[6.2 🍒][Dependency Scanning] On failure to locate a module, attempt to diagnose if binary dependencies contain search paths with this module.

include/swift/AST/DiagnosticGroups.def

@@ -50,6 +50,7 @@ GROUP(ExistentialAny, "existential-any")
 GROUP(ExistentialMemberAccess, "existential-member-access-limitations")
 GROUP(IsolatedConformances, "isolated-conformances")
 GROUP(MemberImportVisibility, "member-import-visibility")
+GROUP(MissingModuleOnKnownPaths, "missing-module-on-known-paths")
 GROUP(MultipleInheritance, "multiple-inheritance")
 GROUP(MutableGlobalVariable, "mutable-global-variable")
 GROUP(NominalTypes, "nominal-types")

include/swift/AST/DiagnosticsSema.def

@@ -2332,12 +2332,18 @@ ERROR(alignment_not_power_of_two,none,
 
 // Dependency Scanning
 ERROR(dependency_scan_module_not_found, none, "Unable to find module dependency: '%0'", (StringRef))
+GROUPED_ERROR(dependency_scan_module_not_found_on_specified_search_paths, MissingModuleOnKnownPaths, none,
+              "Compilation search paths unable to resolve module dependency: '%0'", (StringRef))
 NOTE(unresolved_import_location,none,
      "also imported here", ())
 NOTE(dependency_as_imported_by_main_module,none,
      "a dependency of main module '%0'", (StringRef))
 NOTE(dependency_as_imported_by, none,
      "a dependency of %select{Swift|Clang}2 module '%0': '%1'", (StringRef, StringRef, bool))
+NOTE(inherited_search_path_resolves_module,none,
+     "'%0' can be found using a search path that was specified when building module '%1' ('%2'). "
+     "This search path was not explicitly specified on the current compilation.", (StringRef, StringRef, StringRef))
+
 ERROR(clang_dependency_scan_error, none, "Clang dependency scanner failure: %0", (StringRef))
 ERROR(clang_header_dependency_scan_error, none, "Bridging header dependency scan failure: %0", (StringRef))
 

include/swift/AST/ModuleDependencies.h

@@ -22,6 +22,7 @@
 #include "swift/AST/LinkLibrary.h"
 #include "swift/Basic/CXXStdlibKind.h"
 #include "swift/Basic/LLVM.h"
+#include "swift/Serialization/Validation.h"
 #include "clang/CAS/CASOptions.h"
 #include "clang/Tooling/DependencyScanning/DependencyScanningService.h"
 #include "clang/Tooling/DependencyScanning/DependencyScanningTool.h"
@@ -406,15 +407,18 @@ class SwiftBinaryModuleDependencyStorage
       StringRef sourceInfoPath,
       ArrayRef<ScannerImportStatementInfo> moduleImports,
       ArrayRef<ScannerImportStatementInfo> optionalModuleImports,
-      ArrayRef<LinkLibrary> linkLibraries, StringRef headerImport,
-      StringRef definingModuleInterface, bool isFramework, bool isStatic,
-      StringRef moduleCacheKey, StringRef userModuleVersion)
+      ArrayRef<LinkLibrary> linkLibraries,
+      ArrayRef<serialization::SearchPath> serializedSearchPaths,
+      StringRef headerImport, StringRef definingModuleInterface,
+      bool isFramework, bool isStatic, StringRef moduleCacheKey,
+      StringRef userModuleVersion)
       : ModuleDependencyInfoStorageBase(ModuleDependencyKind::SwiftBinary,
                                         moduleImports, optionalModuleImports,
                                         linkLibraries, moduleCacheKey),
         compiledModulePath(compiledModulePath), moduleDocPath(moduleDocPath),
         sourceInfoPath(sourceInfoPath), headerImport(headerImport),
         definingModuleInterfacePath(definingModuleInterface),
+        serializedSearchPaths(serializedSearchPaths),
         isFramework(isFramework), isStatic(isStatic),
         userModuleVersion(userModuleVersion) {}
 
@@ -441,6 +445,9 @@ class SwiftBinaryModuleDependencyStorage
   /// Source files on which the header inputs depend.
   std::vector<std::string> headerSourceFiles;
 
+  /// Search paths this module was built with which got serialized
+  std::vector<serialization::SearchPath> serializedSearchPaths;
+
   /// (Clang) modules on which the header inputs depend.
   std::vector<ModuleDependencyID> headerModuleDependencies;
 
@@ -613,15 +620,17 @@ class ModuleDependencyInfo {
       StringRef sourceInfoPath,
       ArrayRef<ScannerImportStatementInfo> moduleImports,
       ArrayRef<ScannerImportStatementInfo> optionalModuleImports,
-      ArrayRef<LinkLibrary> linkLibraries, StringRef headerImport,
-      StringRef definingModuleInterface, bool isFramework,
-      bool isStatic, StringRef moduleCacheKey, StringRef userModuleVer) {
+      ArrayRef<LinkLibrary> linkLibraries,
+      ArrayRef<serialization::SearchPath> serializedSearchPaths,
+      StringRef headerImport, StringRef definingModuleInterface,
+      bool isFramework, bool isStatic, StringRef moduleCacheKey,
+      StringRef userModuleVer) {
     return ModuleDependencyInfo(
         std::make_unique<SwiftBinaryModuleDependencyStorage>(
             compiledModulePath, moduleDocPath, sourceInfoPath, moduleImports,
-            optionalModuleImports, linkLibraries, headerImport,
-            definingModuleInterface,isFramework, isStatic, moduleCacheKey,
-            userModuleVer));
+            optionalModuleImports, