cache. We just use the CASID of the binary module itself as key.
+      auto Ref = CASFS.getObjectRefForFileContent(path);
       if (!Ref)
         return llvm::errorCodeToError(Ref.getError());
       assert(*Ref && "Binary module should be loaded into CASFS already");
@@ -432,18 +420,36 @@ static llvm::Error resolveExplicitModuleInputs(
       if (auto E = instance.getActionCache().put(CAS.getID(**Ref),
                                                  CAS.getID(*Result)))
         return E;
+      return llvm::Error::success();
+    };
+
+    if (resolvingDepInfo.isClangModule() ||
+        resolvingDepInfo.isSwiftInterfaceModule()) {
+      auto Key = updateModuleCacheKey(dependencyInfoCopy, cache, CAS);
+      if (!Key)
+        return Key.takeError();
+    } else if (auto *binaryDep = dependencyInfoCopy.getAsSwiftBinaryModule()) {
+      if (auto E = setupBinaryCacheKey(binaryDep->compiledModulePath))
+        return E;
     }
   }
+
   dependencyInfoCopy.setIsFinalized(true);
   cache.updateDependency(moduleID, dependencyInfoCopy);
 
   return llvm::Error::success();
 }
 
-static llvm::Error pruneUnusedVFSOverlays(
-    ModuleDependencyID moduleID, const ModuleDependencyInfo &resolvingDepInfo,
-    const std::set<ModuleDependencyID> &dependencies,
-    ModuleDependenciesCache &cache, CompilerInstance &instance) {
+static llvm::Error
+pruneUnusedVFSOverlays(ModuleDependencyID moduleID,
+                       const std::set<ModuleDependencyID> &dependencies,
+                       ModuleDependenciesCache &cache,
+                       CompilerInstance &instance) {
+  // Pruning of unused VFS overlay options for Clang dependencies
+  // is performed by the Clang dependency scanner.
+  if (moduleID.Kind == ModuleDependencyKind::Clang)
+    return llvm::Error::success();
+
   auto isVFSOverlayFlag = [](StringRef arg) {
     return arg == "-ivfsoverlay" || arg == "-vfsoverlay";
   };
@@ -451,11 +457,7 @@ static llvm::Error pruneUnusedVFSOverlays(
     return arg == "-Xcc";
   };
 
-  // Pruning of unused VFS overlay options for Clang dependencies
-  // is performed by the Clang dependency scanner.
-  if (!resolvingDepInfo.isSwiftModule())
-    return llvm::Error::success();
-
+  auto &resolvingDepInfo = cache.findKnownDependency(moduleID);
   // If this Swift dependency contains any VFS overlay paths,
   // then attempt to prune the ones not used by any of the Clang dependencies.
   if (!llvm::any_of(resolvingDepInfo.getCommandline(),
@@ -469,10 +471,8 @@ static llvm::Error pruneUnusedVFSOverlays(
   // pruned by the Clang dependency scanner.
   llvm::StringSet<> usedVFSOverlayPaths;
   for (const auto &depModuleID : dependencies) {
-    const auto optionalDepInfo = cache.findDependency(depModuleID);
-    assert(optionalDepInfo.has_value());
-    const auto depInfo = optionalDepInfo.value();
-    if (auto clangDepDetails = depInfo->getAsClangModule()) {
+    const auto &depInfo = cache.findKnownDependency(depModuleID);
+    if (auto clangDepDetails = depInfo.getAsClangModule()) {
       const auto &depCommandLine = clangDepDetails->buildCommandLine;
       // true if the previous argument was the dash-option of an option pair
       bool getNext = false;
@@ -1158,24 +1158,17 @@ generateFullDependencyGraph(const CompilerInstance &instance,
 
   for (size_t i = 0; i < allModules.size(); ++i) {
     const auto &module = allModules[i];
-    // Grab the completed module dependencies.
-    auto moduleDepsQuery = cache.findDependency(module);
-    if (!moduleDepsQuery) {
-      llvm::report_fatal_error(Twine("Module Dependency Cache missing module") +
-                               module.ModuleName);
-    }
-
-    auto moduleDeps = *moduleDepsQuery;
+    auto &moduleDeps = cache.findKnownDependency(module);
     // Collect all the required pieces to build a ModuleInfo
-    auto swiftPlaceholderDeps = moduleDeps->getAsPlaceholderDependencyModule();
-    auto swiftTextualDeps = moduleDeps->getAsSwiftInterfaceModule();
-    auto swiftSourceDeps = moduleDeps->getAsSwiftSourceModule();
-    auto swiftBinaryDeps = moduleDeps->getAsSwiftBinaryModule();
-    auto clangDeps = moduleDeps->getAsClangModule();
+    auto swiftPlaceholderDeps = moduleDeps.getAsPlaceholderDependencyModule();
+    auto swiftTextualDeps = moduleDeps.getAsSwiftInterfaceModule();
+    auto swiftSourceDeps = moduleDeps.getAsSwiftSourceModule();
+    auto swiftBinaryDeps = moduleDeps.getAsSwiftBinaryModule();
+    auto clangDeps = moduleDeps.getAsClangModule();
 
     // ModulePath
     const char *modulePathSuffix =
-        moduleDeps->isSwiftModule() ? ".swiftmodule" : ".pcm";
+        moduleDeps.isSwiftModule() ? ".swiftmodule" : ".pcm";
     std::string modulePath;
     if (swiftTextualDeps)
       modulePath = swiftTextualDeps->moduleOutputPath;
@@ -1196,10 +1189,8 @@ generateFullDependencyGraph(const CompilerInstance &instance,
       sourceFiles = clangDeps->fileDependencies;
     }
 
-    auto optionalDepInfo = cache.findDependency(module);
-    assert(optionalDepInfo.has_value() && "Missing dependency info during graph generation diagnosis.");
-    auto depInfo = optionalDepInfo.value();
-    auto directDependencies = depInfo->getDirectModuleDependencies();
+    auto &depInfo = cache.findKnownDependency(module);
+    auto directDependencies = depInfo.getDirectModuleDependencies();
 
     // Generate a swiftscan_clang_details_t object based on the dependency kind
     auto getModuleDetails = [&]() -> swiftscan_module_details_t {
@@ -1208,9 +1199,12 @@ generateFullDependencyGraph(const CompilerInstance &instance,
         swiftscan_string_ref_t moduleInterfacePath =
             create_clone(swiftTextualDeps->swiftInterfaceFile.c_str());
         swiftscan_string_ref_t bridgingHeaderPath =
-            swiftTextualDeps->textualModuleDetails.bridgingHeaderFile.has_value()
+            swiftTextualDeps->textualModuleDetails.bridgingHeaderFile
+                    .has_value()
                 ? create_clone(
-                      swiftTextualDeps->textualModuleDetails.bridgingHeaderFile.value().c_str())
+                      swiftTextualDeps->textualModuleDetails.bridgingHeaderFile
+                          .value()
+                          .c_str())
                 : create_null();
         details->kind = SWIFTSCAN_DEPENDENCY_INFO_SWIFT_TEXTUAL;
         // Create an overlay dependencies set according to the output format
@@ -1414,12 +1408,12 @@ computeTransitiveClosureOfExplicitDependencies(
 }
 
 static std::set<ModuleDependencyID> computeBridgingHeaderTransitiveDependencies(
-    const ModuleDependencyInfo *dep,
+    const ModuleDependencyInfo &dep,
     const std::unordered_map<ModuleDependencyID, std::set<ModuleDependencyID>>
         &transitiveClosures,
     const ModuleDependenciesCache &cache) {
   std::set<ModuleDependencyID> result;
-  auto *sourceDep = dep->getAsSwiftSourceModule();
+  auto *sourceDep = dep.getAsSwiftSourceModule();
   if (!sourceDep)
     return result;
 
@@ -1871,22 +1865,19 @@ static void resolveDependencyCommandLineArguments(
     // For main module or binary modules, no command-line to resolve.
     // For Clang modules, their dependencies are resolved by the clang Scanner
     // itself for us.
-    auto optionalDeps = cache.findDependency(modID);
-    assert(optionalDeps.has_value());
-    auto deps = optionalDeps.value();
+    auto &deps = cache.findKnownDependency(modID);
     std::optional<std::set<ModuleDependencyID>> bridgingHeaderDeps;
     if (modID.Kind == ModuleDependencyKind::SwiftSource)
       bridgingHeaderDeps = computeBridgingHeaderTransitiveDependencies(
           deps, moduleTransitiveClosures, cache);
 
-    if (auto E =
-            resolveExplicitModuleInputs(modID, *deps, dependencyClosure, cache,
-                                        instance, bridgingHeaderDeps))
+    if (auto E = resolveExplicitModuleInputs(modID, dependencyClosure, cache,
+                                             instance, bridgingHeaderDeps))
       instance.getDiags().diagnose(SourceLoc(), diag::error_cas,
                                    toString(std::move(E)));
 
-    if (auto E = pruneUnusedVFSOverlays(modID, *deps, dependencyClosure,
-                                        cache, instance))
+    if (auto E =
+            pruneUnusedVFSOverlays(modID, dependencyClosure, cache, instance))
       instance.getDiags().diagnose(SourceLoc(), diag::error_cas,
                                    toString(std::move(E)));
   }
diff --git a/lib/Frontend/CompilerInvocation.cpp b/lib/Frontend/CompilerInvocation.cpp
index b28976fb8dc17..3f990a386ee2c 100644
--- a/lib/Frontend/CompilerInvocation.cpp
+++ b/lib/Frontend/CompilerInvocation.cpp
@@ -1884,8 +1884,7 @@ static bool validateSwiftModuleFileArgumentAndAdd(const std::string &swiftModule
   return false;
 }
 
-static bool ParseSearchPathArgs(SearchPathOptions &Opts,
-                                ArgList &Args,
+static bool ParseSearchPathArgs(SearchPathOptions &Opts, ArgList &Args,
                                 DiagnosticEngine &Diags,
                                 StringRef workingDirectory) {
   using namespace options;
@@ -2020,6 +2019,31 @@ static bool ParseSearchPathArgs(SearchPathOptions &Opts,
   for (StringRef Opt : Args.getAllArgValues(OPT_scanner_prefix_map)) {
     Opts.ScannerPrefixMapper.push_back(Opt.str());
   }
+
+  Opts.NoScannerModuleValidation |=
+      Args.hasArg(OPT_no_scanner_module_validation);
+
+  std::optional<std::string> forceModuleLoadingMode;
+  if (auto *A = Args.getLastArg(OPT_module_load_mode))
+    forceModuleLoadingMode = A->getValue();
+  else if (auto Env = llvm::sys::Process::GetEnv("SWIFT_FORCE_MODULE_LOADING"))
+    forceModuleLoadingMode = Env;
+  if (forceModuleLoadingMode) {
+    if (*forceModuleLoadingMode == "prefer-interface" ||
+        *forceModuleLoadingMode == "prefer-parseable")
+      Opts.ModuleLoadMode = ModuleLoadingMode::PreferInterface;
+    else if (*forceModuleLoadingMode == "prefer-serialized")
+      Opts.ModuleLoadMode = ModuleLoadingMode::PreferSerialized;
+    else if (*forceModuleLoadingMode == "only-interface" ||
+             *forceModuleLoadingMode == "only-parseable")
+      Opts.ModuleLoadMode = ModuleLoadingMode::OnlyInterface;
+    else if (*forceModuleLoadingMode == "only-serialized")
+      Opts.ModuleLoadMode = ModuleLoadingMode::OnlySerialized;
+    else
+      Diags.diagnose(SourceLoc(), diag::unknown_forced_module_loading_mode,
+                     *forceModuleLoadingMode);
+  }
+
   // Opts.RuntimeIncludePath is set by calls to
   // setRuntimeIncludePath() or setMainExecutablePath().
   // Opts.RuntimeImportPath is set by calls to
diff --git a/lib/Frontend/Frontend.cpp b/lib/Frontend/Frontend.cpp
index 099b4e161f98d..94d76433bd9f6 100644
--- a/lib/Frontend/Frontend.cpp
+++ b/lib/Frontend/Frontend.cpp
@@ -709,26 +709,7 @@ bool CompilerInstance::setUpModuleLoaders() {
                                                   enableLibraryEvolution,
                                                   getDependencyTracker()));
   }
-  auto MLM = ModuleLoadingMode::PreferSerialized;
-  if (auto forceModuleLoadingMode =
-      llvm::sys::Process::GetEnv("SWIFT_FORCE_MODULE_LOADING")) {
-    if (*forceModuleLoadingMode == "prefer-interface" ||
-        *forceModuleLoadingMode == "prefer-parseable")
-      MLM = ModuleLoadingMode::PreferInterface;
-    else if (*forceModuleLoadingMode == "prefer-serialized")
-      MLM = ModuleLoadingMode::PreferSerialized;
-    else if (*forceModuleLoadingMode == "only-interface" ||
-             *forceModuleLoadingMode == "only-parseable")
-      MLM = ModuleLoadingMode::OnlyInterface;
-    else if (*forceModuleLoadingMode == "only-serialized")
-      MLM = ModuleLoadingMode::OnlySerialized;
-    else {
-      Diagnostics.diagnose(SourceLoc(),
-                           diag::unknown_forced_module_loading_mode,
-                           *forceModuleLoadingMode);
-      return true;
-    }
-  }
+  auto MLM = Invocation.getSearchPathOptions().ModuleLoadMode;
   auto IgnoreSourceInfoFile =
     Invocation.getFrontendOptions().IgnoreSwiftSourceInfo;
   if (Invocation.getLangOptions().EnableMemoryBufferImporter) {
diff --git a/lib/Frontend/ModuleInterfaceLoader.cpp b/lib/Frontend/ModuleInterfaceLoader.cpp
index 04e93b05f1a13..d065f3837d1f6 100644
--- a/lib/Frontend/ModuleInterfaceLoader.cpp
+++ b/lib/Frontend/ModuleInterfaceLoader.cpp
@@ -1372,7 +1372,8 @@ std::error_code ModuleInterfaceLoader::findModuleFilesInDirectory(
 }
 
 std::vector<std::string>
-ModuleInterfaceCheckerImpl::getCompiledModuleCandidatesForInterface(StringRef moduleName, StringRef interfacePath) {
+ModuleInterfaceCheckerImpl::getCompiledModuleCandidatesForInterface(
+    StringRef moduleName, StringRef interfacePath) {
   // Derive .swiftmodule path from the .swiftinterface path.
   auto interfaceExt = file_types::getExtension(file_types::TY_SwiftModuleInterfaceFile);
   auto newExt = file_types::getExtension(file_types::TY_SwiftModuleFile);
@@ -1392,17 +1393,32 @@ ModuleInterfaceCheckerImpl::getCompiledModuleCandidatesForInterface(StringRef mo
 
   ModuleInterfaceLoaderImpl Impl(Ctx, modulePath, interfacePath, moduleName,
                                  CacheDir, PrebuiltCacheDir, BackupInterfaceDir,
-                                 SourceLoc(), Opts,
-                                 RequiresOSSAModules,
-                                 nullptr,
-                                 ModuleLoadingMode::PreferSerialized);
+                                 SourceLoc(), Opts, RequiresOSSAModules,
+                                 nullptr, Ctx.SearchPathOpts.ModuleLoadMode);
   std::vector<std::string> results;
-  auto pair = Impl.getCompiledModuleCandidates();
-  // Add compiled module candidates only when they are non-empty.
-  if (!pair.first.empty())
-    results.push_back(pair.first);
-  if (!pair.second.empty())
-    results.push_back(pair.second);
+  std::string adjacentMod, prebuiltMod;
+  std::tie(adjacentMod, prebuiltMod) = Impl.getCompiledModuleCandidates();
+
+  auto validateModule = [&](StringRef modulePath) {
+    // Legacy behavior do not validate module.
+    if (Ctx.SearchPathOpts.NoScannerModuleValidation)
+      return true;
+
+    // If we picked the other module already, no need to validate this one since
+    // it should not be used anyway.
+    if (!results.empty())
+      return false;
+    SmallVector<FileDependency, 16> deps;
+    std::unique_ptr<llvm::MemoryBuffer> moduleBuffer;
+    return Impl.upToDateChecker.swiftModuleIsUpToDate(
+        modulePath, Impl.rebuildInfo, deps, moduleBuffer);
+  };
+
+  // Add compiled module candidates only when they are non-empty and up-to-date.
+  if (!adjacentMod.empty() && validateModule(adjacentMod))
+    results.push_back(adjacentMod);
+  if (!prebuiltMod.empty() && validateModule(prebuiltMod))
+    results.push_back(prebuiltMod);
   return results;
 }
 
@@ -1862,6 +1878,12 @@ InterfaceSubContextDelegateImpl::InterfaceSubContextDelegateImpl(
   genericSubInvocation.getSearchPathOptions().PluginSearchOpts =
       searchPathOpts.PluginSearchOpts;
 
+  // Get module loading behavior options.
+  genericSubInvocation.getSearchPathOptions().NoScannerModuleValidation =
+      searchPathOpts.NoScannerModuleValidation;
+  genericSubInvocation.getSearchPathOptions().ModuleLoadMode =
+      searchPathOpts.ModuleLoadMode;
+
   auto &subClangImporterOpts = genericSubInvocation.getClangImporterOptions();
   // Respect the detailed-record preprocessor setting of the parent context.
   // This, and the "raw" clang module format it implicitly enables, are
diff --git a/lib/Sema/TypeCheckMacros.cpp b/lib/Sema/TypeCheckMacros.cpp
index 84a0d273f150f..efdcc35414c02 100644
--- a/lib/Sema/TypeCheckMacros.cpp
+++ b/lib/Sema/TypeCheckMacros.cpp
@@ -290,7 +290,9 @@ initializeExecutablePlugin(ASTContext &ctx,
   if (!libraryPath.empty()) {
 #if SWIFT_BUILD_SWIFT_SYNTAX
     llvm::SmallString<128> resolvedLibraryPath;
-    auto fs = ctx.SourceMgr.getFileSystem();
+    auto fs = ctx.ClangImporterOpts.HasClangIncludeTreeRoot
+                  ? llvm::vfs::getRealFileSystem()
+                  : ctx.SourceMgr.getFileSystem();
     if (auto err = fs->getRealPath(libraryPath, resolvedLibraryPath)) {
       return llvm::createStringError(err, err.message());
     }
diff --git a/lib/Serialization/ScanningLoaders.cpp b/lib/Serialization/ScanningLoaders.cpp
index a9dd8a9daba67..0bb53171a8c37 100644
--- a/lib/Serialization/ScanningLoaders.cpp
+++ b/lib/Serialization/ScanningLoaders.cpp
@@ -33,6 +33,7 @@
 #include "llvm/Support/Threading.h"
 #include "llvm/Support/VirtualFileSystem.h"
 #include <algorithm>
+#include <system_error>
 
 using namespace swift;
 
@@ -55,7 +56,8 @@ std::error_code SwiftModuleScanner::findModuleFilesInDirectory(
   if (LoadMode == ModuleLoadingMode::OnlySerialized || !InPath) {
     if (fs.exists(ModPath)) {
       // The module file will be loaded directly.
-      auto dependencies = scanModuleFile(ModPath, IsFramework);
+      auto dependencies =
+          scanModuleFile(ModPath, IsFramework, isTestableDependencyLookup);
       if (dependencies) {
         this->dependencies = std::move(dependencies.get());
         return std::error_code();
@@ -66,7 +68,8 @@ std::error_code SwiftModuleScanner::findModuleFilesInDirectory(
   }
   assert(InPath);
 
-  auto dependencies = scanInterfaceFile(*InPath, IsFramework);
+  auto dependencies =
+      scanInterfaceFile(*InPath, IsFramework, isTestableDependencyLookup);
   if (dependencies) {
     this->dependencies = std::move(dependencies.get());
     return std::error_code();
@@ -133,7 +136,7 @@ static std::vector<std::string> getCompiledCandidates(ASTContext &ctx,
 
 llvm::ErrorOr<ModuleDependencyInfo>
 SwiftModuleScanner::scanInterfaceFile(Twine moduleInterfacePath,
-                                      bool isFramework) {
+                                      bool isFramework, bool isTestableImport) {
   // Create a module filename.
   // FIXME: Query the module interface loader to determine an appropriate
   // name for the module, which includes an appropriate hash.
@@ -152,8 +155,23 @@ SwiftModuleScanner::scanInterfaceFile(Twine moduleInterfacePath,
         std::string InPath = moduleInterfacePath.str();
         auto compiledCandidates =
             getCompiledCandidates(Ctx, realModuleName.str(), InPath);
-        std::vector<std::string> Args(BaseArgs.begin(), BaseArgs.end());
+        if (!compiledCandidates.empty() &&
+            !Ctx.SearchPathOpts.NoScannerModuleValidation) {
+          assert(compiledCandidates.size() == 1 &&
+                 "Should only have 1 candidate module");
+          auto BinaryDep = scanModuleFile(compiledCandidates[0], isFramework,
+                                          isTestableImport);
+          if (BinaryDep) {
+            Result = *BinaryDep;
+            return std::error_code();
+          }
 
+          // If return no such file, just fallback to use interface.
+          if (BinaryDep.getError() != std::errc::no_such_file_or_directory)
+            return BinaryDep.getError();
+        }
+
+        std::vector<std::string> Args(BaseArgs.begin(), BaseArgs.end());
         // Add explicit Swift dependency compilation flags
         Args.push_back("-explicit-interface-module-build");
         Args.push_back("-disable-implicit-swift-modules");
diff --git a/lib/Serialization/Serialization.cpp b/lib/Serialization/Serialization.cpp
index ce21cc0863e84..3e44ab7148a7d 100644
--- a/lib/Serialization/Serialization.cpp
+++ b/lib/Serialization/Serialization.cpp
@@ -1320,21 +1320,25 @@ void Serializer::writeInputBlock() {
     time_t importedHeaderModTime = 0;
     std::string contents;
     auto importedHeaderPath = Options.ImportedHeader;
+    std::string pchIncludeTree;
     // We do not want to serialize the explicitly-specified .pch path if one was
     // provided. Instead we write out the path to the original header source so
     // that clients can consume it.
     if (Options.ExplicitModuleBuild &&
         llvm::sys::path::extension(importedHeaderPath)
-            .endswith(file_types::getExtension(file_types::TY_PCH)))
-      importedHeaderPath = clangImporter->getClangInstance()
-                               .getASTReader()
-                               ->getModuleManager()
-                               .lookupByFileName(importedHeaderPath)
-                               ->OriginalSourceFileName;
+            .ends_with(file_types::getExtension(file_types::TY_PCH))) {
+      auto *pch = clangImporter->getClangInstance()
+                      .getASTReader()
+                      ->getModuleManager()
+                      .lookupByFileName(importedHeaderPath);
+      pchIncludeTree = pch->IncludeTreeID;
+      importedHeaderPath = pch->OriginalSourceFileName;
+    }
 
     if (!importedHeaderPath.empty()) {
       contents = clangImporter->getBridgingHeaderContents(
-          importedHeaderPath, importedHeaderSize, importedHeaderModTime);
+          importedHeaderPath, importedHeaderSize, importedHeaderModTime,
+          pchIncludeTree);
     }
     assert(publicImportSet.count(bridgingHeaderImport));
     ImportedHeader.emit(ScratchRecord,
diff --git a/lib/Serialization/SerializedModuleLoader.cpp b/lib/Serialization/SerializedModuleLoader.cpp
index 3fca53c35caa7..6f888e8243cb9 100644
--- a/lib/Serialization/SerializedModuleLoader.cpp
+++ b/lib/Serialization/SerializedModuleLoader.cpp
@@ -25,6 +25,7 @@
 #include "swift/Basic/Version.h"
 #include "swift/Frontend/ModuleInterfaceLoader.h"
 #include "swift/Option/Options.h"
+#include "swift/Serialization/Validation.h"
 
 #include "llvm/Option/OptTable.h"
 #include "llvm/Option/ArgList.h"
@@ -391,26 +392,14 @@ std::error_code SerializedModuleLoaderBase::openModuleFile(
   return std::error_code();
 }
 
-llvm::ErrorOr<SerializedModuleLoaderBase::BinaryModuleImports>
+SerializedModuleLoaderBase::BinaryModuleImports
 SerializedModuleLoaderBase::getImportsOfModule(
-    Twine modulePath, ModuleLoadingBehavior transitiveBehavior,
-    bool isFramework, bool isRequiredOSSAModules, StringRef SDKName,
-    StringRef packageName, llvm::vfs::FileSystem *fileSystem,
-    PathObfuscator &recoverer) {
-  auto moduleBuf = fileSystem->getBufferForFile(modulePath);
-  if (!moduleBuf)
-    return moduleBuf.getError();
-
+    const ModuleFileSharedCore &loadedModuleFile,
+    ModuleLoadingBehavior transitiveBehavior, StringRef packageName,
+    bool isTestableImport) {
   llvm::StringSet<> importedModuleNames;
   std::string importedHeader = "";
-  // Load the module file without validation.
-  std::shared_ptr<const ModuleFileSharedCore> loadedModuleFile;
-  serialization::ValidationInfo loadInfo = ModuleFileSharedCore::load(
-      "", "", std::move(moduleBuf.get()), nullptr, nullptr, isFramework,
-      isRequiredOSSAModules,
-      SDKName, recoverer, loadedModuleFile);
-
-  for (const auto &dependency : loadedModuleFile->getDependencies()) {
+  for (const auto &dependency : loadedModuleFile.getDependencies()) {
     if (dependency.isHeader()) {
       assert(importedHeader.empty() &&
              "Unexpected more than one header dependency");
@@ -419,11 +408,10 @@ SerializedModuleLoaderBase::getImportsOfModule(
     }
 
     ModuleLoadingBehavior dependencyTransitiveBehavior =
-        loadedModuleFile->getTransitiveLoadingBehavior(
+        loadedModuleFile.getTransitiveLoadingBehavior(
             dependency,
             /*debuggerMode*/ false,
-            /*isPartialModule*/ false, packageName,
-            loadedModuleFile->isTestable());
+            /*isPartialModule*/ false, packageName, isTestableImport);
     if (dependencyTransitiveBehavior > transitiveBehavior)
       continue;
 
@@ -437,41 +425,53 @@ SerializedModuleLoaderBase::getImportsOfModule(
     importedModuleNames.insert(moduleName);
   }
 
-  return SerializedModuleLoaderBase::BinaryModuleImports{importedModuleNames, importedHeader};
+  return SerializedModuleLoaderBase::BinaryModuleImports{importedModuleNames,
+                                                         importedHeader};
 }
 
 llvm::ErrorOr<ModuleDependencyInfo>
-SerializedModuleLoaderBase::scanModuleFile(Twine modulePath, bool isFramework) {
+SerializedModuleLoaderBase::scanModuleFile(Twine modulePath, bool isFramework,
+                                           bool isTestableImport) {
   const std::string moduleDocPath;
   const std::string sourceInfoPath;
+
+  // Read and valid module.
+  auto moduleBuf = Ctx.SourceMgr.getFileSystem()->getBufferForFile(modulePath);
+  if (!moduleBuf)
+    return moduleBuf.getError();
+
+  std::shared_ptr<const ModuleFileSharedCore> loadedModuleFile;
+  serialization::ValidationInfo loadInfo = ModuleFileSharedCore::load(
+      "", "", std::move(moduleBuf.get()), nullptr, nullptr, isFramework,
+      isRequiredOSSAModules(), Ctx.LangOpts.SDKName,
+      Ctx.SearchPathOpts.DeserializedPathRecoverer, loadedModuleFile);
+
+  if (!Ctx.SearchPathOpts.NoScannerModuleValidation) {
+    // If failed to load, just ignore and return do not found.
+    if (loadInfo.status != serialization::Status::Valid) {
+      if (Ctx.LangOpts.EnableModuleLoadingRemarks)
+        Ctx.Diags.diagnose(SourceLoc(), diag::skip_module_invalid,
+                           modulePath.str());
+      return std::make_error_code(std::errc::no_such_file_or_directory);
+    }
+  }
+
   // Some transitive dependencies of binary modules are not required to be
   // imported during normal builds.
   // TODO: This is worth revisiting for debugger purposes where
   //       loading the module is optional, and implementation-only imports
   //       from modules with testing enabled where the dependency is
   //       optional.
-  ModuleLoadingBehavior transitiveLoadingBehavior =
-      ModuleLoadingBehavior::Required;
-  auto binaryModuleImports = getImportsOfModule(
-      modulePath, transitiveLoadingBehavior, isFramework,
-      isRequiredOSSAModules(),
-      Ctx.LangOpts.SDKName, Ctx.LangOpts.PackageName,
-      Ctx.SourceMgr.getFileSystem().get(),
-      Ctx.SearchPathOpts.DeserializedPathRecoverer);
-  if (!binaryModuleImports)
-    return binaryModuleImports.getError();
+  auto binaryModuleImports =
+      getImportsOfModule(*loadedModuleFile, ModuleLoadingBehavior::Required,
+                         Ctx.LangOpts.PackageName, isTestableImport);
 
   // Lookup optional imports of this module also
-  auto binaryModuleOptionalImports = getImportsOfModule(
-      modulePath, ModuleLoadingBehavior::Optional, isFramework,
-      isRequiredOSSAModules(),
-      Ctx.LangOpts.SDKName, Ctx.LangOpts.PackageName,
-      Ctx.SourceMgr.getFileSystem().get(),
-      Ctx.SearchPathOpts.DeserializedPathRecoverer);
-  if (!binaryModuleOptionalImports)
-    return binaryModuleImports.getError();
+  auto binaryModuleOptionalImports =
+      getImportsOfModule(*loadedModuleFile, ModuleLoadingBehavior::Optional,
+                         Ctx.LangOpts.PackageName, isTestableImport);
 
-  auto importedModuleSet = binaryModuleImports.get().moduleImports;
+  auto importedModuleSet = binaryModuleImports.moduleImports;
   std::vector<std::string> importedModuleNames;
   importedModuleNames.reserve(importedModuleSet.size());
   llvm::transform(importedModuleSet.keys(),
@@ -480,8 +480,8 @@ SerializedModuleLoaderBase::scanModuleFile(Twine modulePath, bool isFramework) {
                      return N.str();
                   });
 
-  auto importedHeader = binaryModuleImports.get().headerImport;
-  auto &importedOptionalModuleSet = binaryModuleOptionalImports.get().moduleImports;
+  auto importedHeader = binaryModuleImports.headerImport;
+  auto &importedOptionalModuleSet = binaryModuleOptionalImports.moduleImports;
   std::vector<std::string> importedOptionalModuleNames;
   for (const auto optionalImportedModule : importedOptionalModuleSet.keys())
     if (!importedModuleSet.contains(optionalImportedModule))
@@ -790,7 +790,8 @@ bool SerializedModuleLoaderBase::findModule(
       auto result = findModuleFilesInDirectory(
           moduleID, absoluteBaseName, moduleInterfacePath,
           moduleInterfaceSourcePath, moduleBuffer, moduleDocBuffer,
-          moduleSourceInfoBuffer, skipBuildingInterface, isFramework);
+          moduleSourceInfoBuffer, skipBuildingInterface, isFramework,
+          isTestableDependencyLookup);
       if (!result)
         return true;
       if (result == std::errc::not_supported)
diff --git a/test/CAS/Xcc_args.swift b/test/CAS/Xcc_args.swift
index 0ffbe0ace877d..498635f0a7fc5 100644
--- a/test/CAS/Xcc_args.swift
+++ b/test/CAS/Xcc_args.swift
@@ -5,14 +5,11 @@
 // RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import \
 // RUN:   %t/test.swift -o %t/deps.json -swift-version 5 -cache-compile-job -cas-path %t/cas -Xcc -D_VERSION=1 \
 // RUN:   -Xcc -fmodule-map-file=%t/include/module.modulemap -Xcc -ivfsoverlay -Xcc %t/empty.yaml \
-// RUN:   -Xcc -I%t/empty.hmap
+// RUN:   -Xcc -I%t/empty.hmap -module-load-mode prefer-serialized
 
 // RUN: %{python} %S/Inputs/BuildCommandExtractor.py %t/deps.json clang:SwiftShims > %t/shims.cmd
 // RUN: %swift_frontend_plain @%t/shims.cmd
 
-// RUN: %{python} %S/Inputs/BuildCommandExtractor.py %t/deps.json Swift > %t/swift.cmd
-// RUN: %swift_frontend_plain @%t/swift.cmd
-
 // RUN: %{python} %S/Inputs/BuildCommandExtractor.py %t/deps.json clang:_Macro > %t/Macro.cmd
 // RUN: %swift_frontend_plain @%t/Macro.cmd
 
diff --git a/test/CAS/bridging-header.swift b/test/CAS/bridging-header.swift
index cae66faa194ae..bc0691e9af0f9 100644
--- a/test/CAS/bridging-header.swift
+++ b/test/CAS/bridging-header.swift
@@ -1,6 +1,12 @@
+// REQUIRES: objc_interop
 // RUN: %empty-directory(%t)
 // RUN: split-file %s %t
 
+// RUN: %target-swift-frontend -emit-module -o %t/temp.swiftmodule -module-name Test -swift-version 5 \
+// RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import \
+// RUN:   -Xcc -fmodule-map-file=%t/a.modulemap -Xcc -fmodule-map-file=%t/b.modulemap -import-objc-header %t/Bridging.h \
+// RUN:   %t/test.swift
+
 // RUN: %target-swift-frontend -scan-dependencies -module-name Test -module-cache-path %t/clang-module-cache -O \
 // RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import \
 // RUN:   %t/test.swift -o %t/deps.json -swift-version 5 -cache-compile-job -cas-path %t/cas \
@@ -27,21 +33,103 @@
 // CHECK-NEXT:    "-Xcc",
 // CHECK-NEXT:    "llvmcas://{{.*}}"
 
+/// Try build then import from a non-caching compilation.
+
+// RUN: %{python} %S/Inputs/BuildCommandExtractor.py %t/deps.json clang:SwiftShims > %t/shim.cmd
+// RUN: %swift_frontend_plain @%t/shim.cmd
+// RUN: %{python} %S/Inputs/BuildCommandExtractor.py %t/deps.json clang:B > %t/B.cmd
+// RUN: %swift_frontend_plain @%t/B.cmd
+// RUN: %{python} %S/Inputs/BuildCommandExtractor.py %t/deps.json clang:A > %t/A.cmd
+// RUN: %swift_frontend_plain @%t/A.cmd
+
+// RUN: %{python} %S/Inputs/GenerateExplicitModuleMap.py %t/deps.json > %t/map.json
+// RUN: llvm-cas --cas %t/cas --make-blob --data %t/map.json > %t/map.casid
+
+// RUN: %{python} %S/Inputs/BuildCommandExtractor.py %t/deps.json bridgingHeader | tail -n +2  > %t/header.cmd
+// RUN: %target-swift-frontend @%t/header.cmd -disable-implicit-swift-modules %t/Bridging.h -O -o %t/bridging.pch
+// RUN: %cache-tool -cas-path %t/cas -cache-tool-action print-output-keys -- \
+// RUN:   %target-swift-frontend @%t/header.cmd -disable-implicit-swift-modules %t/Bridging.h -O -o %t/bridging.pch > %t/keys.json
+// RUN: %{python} %S/Inputs/ExtractOutputKey.py %t/keys.json %t/Bridging.h > %t/key
+
+// RUN: %{python} %S/Inputs/BuildCommandExtractor.py %t/deps.json Test > %t/MyApp.cmd
+// RUN: echo "\"-disable-implicit-string-processing-module-import\"" >> %t/MyApp.cmd
+// RUN: echo "\"-disable-implicit-concurrency-module-import\"" >> %t/MyApp.cmd
+// RUN: echo "\"-disable-implicit-swift-modules\"" >> %t/MyApp.cmd
+// RUN: echo "\"-import-objc-header\"" >> %t/MyApp.cmd
+// RUN: echo "\"%t/bridging.pch\"" >> %t/MyApp.cmd
+// RUN: echo "\"-bridging-header-pch-key\"" >> %t/MyApp.cmd
+// RUN: echo "\"@%t/key\"" >> %t/MyApp.cmd
+// RUN: echo "\"-explicit-swift-module-map-file\"" >> %t/MyApp.cmd
+// RUN: echo "\"@%t/map.casid\"" >> %t/MyApp.cmd
+
+// RUN: %target-swift-frontend  -cache-compile-job -module-name Test -O -cas-path %t/cas @%t/MyApp.cmd %t/test.swift \
+// RUN:   -emit-module -o %t/Test.swiftmodule
+
+/// Importing binary module with bridging header built from CAS from a regluar build.
+/// This should succeed even it is also importing a bridging header that shares same header dependencies (with proper header guard).
+// RUN: %target-swift-frontend -typecheck -module-name User -swift-version 5 \
+// RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import \
+// RUN:   -Xcc -fmodule-map-file=%t/a.modulemap -Xcc -fmodule-map-file=%t/b.modulemap \
+// RUN:   -I %t %t/user.swift -import-objc-header %t/Bridging2.h
+
+/// Importing binary module with bridging header built from CAS from a cached build. This should work without additional bridging header deps.
+// RUN: %target-swift-frontend -scan-dependencies -module-name User -module-cache-path %t/clang-module-cache -O \
+// RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import \
+// RUN:   %t/user.swift -o %t/deps2.json -swift-version 5 -cache-compile-job -cas-path %t/cas \
+// RUN:   -Xcc -fmodule-map-file=%t/a.modulemap -Xcc -fmodule-map-file=%t/b.modulemap -I %t
+
+// RUN: %{python} %S/Inputs/GenerateExplicitModuleMap.py %t/deps2.json > %t/map2.json
+// RUN: llvm-cas --cas %t/cas --make-blob --data %t/map2.json > %t/map2.casid
+// RUN: %{python} %S/Inputs/BuildCommandExtractor.py %t/deps2.json User > %t/User.cmd
+// RUN: %target-swift-frontend  -cache-compile-job -module-name User -O -cas-path %t/cas \
+// RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import -disable-implicit-swift-modules \
+// RUN:   -explicit-swift-module-map-file @%t/map2.casid @%t/User.cmd %t/user.swift \
+// RUN:   -emit-module -o %t/User.swiftmodule
+
 //--- test.swift
-import B
-public func test() {}
+public func test() {
+    b()
+}
+public class TestB: B {}
+
+//--- user.swift
+import Test
+
+func user() {
+  var b: TestB
+  test()
+}
+
+extension A {
+    public func testA() {}
+}
+
 
 //--- Bridging.h
 #include "Foo.h"
+#include "Foo2.h"
+
+//--- Bridging2.h
+#include "Foo.h"
+#include "Foo2.h"
 
 //--- Foo.h
 #import "a.h"
 
+//--- Foo2.h
+#pragma once
+int Foo = 0;
+
 //--- a.h
 #include "b.h"
+struct A {
+  int a;
+};
 
 //--- b.h
 void b(void);
+@interface B
+@end
 
 //--- a.modulemap
 module A {
diff --git a/test/CAS/cached_diagnostics.swift b/test/CAS/cached_diagnostics.swift
index 3bb71963b33b7..8ac6bd000da2e 100644
--- a/test/CAS/cached_diagnostics.swift
+++ b/test/CAS/cached_diagnostics.swift
@@ -5,12 +5,10 @@
 
 // RUN: %target-swift-frontend -scan-dependencies -module-name Test -O -import-objc-header %S/Inputs/objc.h \
 // RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import \
-// RUN:   %s -o %t/deps.json -cache-compile-job -cas-path %t/cas
+// RUN:   %s -o %t/deps.json -cache-compile-job -cas-path %t/cas -module-load-mode prefer-serialized
 
 // RUN: %{python} %S/Inputs/BuildCommandExtractor.py %t/deps.json clang:SwiftShims > %t/shim.cmd
 // RUN: %swift_frontend_plain @%t/shim.cmd
-// RUN: %{python} %S/Inputs/BuildCommandExtractor.py %t/deps.json Swift > %t/swift.cmd
-// RUN: %swift_frontend_plain @%t/swift.cmd
 
 // RUN: %{python} %S/Inputs/BuildCommandExtractor.py %t/deps.json bridgingHeader | tail -n +2  > %t/header.cmd
 // RUN: %target-swift-frontend @%t/header.cmd -disable-implicit-swift-modules %S/Inputs/objc.h -O -o %t/objc.pch 2>&1 | %FileCheck %s -check-prefix CHECK-BRIDGE
diff --git a/test/CAS/cross_import.swift b/test/CAS/cross_import.swift
index 9e34140953536..9abba2673f00a 100644
--- a/test/CAS/cross_import.swift
+++ b/test/CAS/cross_import.swift
@@ -15,7 +15,7 @@
 
 // RUN: %target-swift-frontend -scan-dependencies -module-name Test -module-cache-path %t/clang-module-cache %t/main.swift \
 // RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import -parse-stdlib \
-// RUN:   -o %t/deps.json -I %t -cache-compile-job -cas-path %t/cas -swift-version 5 -enable-cross-import-overlays
+// RUN:   -o %t/deps.json -I %t -cache-compile-job -cas-path %t/cas -swift-version 5 -enable-cross-import-overlays -module-load-mode prefer-interface
 
 // RUN: %{python} %S/Inputs/BuildCommandExtractor.py %t/deps.json A > %t/A.cmd
 // RUN: %swift_frontend_plain @%t/A.cmd
diff --git a/test/CAS/index-store.swift b/test/CAS/index-store.swift
index 5e39880edef21..421fa3e105ad7 100644
--- a/test/CAS/index-store.swift
+++ b/test/CAS/index-store.swift
@@ -7,7 +7,7 @@
 // RUN:   -emit-module-interface-path %t/A.swiftinterface \
 // RUN:   -o %t/A.swiftmodule
 
-// RUN: %target-swift-frontend -scan-dependencies -module-name Test -O -module-cache-path %t/clang-module-cache \
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -module-name Test -O -module-cache-path %t/clang-module-cache \
 // RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import -parse-stdlib \
 // RUN:   %t/test.swift -I %t -o %t/deps.json -cache-compile-job -cas-path %t/cas
 
diff --git a/test/CAS/macro_option_set.swift b/test/CAS/macro_option_set.swift
new file mode 100644
index 0000000000000..f2e95a4dd749b
--- /dev/null
+++ b/test/CAS/macro_option_set.swift
@@ -0,0 +1,53 @@
+// REQUIRES: swift_swift_parser
+
+// RUN: %empty-directory(%t)
+
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-serialized -module-name MyApp -module-cache-path %t/clang-module-cache -O \
+// RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import \
+// RUN:   %s -o %t/deps.json -swift-version 5 -cache-compile-job -cas-path %t/cas -plugin-path %swift-plugin-dir
+
+// RUN: %S/Inputs/SwiftDepsExtractor.py %t/deps.json MyApp casFSRootID > %t/fs.casid
+// RUN: llvm-cas -cas %t/cas -ls-tree-recursive @%t/fs.casid | %FileCheck %s --check-prefix=FS
+
+// FS: SwiftMacros
+
+// RUN: %S/Inputs/BuildCommandExtractor.py %t/deps.json clang:SwiftShims > %t/SwiftShims.cmd
+// RUN: %swift_frontend_plain @%t/SwiftShims.cmd
+
+// RUN: %S/Inputs/BuildCommandExtractor.py %t/deps.json MyApp > %t/MyApp.cmd
+// RUN: %{python} %S/Inputs/GenerateExplicitModuleMap.py %t/deps.json > %t/map.json
+// RUN: llvm-cas --cas %t/cas --make-blob --data %t/map.json > %t/map.casid
+
+// RUN: %target-swift-frontend \
+// RUN:   -typecheck -verify -cache-compile-job -cas-path %t/cas \
+// RUN:   -swift-version 5 -disable-implicit-swift-modules \
+// RUN:   -plugin-path %swift-plugin-dir \
+// RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import \
+// RUN:   -module-name MyApp -explicit-swift-module-map-file @%t/map.casid \
+// RUN:   %s @%t/MyApp.cmd
+
+import Swift
+
+@attached(member, names: named(RawValue), named(rawValue), named(`init`), arbitrary)
+@attached(extension, conformances: OptionSet)
+public macro OptionSet<RawType>() =
+  #externalMacro(module: "SwiftMacros", type: "OptionSetMacro")
+
+@OptionSet<UInt8>
+struct ShippingOptions {
+  private enum Options: Int {
+    case nextDay
+    case secondDay
+    case priority
+    case standard
+  }
+
+  static let express: ShippingOptions = [.nextDay, .secondDay]
+  static let all: ShippingOptions = [.express, .priority, .standard]
+}
+
+let options = ShippingOptions.express
+assert(options.contains(.nextDay))
+assert(options.contains(.secondDay))
+assert(!options.contains(.standard))
+
diff --git a/test/CAS/macro_plugin.swift b/test/CAS/macro_plugin.swift
new file mode 100644
index 0000000000000..71c26e32b675e
--- /dev/null
+++ b/test/CAS/macro_plugin.swift
@@ -0,0 +1,73 @@
+// REQUIRES: swift_swift_parser
+
+/// Test loading and external library through `-load-plugin-library`
+/// TODO: switch this test case to use `-external-plugin-path`.
+
+// RUN: %empty-directory(%t)
+// RUN: %empty-directory(%t/plugins)
+//
+//== Build the plugin library
+// RUN: %host-build-swift \
+// RUN:   -swift-version 5 \
+// RUN:   -emit-library \
+// RUN:   -o %t/plugins/%target-library-name(MacroDefinition) \
+// RUN:   -module-name=MacroDefinition \
+// RUN:   %S/../Macros/Inputs/syntax_macro_definitions.swift \
+// RUN:   -g -no-toolchain-stdlib-rpath
+
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-serialized -module-name MyApp -module-cache-path %t/clang-module-cache -O \
+// RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import \
+// RUN:   %s -o %t/deps.json -swift-version 5 -cache-compile-job -cas-path %t/cas -load-plugin-library %t/plugins/%target-library-name(MacroDefinition)
+
+// RUN: %S/Inputs/SwiftDepsExtractor.py %t/deps.json MyApp casFSRootID > %t/fs.casid
+// RUN: llvm-cas -cas %t/cas -ls-tree-recursive @%t/fs.casid | %FileCheck %s --check-prefix=FS
+
+// FS: MacroDefinition
+
+// RUN: %S/Inputs/BuildCommandExtractor.py %t/deps.json clang:SwiftShims > %t/SwiftShims.cmd
+// RUN: %swift_frontend_plain @%t/SwiftShims.cmd
+
+// RUN: %S/Inputs/BuildCommandExtractor.py %t/deps.json MyApp > %t/MyApp.cmd
+// RUN: %{python} %S/Inputs/GenerateExplicitModuleMap.py %t/deps.json > %t/map.json
+// RUN: llvm-cas --cas %t/cas --make-blob --data %t/map.json > %t/map.casid
+
+// RUN: %target-swift-frontend \
+// RUN:   -typecheck -verify -cache-compile-job -cas-path %t/cas \
+// RUN:   -swift-version 5 -disable-implicit-swift-modules \
+// RUN:   -load-plugin-library %t/plugins/%target-library-name(MacroDefinition) \
+// RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import \
+// RUN:   -module-name MyApp -explicit-swift-module-map-file @%t/map.casid \
+// RUN:   %s @%t/MyApp.cmd
+
+@attached(extension, conformances: P, names: named(requirement))
+macro DelegatedConformance() = #externalMacro(module: "MacroDefinition", type: "DelegatedConformanceViaExtensionMacro")
+
+protocol P {
+  static func requirement()
+}
+
+struct Wrapped: P {
+  static func requirement() {
+    print("Wrapped.requirement")
+  }
+}
+
+@DelegatedConformance
+struct Generic<Element> {}
+
+// CHECK: {"expandMacroResult":{"diagnostics":[],"expandedSource":"extension Generic: P where Element: P {\n  static func requirement() {\n    Element.requirement()\n  }\n}"}}
+
+func requiresP(_ value: (some P).Type) {
+  value.requirement()
+}
+
+requiresP(Generic<Wrapped>.self)
+
+struct Outer {
+  @DelegatedConformance
+  struct Nested<Element> {}
+}
+
+// CHECK: {"expandMacroResult":{"diagnostics":[],"expandedSource":"extension Outer.Nested: P where Element: P {\n  static func requirement() {\n    Element.requirement()\n  }\n}"}}
+
+requiresP(Outer.Nested<Wrapped>.self)
diff --git a/test/CAS/macro_plugin_external.swift b/test/CAS/macro_plugin_external.swift
new file mode 100644
index 0000000000000..7a904f4d3172a
--- /dev/null
+++ b/test/CAS/macro_plugin_external.swift
@@ -0,0 +1,73 @@
+// REQUIRES: swift_swift_parser
+
+/// Test loading and external library through `-load-plugin-library`
+/// TODO: switch this test case to use `-external-plugin-path`.
+
+// RUN: %empty-directory(%t)
+// RUN: %empty-directory(%t/plugins)
+//
+//== Build the plugin library
+// RUN: %host-build-swift \
+// RUN:   -swift-version 5 \
+// RUN:   -emit-library \
+// RUN:   -o %t/plugins/%target-library-name(MacroDefinition) \
+// RUN:   -module-name=MacroDefinition \
+// RUN:   %S/../Macros/Inputs/syntax_macro_definitions.swift \
+// RUN:   -g -no-toolchain-stdlib-rpath
+
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-serialized -module-name MyApp -module-cache-path %t/clang-module-cache -O \
+// RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import \
+// RUN:   %s -o %t/deps.json -swift-version 5 -cache-compile-job -cas-path %t/cas -external-plugin-path %t/plugins#%swift-plugin-server
+
+// RUN: %S/Inputs/SwiftDepsExtractor.py %t/deps.json MyApp casFSRootID > %t/fs.casid
+// RUN: llvm-cas -cas %t/cas -ls-tree-recursive @%t/fs.casid | %FileCheck %s --check-prefix=FS
+
+// FS: MacroDefinition
+
+// RUN: %S/Inputs/BuildCommandExtractor.py %t/deps.json clang:SwiftShims > %t/SwiftShims.cmd
+// RUN: %swift_frontend_plain @%t/SwiftShims.cmd
+
+// RUN: %S/Inputs/BuildCommandExtractor.py %t/deps.json MyApp > %t/MyApp.cmd
+// RUN: %{python} %S/Inputs/GenerateExplicitModuleMap.py %t/deps.json > %t/map.json
+// RUN: llvm-cas --cas %t/cas --make-blob --data %t/map.json > %t/map.casid
+
+// RUN: %target-swift-frontend \
+// RUN:   -typecheck -verify -cache-compile-job -cas-path %t/cas \
+// RUN:   -swift-version 5 -disable-implicit-swift-modules \
+// RUN:   -external-plugin-path %t/plugins/#%swift-plugin-server \
+// RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import \
+// RUN:   -module-name MyApp -explicit-swift-module-map-file @%t/map.casid \
+// RUN:   %s @%t/MyApp.cmd
+
+@attached(extension, conformances: P, names: named(requirement))
+macro DelegatedConformance() = #externalMacro(module: "MacroDefinition", type: "DelegatedConformanceViaExtensionMacro")
+
+protocol P {
+  static func requirement()
+}
+
+struct Wrapped: P {
+  static func requirement() {
+    print("Wrapped.requirement")
+  }
+}
+
+@DelegatedConformance
+struct Generic<Element> {}
+
+// CHECK: {"expandMacroResult":{"diagnostics":[],"expandedSource":"extension Generic: P where Element: P {\n  static func requirement() {\n    Element.requirement()\n  }\n}"}}
+
+func requiresP(_ value: (some P).Type) {
+  value.requirement()
+}
+
+requiresP(Generic<Wrapped>.self)
+
+struct Outer {
+  @DelegatedConformance
+  struct Nested<Element> {}
+}
+
+// CHECK: {"expandMacroResult":{"diagnostics":[],"expandedSource":"extension Outer.Nested: P where Element: P {\n  static func requirement() {\n    Element.requirement()\n  }\n}"}}
+
+requiresP(Outer.Nested<Wrapped>.self)
diff --git a/test/CAS/module_deps.swift b/test/CAS/module_deps.swift
index be04d1236b09d..fd2957394c6df 100644
--- a/test/CAS/module_deps.swift
+++ b/test/CAS/module_deps.swift
@@ -4,7 +4,7 @@
 // RUN: mkdir -p %t/clang-module-cache
 // RUN: mkdir -p %t/cas
 
-// RUN: %target-swift-frontend -scan-dependencies -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/../ScanDependencies/Inputs/CHeaders -I %S/../ScanDependencies/Inputs/Swift -emit-dependencies -emit-dependencies-path %t/deps.d -import-objc-header %S/../ScanDependencies/Inputs/CHeaders/Bridging.h -swift-version 4 -cache-compile-job -cas-path %t/cas -no-clang-include-tree
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/../ScanDependencies/Inputs/CHeaders -I %S/../ScanDependencies/Inputs/Swift -emit-dependencies -emit-dependencies-path %t/deps.d -import-objc-header %S/../ScanDependencies/Inputs/CHeaders/Bridging.h -swift-version 4 -cache-compile-job -cas-path %t/cas -no-clang-include-tree
 // Check the contents of the JSON output
 // RUN: %validate-json %t/deps.json &>/dev/null
 // RUN: %FileCheck -check-prefix CHECK -check-prefix CHECK_NO_CLANG_TARGET %s < %t/deps.json
@@ -15,12 +15,12 @@
 // Check the make-style dependencies file
 // RUN: %FileCheck %s -check-prefix CHECK-MAKE-DEPS < %t/deps.d
 
-// RUN: %target-swift-frontend -scan-dependencies -test-dependency-scan-cache-serialization -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/../ScanDependencies/Inputs/CHeaders -I %S/../ScanDependencies/Inputs/Swift -import-objc-header %S/../ScanDependencies/Inputs/CHeaders/Bridging.h -swift-version 4 -cache-compile-job -cas-path %t/cas -no-clang-include-tree
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -test-dependency-scan-cache-serialization -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/../ScanDependencies/Inputs/CHeaders -I %S/../ScanDependencies/Inputs/Swift -import-objc-header %S/../ScanDependencies/Inputs/CHeaders/Bridging.h -swift-version 4 -cache-compile-job -cas-path %t/cas -no-clang-include-tree
 // RUN: %validate-json %t/deps.json &>/dev/null
 // RUN: %FileCheck -check-prefix CHECK -check-prefix CHECK_NO_CLANG_TARGET %s < %t/deps.json
 
 // Ensure that scanning with `-clang-target` makes sure that Swift modules' respective PCM-dependency-build-argument sets do not contain target triples.
-// RUN: %target-swift-frontend -scan-dependencies -module-cache-path %t/clang-module-cache %s -o %t/deps_clang_target.json -I %S/../ScanDependencies/Inputs/CHeaders -I %S/../ScanDependencies/Inputs/Swift -import-objc-header %S/../ScanDependencies/Inputs/CHeaders/Bridging.h -swift-version 4 -clang-target %target-cpu-apple-macosx10.14 -cache-compile-job -cas-path %t/cas -no-clang-include-tree
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -module-cache-path %t/clang-module-cache %s -o %t/deps_clang_target.json -I %S/../ScanDependencies/Inputs/CHeaders -I %S/../ScanDependencies/Inputs/Swift -import-objc-header %S/../ScanDependencies/Inputs/CHeaders/Bridging.h -swift-version 4 -clang-target %target-cpu-apple-macosx10.14 -cache-compile-job -cas-path %t/cas -no-clang-include-tree
 // Check the contents of the JSON output
 // RUN: %validate-json %t/deps_clang_target.json &>/dev/null
 // RUN: %FileCheck -check-prefix CHECK_CLANG_TARGET %s < %t/deps_clang_target.json
diff --git a/test/CAS/module_deps_include_tree.swift b/test/CAS/module_deps_include_tree.swift
index b20c3e3a1f580..9800c30080cf5 100644
--- a/test/CAS/module_deps_include_tree.swift
+++ b/test/CAS/module_deps_include_tree.swift
@@ -4,7 +4,7 @@
 // RUN: mkdir -p %t/clang-module-cache
 // RUN: mkdir -p %t/cas
 
-// RUN: %target-swift-frontend -scan-dependencies -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/../ScanDependencies/Inputs/CHeaders -I %S/../ScanDependencies/Inputs/Swift -emit-dependencies -emit-dependencies-path %t/deps.d -import-objc-header %S/../ScanDependencies/Inputs/CHeaders/Bridging.h -swift-version 4 -cache-compile-job -cas-path %t/cas
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/../ScanDependencies/Inputs/CHeaders -I %S/../ScanDependencies/Inputs/Swift -emit-dependencies -emit-dependencies-path %t/deps.d -import-objc-header %S/../ScanDependencies/Inputs/CHeaders/Bridging.h -swift-version 4 -cache-compile-job -cas-path %t/cas
 // Check the contents of the JSON output
 // RUN: %validate-json %t/deps.json &>/dev/null
 // RUN: %FileCheck -check-prefix CHECK -check-prefix CHECK_NO_CLANG_TARGET %s < %t/deps.json
@@ -15,12 +15,12 @@
 // Check the make-style dependencies file
 // RUN: %FileCheck %s -check-prefix CHECK-MAKE-DEPS < %t/deps.d
 
-// RUN: %target-swift-frontend -scan-dependencies -test-dependency-scan-cache-serialization -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/../ScanDependencies/Inputs/CHeaders -I %S/../ScanDependencies/Inputs/Swift -import-objc-header %S/../ScanDependencies/Inputs/CHeaders/Bridging.h -swift-version 4 -cache-compile-job -cas-path %t/cas
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -test-dependency-scan-cache-serialization -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/../ScanDependencies/Inputs/CHeaders -I %S/../ScanDependencies/Inputs/Swift -import-objc-header %S/../ScanDependencies/Inputs/CHeaders/Bridging.h -swift-version 4 -cache-compile-job -cas-path %t/cas
 // RUN: %validate-json %t/deps.json &>/dev/null
 // RUN: %FileCheck -check-prefix CHECK -check-prefix CHECK_NO_CLANG_TARGET %s < %t/deps.json
 
 // Ensure that scanning with `-clang-target` makes sure that Swift modules' respective PCM-dependency-build-argument sets do not contain target triples.
-// RUN: %target-swift-frontend -scan-dependencies -module-cache-path %t/clang-module-cache %s -o %t/deps_clang_target.json -I %S/../ScanDependencies/Inputs/CHeaders -I %S/../ScanDependencies/Inputs/Swift -import-objc-header %S/../ScanDependencies/Inputs/CHeaders/Bridging.h -swift-version 4 -clang-target %target-cpu-apple-macosx10.14 -cache-compile-job -cas-path %t/cas
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -module-cache-path %t/clang-module-cache %s -o %t/deps_clang_target.json -I %S/../ScanDependencies/Inputs/CHeaders -I %S/../ScanDependencies/Inputs/Swift -import-objc-header %S/../ScanDependencies/Inputs/CHeaders/Bridging.h -swift-version 4 -clang-target %target-cpu-apple-macosx10.14 -cache-compile-job -cas-path %t/cas
 // Check the contents of the JSON output
 // RUN: %validate-json %t/deps_clang_target.json &>/dev/null
 // RUN: %FileCheck -check-prefix CHECK_CLANG_TARGET %s < %t/deps_clang_target.json
diff --git a/test/CAS/module_hash.swift b/test/CAS/module_hash.swift
index 2a8e0c250b9bd..4272bb24cb88f 100644
--- a/test/CAS/module_hash.swift
+++ b/test/CAS/module_hash.swift
@@ -1,9 +1,9 @@
 // RUN: %empty-directory(%t)
 // RUN: mkdir -p %t/clang-module-cache
 
-// RUN: %target-swift-frontend -scan-dependencies -module-cache-path %t/clang-module-cache %s -o %t/deps.json -module-name Test
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -module-cache-path %t/clang-module-cache %s -o %t/deps.json -module-name Test
 
-// RUN: %target-swift-frontend -scan-dependencies -module-cache-path %t/clang-module-cache %s -o %t/deps_cache.json -module-name Test \
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -module-cache-path %t/clang-module-cache %s -o %t/deps_cache.json -module-name Test \
 // RUN:    -cache-compile-job -cas-path %t/cas
 
 // RUN: %{python} %S/Inputs/SwiftDepsExtractor.py %t/deps.json Swift modulePath > %t/path1
diff --git a/test/CAS/plugin_cas.swift b/test/CAS/plugin_cas.swift
index 9a689b755e04b..a31f66b071f6f 100644
--- a/test/CAS/plugin_cas.swift
+++ b/test/CAS/plugin_cas.swift
@@ -4,7 +4,7 @@
 // RUN: mkdir -p %t/clang-module-cache
 // RUN: mkdir -p %t/cas
 
-// RUN: %target-swift-frontend -scan-dependencies -module-cache-path %t/clang-module-cache %s \
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -module-cache-path %t/clang-module-cache %s \
 // RUN:   -o %t/deps.json -I %S/../ScanDependencies/Inputs/CHeaders -I %S/../ScanDependencies/Inputs/Swift \
 // RUN:   -emit-dependencies -emit-dependencies-path %t/deps.d -import-objc-header %S/../ScanDependencies/Inputs/CHeaders/Bridging.h \
 // RUN:   -swift-version 4 -cache-compile-job \
@@ -23,7 +23,7 @@
 // RUN: %FileCheck %s -check-prefix CHECK-MAKE-DEPS < %t/deps.d
 
 // Ensure that scanning with `-clang-target` makes sure that Swift modules' respective PCM-dependency-build-argument sets do not contain target triples.
-// RUN: %target-swift-frontend -scan-dependencies -module-cache-path %t/clang-module-cache %s \
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -module-cache-path %t/clang-module-cache %s \
 // RUN:   -o %t/deps_clang_target.json -I %S/../ScanDependencies/Inputs/CHeaders \
 // RUN:   -I %S/../ScanDependencies/Inputs/Swift -import-objc-header %S/../ScanDependencies/Inputs/CHeaders/Bridging.h \
 // RUN:   -swift-version 4 -clang-target %target-cpu-apple-macosx10.14 -cache-compile-job \
diff --git a/test/Frontend/module-alias-scan-deps.swift b/test/Frontend/module-alias-scan-deps.swift
index bf313ed52f280..a22c74411b0af 100644
--- a/test/Frontend/module-alias-scan-deps.swift
+++ b/test/Frontend/module-alias-scan-deps.swift
@@ -11,7 +11,7 @@
 // RUN: test -f %t/AppleLogging.swiftmodule
 
 /// Scanned dependencies should contain real name AppleLogging
-// RUN: %target-swift-frontend -scan-dependencies  %t/FileLib.swift -module-alias XLogging=AppleLogging -I %t > %t/scandump.output
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface  %t/FileLib.swift -module-alias XLogging=AppleLogging -I %t > %t/scandump.output
 // RUN: %validate-json %t/scandump.output | %FileCheck %s -check-prefix=CHECK-REAL-NAME
 // CHECK-REAL-NAME-NOT: "swiftPrebuiltExternal": "XLogging"
 // CHECK-REAL-NAME-NOT: "compiledModulePath":{{.*}}XLogging.swiftmodule",
@@ -24,7 +24,7 @@
 // RUN: test -f %t/AppleLoggingIF.swiftinterface
 
 /// Scanned dependencies should contain real name AppleLoggingIF
-// RUN: %target-swift-frontend -scan-dependencies  %t/FileLib.swift -module-alias XLogging=AppleLoggingIF -I %t > %t/scandumpIF.output
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface  %t/FileLib.swift -module-alias XLogging=AppleLoggingIF -I %t > %t/scandumpIF.output
 // RUN: %validate-json %t/scandumpIF.output | %FileCheck %s -check-prefix=CHECK-REAL-NAME-IF
 // CHECK-REAL-NAME-IF-NOT: "swift": "XLogging"
 // CHECK-REAL-NAME-IF-NOT: "moduleInterfacePath":{{.*}}XLogging.swiftinterface
diff --git a/test/ModuleInterface/clang-args-transitive-availability.swift b/test/ModuleInterface/clang-args-transitive-availability.swift
index bdfb692fd3cee..dfc4df497cb38 100644
--- a/test/ModuleInterface/clang-args-transitive-availability.swift
+++ b/test/ModuleInterface/clang-args-transitive-availability.swift
@@ -5,7 +5,7 @@
 // received the TANGERINE macro
 // RUN: %target-swift-frontend -typecheck -strict-implicit-module-context %s -I %S/Inputs/macro-only-module -Xcc -DTANGERINE=1 -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import
 
-// RUN: %target-swift-frontend -scan-dependencies -strict-implicit-module-context %s -o %t/deps.json -I %S/Inputs/macro-only-module -Xcc -DTANGERINE=1 -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -strict-implicit-module-context %s -o %t/deps.json -I %S/Inputs/macro-only-module -Xcc -DTANGERINE=1 -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import
 // RUN: %validate-json %t/deps.json &>/dev/null
 // RUN: %FileCheck %s < %t/deps.json
 
diff --git a/test/ModuleInterface/clang-session-transitive.swift b/test/ModuleInterface/clang-session-transitive.swift
index ae6ef6e6ef4df..8bf1cd8314245 100644
--- a/test/ModuleInterface/clang-session-transitive.swift
+++ b/test/ModuleInterface/clang-session-transitive.swift
@@ -4,7 +4,7 @@
 
 // RUN: %target-build-swift -module-name TestModule -module-link-name TestModule %S/Inputs/TestModule.swift -enable-library-evolution -emit-module-interface -o %t/TestModule.swiftmodule -swift-version 5 -Xfrontend -disable-implicit-concurrency-module-import -Xfrontend -disable-implicit-string-processing-module-import
 
-// RUN: %target-swift-frontend -scan-dependencies %s -o %t/deps.json -I%t -validate-clang-modules-once -clang-build-session-file %t/Build.session -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import
+// RUN: %target-swift-frontend -scan-dependencies -no-scanner-module-validation %s -o %t/deps.json -I%t -validate-clang-modules-once -clang-build-session-file %t/Build.session -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import
 // RUN: %validate-json %t/deps.json &>/dev/null
 // RUN: %FileCheck %s < %t/deps.json
 
diff --git a/test/ModuleInterface/extension-transitive-availability.swift b/test/ModuleInterface/extension-transitive-availability.swift
index 318986238f24a..a677fc4d6292c 100644
--- a/test/ModuleInterface/extension-transitive-availability.swift
+++ b/test/ModuleInterface/extension-transitive-availability.swift
@@ -3,7 +3,7 @@
 
 // RUN: %target-swift-emit-module-interface(%t/ExtensionAvailable.swiftinterface) %S/Inputs/extension-available.swift -module-name ExtensionAvailable -I%t -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import
 
-// RUN: %target-swift-frontend -scan-dependencies %s -o %t/deps.json -I%t -application-extension -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import
+// RUN: %target-swift-frontend -scan-dependencies -no-scanner-module-validation %s -o %t/deps.json -I%t -application-extension -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import
 // RUN: %validate-json %t/deps.json &>/dev/null
 // RUN: %FileCheck %s < %t/deps.json
 
diff --git a/test/ModuleInterface/infer-arch-from-file.swift b/test/ModuleInterface/infer-arch-from-file.swift
index ab1e409401a13..f75771843269c 100644
--- a/test/ModuleInterface/infer-arch-from-file.swift
+++ b/test/ModuleInterface/infer-arch-from-file.swift
@@ -5,7 +5,7 @@
 
 import arm64
 
-// RUN: %target-swift-frontend -scan-dependencies %s -o %t/deps.json -I %t -target arm64-apple-macos11.0
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface %s -o %t/deps.json -I %t -target arm64-apple-macos11.0
 // RUN: %validate-json %t/deps.json | %FileCheck %s
 
 // CHECK-NOT: arm64e-apple-macos11.0
diff --git a/test/ScanDependencies/FilterClangSearchPaths.swift b/test/ScanDependencies/FilterClangSearchPaths.swift
index e8fdf399e224a..45563dd4c8506 100644
--- a/test/ScanDependencies/FilterClangSearchPaths.swift
+++ b/test/ScanDependencies/FilterClangSearchPaths.swift
@@ -1,7 +1,7 @@
 // RUN: %empty-directory(%t)
 // RUN: %empty-directory(%t/clang-module-cache)
 
-// RUN: %target-swift-frontend -scan-dependencies -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -Xcc -fobjc-disable-direct-methods-for-testing -Xcc -I -Xcc /tmp/foo -Xcc -I/tmp/bar
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -Xcc -fobjc-disable-direct-methods-for-testing -Xcc -I -Xcc /tmp/foo -Xcc -I/tmp/bar
 // Check the contents of the JSON output
 // RUN: %validate-json %t/deps.json | %FileCheck %s
 
diff --git a/test/ScanDependencies/ObjCStrict.swift b/test/ScanDependencies/ObjCStrict.swift
index 5ba108d5fabed..c5764b7c7a1f1 100644
--- a/test/ScanDependencies/ObjCStrict.swift
+++ b/test/ScanDependencies/ObjCStrict.swift
@@ -1,7 +1,7 @@
 // RUN: %empty-directory(%t)
 // RUN: %empty-directory(%t/clang-module-cache)
 
-// RUN: %target-swift-frontend -scan-dependencies -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -Xcc -fobjc-disable-direct-methods-for-testing
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -Xcc -fobjc-disable-direct-methods-for-testing
 // Check the contents of the JSON output
 // RUN: %validate-json %t/deps.json | %FileCheck %s
 
diff --git a/test/ScanDependencies/batch_module_scan.swift b/test/ScanDependencies/batch_module_scan.swift
index e276fda317883..6c4714e5612bc 100644
--- a/test/ScanDependencies/batch_module_scan.swift
+++ b/test/ScanDependencies/batch_module_scan.swift
@@ -14,7 +14,7 @@
 // RUN: echo "\"output\": \"%/t/outputs/F.pcm.json\"" >> %/t/inputs/input.json
 // RUN: echo "}]" >> %/t/inputs/input.json
 
-// RUN: %target-swift-frontend -scan-dependencies -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -emit-dependencies -emit-dependencies-path %t/deps.d -import-objc-header %S/Inputs/CHeaders/Bridging.h -swift-version 4 -batch-scan-input-file %/t/inputs/input.json
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -emit-dependencies -emit-dependencies-path %t/deps.d -import-objc-header %S/Inputs/CHeaders/Bridging.h -swift-version 4 -batch-scan-input-file %/t/inputs/input.json
 
 // Check the contents of the JSON output
 // RUN: %validate-json %t/outputs/F.pcm.json | %FileCheck %s -check-prefix=CHECK-PCM
diff --git a/test/ScanDependencies/bin_mod_import.swift b/test/ScanDependencies/bin_mod_import.swift
index bf4ad63e4673f..79a04013891e8 100644
--- a/test/ScanDependencies/bin_mod_import.swift
+++ b/test/ScanDependencies/bin_mod_import.swift
@@ -7,11 +7,11 @@ import EWrapper
 // Step 1: Build a swift interface into a binary module
 // RUN: %target-swift-frontend -compile-module-from-interface %S/Inputs/Swift/EWrapper.swiftinterface -o %t/EWrapper.swiftmodule -I %t
 // Step 3: scan dependency should give us the binary module and a textual swift dependency from it
-// RUN: %target-swift-frontend -scan-dependencies %s -o %t/deps.json -I %t
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface %s -o %t/deps.json -I %t
 // RUN: %validate-json %t/deps.json | %FileCheck %s
 
 // Step 4: Ensure that round-trip serialization does not affect result
-// RUN: %target-swift-frontend -scan-dependencies -test-dependency-scan-cache-serialization %s -o %t/deps.json -I %t
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -test-dependency-scan-cache-serialization %s -o %t/deps.json -I %t
 // RUN: %validate-json %t/deps.json | %FileCheck %s
 
 // CHECK: "modulePath": "{{.*}}EWrapper.swiftmodule"
diff --git a/test/ScanDependencies/blocklist-path-pass-down.swift b/test/ScanDependencies/blocklist-path-pass-down.swift
index 0136ddf9cefe7..bd7c40efb128c 100644
--- a/test/ScanDependencies/blocklist-path-pass-down.swift
+++ b/test/ScanDependencies/blocklist-path-pass-down.swift
@@ -14,7 +14,7 @@
 
 
 // Run the scan
-// RUN: %target-swift-frontend -scan-dependencies %s -o %t/deps.json -F %t/Frameworks/ -sdk %t -blocklist-file %t/blocklist.yml
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface %s -o %t/deps.json -F %t/Frameworks/ -sdk %t -blocklist-file %t/blocklist.yml
 // RUN: %validate-json %t/deps.json | %FileCheck %s
 
 import E
diff --git a/test/ScanDependencies/bridging_header_dep_module_map.swift b/test/ScanDependencies/bridging_header_dep_module_map.swift
index ac17bfba27eb8..7c14b3e40afd9 100644
--- a/test/ScanDependencies/bridging_header_dep_module_map.swift
+++ b/test/ScanDependencies/bridging_header_dep_module_map.swift
@@ -20,7 +20,7 @@
 
 // - Scan main module and ensure that the "FooClient" recipe includes the modulemap for Foo's briding header's module dependencies
 // but not other dependencies
-// RUN: %target-swift-frontend -scan-dependencies %t/bridging_header_dep_module_map.swift -I %t/FooModuleDir -I %t/TestSwiftInterfaces -I %t/TestCHeaders -I %S/Inputs/CHeaders -o %t/deps.json
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface %t/bridging_header_dep_module_map.swift -I %t/FooModuleDir -I %t/TestSwiftInterfaces -I %t/TestCHeaders -I %S/Inputs/CHeaders -o %t/deps.json
 // RUN: %validate-json %t/deps.json | %FileCheck %s
 
 // Given the following dependency graph:
diff --git a/test/ScanDependencies/can_import_placeholder.swift b/test/ScanDependencies/can_import_placeholder.swift
index c7400bccc4611..9a42e2b9a04a2 100644
--- a/test/ScanDependencies/can_import_placeholder.swift
+++ b/test/ScanDependencies/can_import_placeholder.swift
@@ -10,11 +10,11 @@
 // RUN: echo "\"isFramework\": false" >> %/t/inputs/map.json
 // RUN: echo "}]" >> %/t/inputs/map.json
 
-// RUN: %target-swift-frontend -scan-dependencies -module-cache-path %t/clang-module-cache %s -placeholder-dependency-module-map-file %t/inputs/map.json -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -emit-dependencies -emit-dependencies-path %t/deps.d -import-objc-header %S/Inputs/CHeaders/Bridging.h -swift-version 4
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -module-cache-path %t/clang-module-cache %s -placeholder-dependency-module-map-file %t/inputs/map.json -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -emit-dependencies -emit-dependencies-path %t/deps.d -import-objc-header %S/Inputs/CHeaders/Bridging.h -swift-version 4
 // RUN: %validate-json %t/deps.json | %FileCheck %s
 
 // Ensure that round-trip serialization does not affect result
-// RUN: %target-swift-frontend -scan-dependencies -test-dependency-scan-cache-serialization -module-cache-path %t/clang-module-cache %s -placeholder-dependency-module-map-file %t/inputs/map.json -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -emit-dependencies -emit-dependencies-path %t/deps.d -import-objc-header %S/Inputs/CHeaders/Bridging.h -swift-version 4
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -test-dependency-scan-cache-serialization -module-cache-path %t/clang-module-cache %s -placeholder-dependency-module-map-file %t/inputs/map.json -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -emit-dependencies -emit-dependencies-path %t/deps.d -import-objc-header %S/Inputs/CHeaders/Bridging.h -swift-version 4
 // RUN: %validate-json %t/deps.json | %FileCheck %s
 
 // REQUIRES: executable_test
diff --git a/test/ScanDependencies/clang-target.swift b/test/ScanDependencies/clang-target.swift
index 5bfaf3601b8cd..3c0170b80a251 100644
--- a/test/ScanDependencies/clang-target.swift
+++ b/test/ScanDependencies/clang-target.swift
@@ -12,7 +12,7 @@
 
 // With -clang-target, we build one X.pcm
 // RUN: find %t.module-cache -name "X-*.pcm" | count 1
-// RUN: %target-swift-frontend -scan-dependencies -module-cache-path %t.module-cache %s -o %t.deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -target %target-cpu-apple-macosx10.14 -clang-target %target-cpu-apple-macosx10.14
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -module-cache-path %t.module-cache %s -o %t.deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -target %target-cpu-apple-macosx10.14 -clang-target %target-cpu-apple-macosx10.14
 
 // RUN: %validate-json %t.deps.json | %FileCheck %s
 
diff --git a/test/ScanDependencies/clang_auxiliary_module_framework.swift b/test/ScanDependencies/clang_auxiliary_module_framework.swift
index 0c3448ce00c71..5154fdd85e5cb 100644
--- a/test/ScanDependencies/clang_auxiliary_module_framework.swift
+++ b/test/ScanDependencies/clang_auxiliary_module_framework.swift
@@ -1,11 +1,11 @@
 // REQUIRES: OS=macosx
 // RUN: %empty-directory(%t)
-// RUN: %target-swift-frontend -scan-dependencies %s -o %t/deps.json -emit-dependencies -emit-dependencies-path %t/deps.d -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import -F %S/Inputs/Frameworks -verify
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface %s -o %t/deps.json -emit-dependencies -emit-dependencies-path %t/deps.d -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import -F %S/Inputs/Frameworks -verify
 // Check the contents of the JSON output
 // RUN: %validate-json %t/deps.json | %FileCheck %s
 
 // Ensure that round-trip serialization does not affect result
-// RUN: %target-swift-frontend -scan-dependencies -test-dependency-scan-cache-serialization %s -o %t/deps.json -emit-dependencies -emit-dependencies-path %t/deps.d -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import -F %S/Inputs/Frameworks -verify
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -test-dependency-scan-cache-serialization %s -o %t/deps.json -emit-dependencies -emit-dependencies-path %t/deps.d -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import -F %S/Inputs/Frameworks -verify
 // RUN: %validate-json %t/deps.json | %FileCheck %s
 
 import WithAuxClangModule
diff --git a/test/ScanDependencies/compiled_swift_modules.swift b/test/ScanDependencies/compiled_swift_modules.swift
index d4bb2864dd23f..4ccda3f788fc1 100644
--- a/test/ScanDependencies/compiled_swift_modules.swift
+++ b/test/ScanDependencies/compiled_swift_modules.swift
@@ -8,32 +8,46 @@ import Foo
 // HAS_COMPILED: "compiledModuleCandidates": [
 // HAS_COMPILED-NEXT: "{{.*}}Foo.swiftmodule{{.*}}.swiftmodule"
 
+// HAS_BINARY: "swiftPrebuiltExternal": "Foo"
+
 // HAS_NO_COMPILED-NOT: "{{.*}}Foo.swiftmodule{{.*}}.swiftmodule"
 
 // Step 1: build swift interface and swift module side by side
 // RUN: %target-swift-frontend -emit-module %t/Foo.swift -emit-module-path %t/Foo.swiftmodule/%target-swiftmodule-name -module-name Foo -emit-module-interface-path %t/Foo.swiftmodule/%target-swiftinterface-name
 
 // Step 2: scan dependency should give us the binary module adjacent to the interface file.
-// RUN: %target-swift-frontend -scan-dependencies %s -o %t/deps.json -I %t -emit-dependencies -emit-dependencies-path %t/deps.d
+// RUN: %target-swift-frontend -scan-dependencies -no-scanner-module-validation %s -o %t/deps.json -I %t -emit-dependencies -emit-dependencies-path %t/deps.d
 // RUN: %validate-json %t/deps.json | %FileCheck %s -check-prefix=HAS_COMPILED
 
+/// Check scanner picked binary dependency if not requesting raw scan output.
+// RUN: %target-swift-frontend -scan-dependencies %s -o %t/deps.json -I %t -emit-dependencies -emit-dependencies-path %t/deps.d
+// RUN: %validate-json %t/deps.json | %FileCheck %s -check-prefix=HAS_BINARY
+
 // Step 3: remove the adjacent module.
 // RUN: rm %t/Foo.swiftmodule/%target-swiftmodule-name
 
 // Step 4: scan dependency should give us the interface file.
-// RUN: %target-swift-frontend -scan-dependencies %s -o %t/deps.json -I %t -emit-dependencies -emit-dependencies-path %t/deps.d
+// RUN: %target-swift-frontend -scan-dependencies -no-scanner-module-validation %s -o %t/deps.json -I %t -emit-dependencies -emit-dependencies-path %t/deps.d
 // RUN: %validate-json %t/deps.json | %FileCheck %s -check-prefix=HAS_NO_COMPILED
 
 // Step 4: build prebuilt module cache using the interface.
 // RUN: %target-swift-frontend -compile-module-from-interface -o %t/ResourceDir/%target-sdk-name/prebuilt-modules/Foo.swiftmodule/%target-swiftmodule-name -module-name Foo -disable-interface-lock %t/Foo.swiftmodule/%target-swiftinterface-name
 
 // Step 5: scan dependency now should give us the prebuilt module cache
-// RUN: %target-swift-frontend -scan-dependencies %s -o %t/deps.json -I %t -emit-dependencies -emit-dependencies-path %t/deps.d -sdk %t -prebuilt-module-cache-path %t/ResourceDir/%target-sdk-name/prebuilt-modules
+// RUN: %target-swift-frontend -scan-dependencies -no-scanner-module-validation %s -o %t/deps.json -I %t -emit-dependencies -emit-dependencies-path %t/deps.d -sdk %t -prebuilt-module-cache-path %t/ResourceDir/%target-sdk-name/prebuilt-modules
 // RUN: %validate-json %t/deps.json | %FileCheck %s -check-prefix=HAS_COMPILED
 
+/// Check scanner picked binary dependency if not requesting raw scan output.
+// RUN: %target-swift-frontend -scan-dependencies %s -o %t/deps.json -I %t -emit-dependencies -emit-dependencies-path %t/deps.d -sdk %t -prebuilt-module-cache-path %t/ResourceDir/%target-sdk-name/prebuilt-modules
+// RUN: %validate-json %t/deps.json | %FileCheck %s -check-prefix=HAS_BINARY
+
 // Step 6: update the interface file from where the prebuilt module cache was built.
 // RUN: touch %t/Foo.swiftmodule/%target-swiftinterface-name
 
 // Step 7: scan dependency should give us the prebuilt module file even though it's out-of-date.
-// RUN: %target-swift-frontend -scan-dependencies %s -o %t/deps.json -I %t -emit-dependencies -emit-dependencies-path %t/deps.d -sdk %t -prebuilt-module-cache-path %t/ResourceDir/%target-sdk-name/prebuilt-modules
+// RUN: %target-swift-frontend -scan-dependencies -no-scanner-module-validation %s -o %t/deps.json -I %t -emit-dependencies -emit-dependencies-path %t/deps.d -sdk %t -prebuilt-module-cache-path %t/ResourceDir/%target-sdk-name/prebuilt-modules
 // RUN: %validate-json %t/deps.json | %FileCheck %s -check-prefix=HAS_COMPILED
+
+// Step 8: The new scanner behavior should not give use prebuilt module file because it is out-of-date.
+// RUN: %target-swift-frontend -scan-dependencies %s -o %t/deps.json -I %t -emit-dependencies -emit-dependencies-path %t/deps.d -sdk %t -prebuilt-module-cache-path %t/ResourceDir/%target-sdk-name/prebuilt-modules
+// RUN: %validate-json %t/deps.json | %FileCheck %s -check-prefix=HAS_NO_COMPILED
diff --git a/test/ScanDependencies/direct_cc1_scan.swift b/test/ScanDependencies/direct_cc1_scan.swift
index 996fdec35832b..5888db7a9bd2f 100644
--- a/test/ScanDependencies/direct_cc1_scan.swift
+++ b/test/ScanDependencies/direct_cc1_scan.swift
@@ -7,13 +7,13 @@
 // RUN:   -emit-module-interface-path %t/A.swiftinterface \
 // RUN:   -o %t/A.swiftmodule
 
-// RUN: %target-swift-frontend -scan-dependencies -o %t/deps.json -I %t \
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -o %t/deps.json -I %t \
 // RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import -parse-stdlib \
 // RUN:   %t/test.swift -module-name Test -swift-version 5
 // RUN: %{python} %S/../CAS/Inputs/BuildCommandExtractor.py %t/deps.json A | %FileCheck %s --check-prefix CHECK-NO-DIRECT-CC1
 // RUN: %{python} %S/../CAS/Inputs/BuildCommandExtractor.py %t/deps.json Test | %FileCheck %s --allow-empty --check-prefix CHECK-NO-DIRECT-CC1
 
-// RUN: %target-swift-frontend -scan-dependencies -o %t/deps2.json -I %t \
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -o %t/deps2.json -I %t \
 // RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import -parse-stdlib \
 // RUN:   -g -file-compilation-dir %t -Xcc -ferror-limit=1 \
 // RUN:   %t/test.swift -module-name Test -swift-version 5 -experimental-clang-importer-direct-cc1-scan
diff --git a/test/ScanDependencies/eliminate_unused_vfs.swift b/test/ScanDependencies/eliminate_unused_vfs.swift
index 7e5b88cff8ec2..dc2a9909595ec 100644
--- a/test/ScanDependencies/eliminate_unused_vfs.swift
+++ b/test/ScanDependencies/eliminate_unused_vfs.swift
@@ -6,7 +6,7 @@
 
 // RUN: sed -e "s|OUT_DIR|%t/redirects|g"  -e "s|IN_DIR|%S/Inputs/CHeaders|g" %t/overlay_template.yaml > %t/overlay.yaml
 
-// RUN: %target-swift-frontend -scan-dependencies -module-cache-path %t/module-cache %t/test.swift -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import -Xcc -ivfsoverlay -Xcc %t/overlay.yaml
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -module-cache-path %t/module-cache %t/test.swift -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import -Xcc -ivfsoverlay -Xcc %t/overlay.yaml
 // RUN: %validate-json %t/deps.json | %FileCheck %s
 
 //--- overlay_template.yaml
diff --git a/test/ScanDependencies/explicit-swift-dependencies.swift b/test/ScanDependencies/explicit-swift-dependencies.swift
index 746bf7f8416bf..e5a281caec5a0 100644
--- a/test/ScanDependencies/explicit-swift-dependencies.swift
+++ b/test/ScanDependencies/explicit-swift-dependencies.swift
@@ -1,7 +1,7 @@
 // RUN: %empty-directory(%t)
 // RUN: mkdir -p %t/clang-module-cache
 
-// RUN: %target-swift-frontend -scan-dependencies -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -emit-dependencies -emit-dependencies-path %t/deps.d -import-objc-header %S/Inputs/CHeaders/Bridging.h -swift-version 4
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -emit-dependencies -emit-dependencies-path %t/deps.d -import-objc-header %S/Inputs/CHeaders/Bridging.h -swift-version 4
 // Check the contents of the JSON output
 // RUN: %validate-json %t/deps.json | %FileCheck %s
 
diff --git a/test/ScanDependencies/header_deps_of_binary.swift b/test/ScanDependencies/header_deps_of_binary.swift
index 20b43c3343925..d1c6e2b830ca8 100644
--- a/test/ScanDependencies/header_deps_of_binary.swift
+++ b/test/ScanDependencies/header_deps_of_binary.swift
@@ -23,7 +23,7 @@
 // RUN: %target-swift-frontend -emit-module -emit-module-path %t/SwiftModules/Foo.swiftmodule %t/foo.swift -module-name Foo -import-objc-header %t/PCH/foo.pch -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import -disable-implicit-swift-modules -explicit-swift-module-map-file %t/map.json
 
 // - Scan main module and ensure that the header dependencies point to .h and not .pch file
-// RUN: %target-swift-frontend -scan-dependencies %t/header_deps_of_binary.swift -I %t/SwiftModules -I %S/Inputs/Swift -I %S/Inputs/CHeaders -o %t/deps.json
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface %t/header_deps_of_binary.swift -I %t/SwiftModules -I %S/Inputs/Swift -I %S/Inputs/CHeaders -o %t/deps.json
 // RUN: %validate-json %t/deps.json | %FileCheck %s
 
 // CHECK: "swift": "FooClient"
diff --git a/test/ScanDependencies/include-sdk-in-command.swift b/test/ScanDependencies/include-sdk-in-command.swift
index 1f1d96e1ec7bf..84512632a0b25 100644
--- a/test/ScanDependencies/include-sdk-in-command.swift
+++ b/test/ScanDependencies/include-sdk-in-command.swift
@@ -1,6 +1,6 @@
 // RUN: %empty-directory(%t)
 
-// RUN: %target-swift-frontend -scan-dependencies %s -o %t/deps.json -sdk %t/mysecretsdk.sdk
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface %s -o %t/deps.json -sdk %t/mysecretsdk.sdk
 
 // Check the contents of the JSON output
 // RUN: %validate-json %t/deps.json | %FileCheck %s
diff --git a/test/ScanDependencies/module_deps_binary_dep_swift_overlay.swift b/test/ScanDependencies/module_deps_binary_dep_swift_overlay.swift
index 75c70287c7cb1..8814a95ecfb3b 100644
--- a/test/ScanDependencies/module_deps_binary_dep_swift_overlay.swift
+++ b/test/ScanDependencies/module_deps_binary_dep_swift_overlay.swift
@@ -8,7 +8,7 @@
 // RUN: %target-swift-frontend -emit-module -emit-module-path %t/DependencyModules/BinaryModuleDep.swiftmodule -module-cache-path %t/clang-module-cache %t/BinaryModuleDepSource.swift -module-name BinaryModuleDep -I %S/Inputs/CHeaders -I %S/Inputs/Swift
 
 // Scan the client and ensure both the Client and BinaryModuleDep modules have a Swift overlay dependency on 'F' as imported by 'ClangModuleWithOverlayedDep'
-// RUN: %target-swift-frontend -scan-dependencies -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -I %t/DependencyModules
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -I %t/DependencyModules
 // Check the contents of the JSON output
 // RUN: %validate-json %t/deps.json | %FileCheck %s
 
diff --git a/test/ScanDependencies/module_deps_cache_reuse.swift b/test/ScanDependencies/module_deps_cache_reuse.swift
index 4012e5d406597..51718ede38662 100644
--- a/test/ScanDependencies/module_deps_cache_reuse.swift
+++ b/test/ScanDependencies/module_deps_cache_reuse.swift
@@ -2,10 +2,10 @@
 // RUN: mkdir -p %t/clang-module-cache
 
 // Run the scanner once, emitting the serialized scanner cache
-// RUN: %target-swift-frontend -scan-dependencies -Rdependency-scan-cache -serialize-dependency-scan-cache -dependency-scan-cache-path %t/cache.moddepcache -module-cache-path %t/clang-module-cache %s -o %t/deps_initial.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -import-objc-header %S/Inputs/CHeaders/Bridging.h -swift-version 4 2>&1 | %FileCheck %s -check-prefix CHECK-REMARK-SAVE
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -Rdependency-scan-cache -serialize-dependency-scan-cache -dependency-scan-cache-path %t/cache.moddepcache -module-cache-path %t/clang-module-cache %s -o %t/deps_initial.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -import-objc-header %S/Inputs/CHeaders/Bridging.h -swift-version 4 2>&1 | %FileCheck %s -check-prefix CHECK-REMARK-SAVE
 
 // Run the scanner again, but now re-using previously-serialized cache
-// RUN: %target-swift-frontend -scan-dependencies -Rdependency-scan-cache -load-dependency-scan-cache -dependency-scan-cache-path %t/cache.moddepcache -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -import-objc-header %S/Inputs/CHeaders/Bridging.h -swift-version 4 2>&1 | %FileCheck %s -check-prefix CHECK-REMARK-LOAD
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -Rdependency-scan-cache -load-dependency-scan-cache -dependency-scan-cache-path %t/cache.moddepcache -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -import-objc-header %S/Inputs/CHeaders/Bridging.h -swift-version 4 2>&1 | %FileCheck %s -check-prefix CHECK-REMARK-LOAD
 
 // Check the contents of the JSON output
 // RUN: %validate-json %t/deps.json &>/dev/null
diff --git a/test/ScanDependencies/module_deps_cross_import_overlay.swift b/test/ScanDependencies/module_deps_cross_import_overlay.swift
index b7a047a3b7461..c5a663ca9a551 100644
--- a/test/ScanDependencies/module_deps_cross_import_overlay.swift
+++ b/test/ScanDependencies/module_deps_cross_import_overlay.swift
@@ -1,11 +1,11 @@
 // RUN: %empty-directory(%t)
 // RUN: mkdir -p %t/clang-module-cache
-// RUN: %target-swift-frontend -scan-dependencies -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -I %S/Inputs/CHeaders/ExtraCModules -emit-dependencies -emit-dependencies-path %t/deps.d -import-objc-header %S/Inputs/CHeaders/Bridging.h -swift-version 4 -module-name CrossImportTestModule
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -I %S/Inputs/CHeaders/ExtraCModules -emit-dependencies -emit-dependencies-path %t/deps.d -import-objc-header %S/Inputs/CHeaders/Bridging.h -swift-version 4 -module-name CrossImportTestModule
 // Check the contents of the JSON output
 // RUN: %validate-json %t/deps.json | %FileCheck %s
 
 // Ensure that round-trip serialization does not affect result
-// RUN: %target-swift-frontend -scan-dependencies -test-dependency-scan-cache-serialization -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -I %S/Inputs/CHeaders/ExtraCModules -emit-dependencies -emit-dependencies-path %t/deps.d -import-objc-header %S/Inputs/CHeaders/Bridging.h -swift-version 4 -module-name CrossImportTestModule
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -test-dependency-scan-cache-serialization -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -I %S/Inputs/CHeaders/ExtraCModules -emit-dependencies -emit-dependencies-path %t/deps.d -import-objc-header %S/Inputs/CHeaders/Bridging.h -swift-version 4 -module-name CrossImportTestModule
 // RUN: %validate-json %t/deps.json | %FileCheck %s
 
 // REQUIRES: executable_test
diff --git a/test/ScanDependencies/module_deps_different_paths_no_reuse.swift b/test/ScanDependencies/module_deps_different_paths_no_reuse.swift
index 9844160fe9e61..0afa3bab97918 100644
--- a/test/ScanDependencies/module_deps_different_paths_no_reuse.swift
+++ b/test/ScanDependencies/module_deps_different_paths_no_reuse.swift
@@ -4,12 +4,12 @@
 // This test ensures that subsequent invocations of the dependency scanner that re-use previous cache state do not re-use cache entries that contain modules found outside of the current scanner invocation's search paths.
 
 // Run the scanner once, emitting the serialized scanner cache, with one set of search paths
-// RUN: %target-swift-frontend -scan-dependencies -serialize-dependency-scan-cache -dependency-scan-cache-path %t/cache.moddepcache -module-cache-path %t/clang-module-cache %s -o %t/deps_initial.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -import-objc-header %S/Inputs/CHeaders/Bridging.h -swift-version 4
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -serialize-dependency-scan-cache -dependency-scan-cache-path %t/cache.moddepcache -module-cache-path %t/clang-module-cache %s -o %t/deps_initial.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -import-objc-header %S/Inputs/CHeaders/Bridging.h -swift-version 4
 // RUN: %validate-json %t/deps_initial.json &>/dev/null
 // RUN: %FileCheck -input-file %t/deps_initial.json %s -check-prefix CHECK-INITIAL-SCAN
 
 // Run the scanner again, but now re-using previously-serialized cache and using a different search path for Swift modules
-// RUN: %target-swift-frontend -scan-dependencies -load-dependency-scan-cache -dependency-scan-cache-path %t/cache.moddepcache -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/SwiftDifferent -import-objc-header %S/Inputs/CHeaders/Bridging.h -swift-version 4
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -load-dependency-scan-cache -dependency-scan-cache-path %t/cache.moddepcache -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/SwiftDifferent -import-objc-header %S/Inputs/CHeaders/Bridging.h -swift-version 4
 // RUN: %validate-json %t/deps.json &>/dev/null
 // RUN: %FileCheck -input-file %t/deps.json %s -check-prefix CHECK-DIFFERENT
 
diff --git a/test/ScanDependencies/module_deps_external.swift b/test/ScanDependencies/module_deps_external.swift
index 515d7a33edcb7..37a61b6b349e4 100644
--- a/test/ScanDependencies/module_deps_external.swift
+++ b/test/ScanDependencies/module_deps_external.swift
@@ -10,7 +10,7 @@
 // RUN: echo "\"isFramework\": false" >> %/t/inputs/map.json
 // RUN: echo "}]" >> %/t/inputs/map.json
 
-// RUN: %target-swift-frontend -scan-dependencies -module-cache-path %t/clang-module-cache %s -placeholder-dependency-module-map-file %t/inputs/map.json -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -emit-dependencies -emit-dependencies-path %t/deps.d -import-objc-header %S/Inputs/CHeaders/Bridging.h -swift-version 4
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -module-cache-path %t/clang-module-cache %s -placeholder-dependency-module-map-file %t/inputs/map.json -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -emit-dependencies -emit-dependencies-path %t/deps.d -import-objc-header %S/Inputs/CHeaders/Bridging.h -swift-version 4
 
 // Check the contents of the JSON output
 // RUN: %validate-json %t/deps.json | %FileCheck %s
@@ -28,7 +28,7 @@
 // RUN: %target-run %t/main %t/deps.json
 
 // Ensure that round-trip serialization does not affect result
-// RUN: %target-swift-frontend -scan-dependencies -test-dependency-scan-cache-serialization -module-cache-path %t/clang-module-cache %s -placeholder-dependency-module-map-file %t/inputs/map.json -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -import-objc-header %S/Inputs/CHeaders/Bridging.h -swift-version 4
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -test-dependency-scan-cache-serialization -module-cache-path %t/clang-module-cache %s -placeholder-dependency-module-map-file %t/inputs/map.json -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -import-objc-header %S/Inputs/CHeaders/Bridging.h -swift-version 4
 // RUN: %validate-json %t/deps.json | %FileCheck %s
 
 // REQUIRES: executable_test
diff --git a/test/ScanDependencies/module_framework.swift b/test/ScanDependencies/module_framework.swift
index 296ac57759690..2789c058fe21d 100644
--- a/test/ScanDependencies/module_framework.swift
+++ b/test/ScanDependencies/module_framework.swift
@@ -1,11 +1,11 @@
 // REQUIRES: OS=macosx
 // RUN: %empty-directory(%t)
-// RUN: %target-swift-frontend -scan-dependencies %s -o %t/deps.json -emit-dependencies -emit-dependencies-path %t/deps.d -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import -F %S/Inputs/Frameworks
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface %s -o %t/deps.json -emit-dependencies -emit-dependencies-path %t/deps.d -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import -F %S/Inputs/Frameworks
 // Check the contents of the JSON output
 // RUN: %validate-json %t/deps.json | %FileCheck %s
 
 // Ensure that round-trip serialization does not affect result
-// RUN: %target-swift-frontend -scan-dependencies -test-dependency-scan-cache-serialization %s -o %t/deps.json -emit-dependencies -emit-dependencies-path %t/deps.d -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import -F %S/Inputs/Frameworks
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -test-dependency-scan-cache-serialization %s -o %t/deps.json -emit-dependencies -emit-dependencies-path %t/deps.d -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import -F %S/Inputs/Frameworks
 // RUN: %validate-json %t/deps.json | %FileCheck %s
 
 import ScannerTestKit
diff --git a/test/ScanDependencies/module_load_mode.swift b/test/ScanDependencies/module_load_mode.swift
new file mode 100644
index 0000000000000..29ab5996dc185
--- /dev/null
+++ b/test/ScanDependencies/module_load_mode.swift
@@ -0,0 +1,21 @@
+// RUN: %empty-directory(%t)
+// RUN: split-file %s %t
+
+// RUN: %target-swift-frontend -emit-module %t/Foo.swift -emit-module-path %t/Foo.swiftmodule/%target-swiftmodule-name -module-name Foo -emit-module-interface-path %t/Foo.swiftmodule/%target-swiftinterface-name -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import -parse-stdlib
+
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode only-serialized \
+// RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import -parse-stdlib \
+// RUN:   %t/main.swift -I %t -o - | %FileCheck %s --check-prefix=SERIALIZED
+
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode only-interface \
+// RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import -parse-stdlib \
+// RUN:   %t/main.swift -I %t -o - | %FileCheck %s --check-prefix=INTERFACE
+
+// SERIALIZED: "swiftPrebuiltExternal": "Foo"
+// INTERFACE: "swift": "Foo"
+
+//--- main.swift
+import Foo
+
+//--- Foo.swift
+public func foo() {}
diff --git a/test/ScanDependencies/no_cross_import_module_for_self.swift b/test/ScanDependencies/no_cross_import_module_for_self.swift
index 4d34d97e1692c..042baf7ace9f6 100644
--- a/test/ScanDependencies/no_cross_import_module_for_self.swift
+++ b/test/ScanDependencies/no_cross_import_module_for_self.swift
@@ -1,6 +1,6 @@
 // RUN: %empty-directory(%t)
 // RUN: mkdir -p %t/clang-module-cache
-// RUN: %target-swift-frontend -scan-dependencies -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/CHeaders/ExtraCModules -I %S/Inputs/Swift -emit-dependencies -emit-dependencies-path %t/deps.d -swift-version 4 -module-name _cross_import_E
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/CHeaders/ExtraCModules -I %S/Inputs/Swift -emit-dependencies -emit-dependencies-path %t/deps.d -swift-version 4 -module-name _cross_import_E
 // Check the contents of the JSON output
 // RUN: %validate-json %t/deps.json | %FileCheck %s
 
diff --git a/test/ScanDependencies/no_main_module_cross_import.swift b/test/ScanDependencies/no_main_module_cross_import.swift
index a111f9737fe0c..4aa299a9d4ee5 100644
--- a/test/ScanDependencies/no_main_module_cross_import.swift
+++ b/test/ScanDependencies/no_main_module_cross_import.swift
@@ -1,6 +1,6 @@
 // RUN: %empty-directory(%t)
 // RUN: mkdir -p %t/clang-module-cache
-// RUN: %target-swift-frontend -scan-dependencies -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/CHeaders/ExtraCModules -I %S/Inputs/Swift -emit-dependencies -emit-dependencies-path %t/deps.d -swift-version 4 -module-name SubE
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/CHeaders/ExtraCModules -I %S/Inputs/Swift -emit-dependencies -emit-dependencies-path %t/deps.d -swift-version 4 -module-name SubE
 // Check the contents of the JSON output
 // RUN: %validate-json %t/deps.json | %FileCheck %s
 
diff --git a/test/ScanDependencies/package_interface.swift b/test/ScanDependencies/package_interface.swift
index 4688fa3575698..0d0f0b079cb8c 100644
--- a/test/ScanDependencies/package_interface.swift
+++ b/test/ScanDependencies/package_interface.swift
@@ -9,21 +9,21 @@
 // RUN:   -emit-private-module-interface-path %t/Bar.private.swiftinterface \
 // RUN:   -emit-package-module-interface-path %t/Bar.package.swiftinterface
 
-// RUN: %target-swift-frontend -scan-dependencies -o %t/deps.json -I %t -experimental-package-interface-load \
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -o %t/deps.json -I %t -experimental-package-interface-load \
 // RUN:   %t/Client.swift -module-name Client -package-name barpkg -swift-version 5
 // RUN: %FileCheck %s --input-file=%t/deps.json --check-prefix CHECK --check-prefix CHECK-PACKAGE
 
 /// When package name doesn't match or not used, it should find private interface.
-// RUN: %target-swift-frontend -scan-dependencies -o %t/deps2.json -I %t -experimental-package-interface-load \
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -o %t/deps2.json -I %t -experimental-package-interface-load \
 // RUN:   %t/Client.swift -module-name Client -package-name foopkg -swift-version 5
 // RUN: %FileCheck %s --input-file=%t/deps2.json --check-prefix CHECK --check-prefix CHECK-PRIVATE
 
-// RUN: %target-swift-frontend -scan-dependencies -o %t/deps3.json -I %t -experimental-package-interface-load \
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -o %t/deps3.json -I %t -experimental-package-interface-load \
 // RUN:   %t/Client.swift -module-name Client -swift-version 5
 // RUN: %FileCheck %s --input-file=%t/deps3.json --check-prefix CHECK --check-prefix CHECK-PRIVATE
 
 /// If -experimental-package-interface-load is not used but in the same package, it should find the binary module
-// RUN: %target-swift-frontend -scan-dependencies -I %t \
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -I %t \
 // RUN:   %t/Client.swift -module-name Client -package-name barpkg -swift-version 5 | \
 // RUN:   %FileCheck %s --check-prefix CHECK-BINARY
 
diff --git a/test/ScanDependencies/preserve_used_vfs.swift b/test/ScanDependencies/preserve_used_vfs.swift
index 6efbe236b2a9f..d7348931bf4ec 100644
--- a/test/ScanDependencies/preserve_used_vfs.swift
+++ b/test/ScanDependencies/preserve_used_vfs.swift
@@ -6,7 +6,7 @@
 
 // RUN: sed -e "s|OUT_DIR|%t/redirects|g"  -e "s|IN_DIR|%S/Inputs/CHeaders|g" %t/overlay_template.yaml > %t/overlay.yaml
 
-// RUN: %target-swift-frontend -scan-dependencies -module-cache-path %t/module-cache %t/test.swift -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import -Xcc -ivfsoverlay -Xcc %t/overlay.yaml
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -module-cache-path %t/module-cache %t/test.swift -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import -Xcc -ivfsoverlay -Xcc %t/overlay.yaml
 // RUN: %validate-json %t/deps.json | %FileCheck %s
 
 //--- redirects/RedirectedF.h
diff --git a/test/ScanDependencies/private_interface_candidate_module.swift b/test/ScanDependencies/private_interface_candidate_module.swift
index bf6752ee14555..41d9dd9013718 100644
--- a/test/ScanDependencies/private_interface_candidate_module.swift
+++ b/test/ScanDependencies/private_interface_candidate_module.swift
@@ -15,7 +15,7 @@
 // RUN: %target-swift-frontend -emit-module -emit-module-path %t/Frameworks/E.framework/Modules/E.swiftmodule/%module-target-triple.swiftmodule -module-cache-path %t.module-cache %t/foo.swift -module-name E
 
 // Run the scan
-// RUN: %target-swift-frontend -scan-dependencies %s -o %t/deps.json -F %t/Frameworks/ -sdk %t
+// RUN: %target-swift-frontend -scan-dependencies -no-scanner-module-validation %s -o %t/deps.json -F %t/Frameworks/ -sdk %t
 // RUN: %validate-json %t/deps.json | %FileCheck %s
 
 import E
diff --git a/test/ScanDependencies/separate_bridging_header_deps.swift b/test/ScanDependencies/separate_bridging_header_deps.swift
index 69e5de969112b..f9c9ed02bc758 100644
--- a/test/ScanDependencies/separate_bridging_header_deps.swift
+++ b/test/ScanDependencies/separate_bridging_header_deps.swift
@@ -1,7 +1,7 @@
 // RUN: %empty-directory(%t)
 // RUN: mkdir -p %t/clang-module-cache
 
-// RUN: %target-swift-frontend -scan-dependencies -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -import-objc-header %S/Inputs/CHeaders/Bridging.h -swift-version 4
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -import-objc-header %S/Inputs/CHeaders/Bridging.h -swift-version 5
 // RUN: %validate-json %t/deps.json | %FileCheck %s
 
 import E
diff --git a/test/ScanDependencies/testable-dependencies.swift b/test/ScanDependencies/testable-dependencies.swift
new file mode 100644
index 0000000000000..87c5166ae0282
--- /dev/null
+++ b/test/ScanDependencies/testable-dependencies.swift
@@ -0,0 +1,80 @@
+// RUN: %empty-directory(%t)
+// RUN: split-file %s %t
+
+// RUN: %target-swift-frontend -emit-module -module-name B -o %t/internal/B.swiftmodule -swift-version 5 \
+// RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import -parse-stdlib \
+// RUN:   -emit-module-interface-path %t/internal/B.swiftinterface -enable-library-evolution -I %t \
+// RUN:   %t/B.swift
+
+// RUN: %target-swift-frontend -emit-module -module-name A -o %t/testable/A.swiftmodule -swift-version 5 \
+// RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import -parse-stdlib \
+// RUN:   -emit-module-interface-path %t/testable/A.swiftinterface -enable-library-evolution -I %t/internal -enable-testing \
+// RUN:   %t/A.swift
+
+// RUN: %target-swift-frontend -emit-module -module-name A -o %t/regular/A.swiftmodule -swift-version 5 \
+// RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import -parse-stdlib \
+// RUN:   -emit-module-interface-path %t/regular/A.swiftinterface -enable-library-evolution -I %t/internal \
+// RUN:   %t/A.swift
+
+/// Import testable build, should use binary but no extra dependencies.
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-serialized -module-name Test %t/main.swift \
+// RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import -parse-stdlib \
+// RUN:   -o %t/deps1.json -I %t/testable -swift-version 5 -Rmodule-loading
+// RUN: %{python} %S/../CAS/Inputs/SwiftDepsExtractor.py %t/deps1.json Test directDependencies | %FileCheck %s --check-prefix TEST1
+// TEST1:  "swiftPrebuiltExternal": "A"
+// RUN: %{python} %S/../CAS/Inputs/SwiftDepsExtractor.py %t/deps1.json A directDependencies | %FileCheck %s --check-prefix EMPTY --allow-empty
+// EMPTY-NOT: B
+
+/// Import regular build, should use binary.
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-serialized -module-name Test %t/main.swift \
+// RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import -parse-stdlib \
+// RUN:   -o %t/deps2.json -I %t/regular -swift-version 5 -Rmodule-loading
+// RUN: %{python} %S/../CAS/Inputs/SwiftDepsExtractor.py %t/deps2.json Test directDependencies | %FileCheck %s --check-prefix TEST2
+// TEST2:  "swiftPrebuiltExternal": "A"
+// RUN: %{python} %S/../CAS/Inputs/SwiftDepsExtractor.py %t/deps2.json swiftPrebuiltExternal:A directDependencies | %FileCheck %s --check-prefix EMPTY --allow-empty
+
+/// Testable import testable build, should use binary, even interface is preferred.
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -module-name Test %t/testable.swift \
+// RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import -parse-stdlib -enable-testing \
+// RUN:   -o %t/deps3.json -I %t/testable -I %t/internal -swift-version 5 -Rmodule-loading
+// RUN: %{python} %S/../CAS/Inputs/SwiftDepsExtractor.py %t/deps3.json Test directDependencies | %FileCheck %s --check-prefix TEST3
+// TEST3:  "swiftPrebuiltExternal": "A"
+// RUN: %{python} %S/../CAS/Inputs/SwiftDepsExtractor.py %t/deps3.json swiftPrebuiltExternal:A directDependencies | %FileCheck %s --check-prefix TEST3-A
+// TEST3-A:  "swift": "B"
+
+/// Testable import non-testable build without enable testing.
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -module-name Test %t/testable.swift \
+// RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import -parse-stdlib \
+// RUN:   -o %t/deps4.json -I %t/regular -swift-version 5
+// RUN: %{python} %S/../CAS/Inputs/SwiftDepsExtractor.py %t/deps4.json Test directDependencies | %FileCheck %s --check-prefix TEST4
+// TEST4:  "swiftPrebuiltExternal": "A"
+// RUN: %{python} %S/../CAS/Inputs/SwiftDepsExtractor.py %t/deps4.json swiftPrebuiltExternal:A directDependencies | %FileCheck %s --check-prefix EMPTY --allow-empty
+
+/// Testable import non-testable build enable testing, still succeed since swift-frontend can provide a better diagnostics when the module is actually imported.
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -module-name Test %t/testable.swift \
+// RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import -parse-stdlib -enable-testing \
+// RUN:   -o %t/deps5.json -I %t/regular -swift-version 5 -Rmodule-loading
+
+/// Regular import a testable module with no interface, don't load optional dependencies.
+// RUN: rm %t/testable/A.swiftinterface
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -module-name Test %t/main.swift \
+// RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import -parse-stdlib -enable-testing \
+// RUN:   -o %t/deps6.json -I %t/testable -swift-version 5 -Rmodule-loading
+// RUN: %{python} %S/../CAS/Inputs/SwiftDepsExtractor.py %t/deps6.json Test directDependencies | %FileCheck %s --check-prefix TEST6
+// TEST6:  "swiftPrebuiltExternal": "A"
+// RUN: %{python} %S/../CAS/Inputs/SwiftDepsExtractor.py %t/deps6.json swiftPrebuiltExternal:A directDependencies | %FileCheck %s --check-prefix EMPTY --allow-empty
+
+
+//--- main.swift
+import A
+
+//--- testable.swift
+@testable import A
+
+//--- A.swift
+internal import B
+@_spi(Testing) public func a() {}
+
+//--- B.swift
+public func b() {}
+
diff --git a/test/ScanDependencies/testable-import.swift b/test/ScanDependencies/testable-import.swift
index d2323cf9e3bf8..d6e57bd9c66c7 100644
--- a/test/ScanDependencies/testable-import.swift
+++ b/test/ScanDependencies/testable-import.swift
@@ -16,14 +16,14 @@
 // RUN:   -emit-module-interface-path %t/A.swiftinterface -enable-library-evolution -I %t -enable-testing \
 // RUN:   %t/A.swift
 
-// RUN: %target-swift-frontend -scan-dependencies -module-name Test %t/test1.swift \
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -module-name Test %t/test1.swift \
 // RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import -parse-stdlib -enable-testing \
 // RUN:   -o %t/deps1.json -I %t -swift-version 5
 // RUN: %{python} %S/../CAS/Inputs/SwiftDepsExtractor.py %t/deps1.json Test directDependencies | %FileCheck %s --check-prefix TEST1
 // TEST1-DAG: "swiftPrebuiltExternal": "B"
 // TEST1-DAG: "swift": "C"
 
-// RUN: %target-swift-frontend -scan-dependencies -module-name Test %t/test2.swift \
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -module-name Test %t/test2.swift \
 // RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import -parse-stdlib -enable-testing \
 // RUN:   -o %t/deps2.json -I %t -swift-version 5
 // RUN: %{python} %S/../CAS/Inputs/SwiftDepsExtractor.py %t/deps2.json Test directDependencies | %FileCheck %s --check-prefix TEST2
@@ -36,7 +36,7 @@
 // TEST2-A-DAG: "swift": "C"
 
 /// An indirect @testable import is still interface deps.
-// RUN: %target-swift-frontend -scan-dependencies -module-name Test %t/test3.swift \
+// RUN: %target-swift-frontend -scan-dependencies -module-load-mode prefer-interface -module-name Test %t/test3.swift \
 // RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import -parse-stdlib -enable-testing \
 // RUN:   -o %t/deps3.json -I %t -swift-version 5
 // RUN: %{python} %S/../CAS/Inputs/SwiftDepsExtractor.py %t/deps3.json Test directDependencies | %FileCheck %s --check-prefix TEST3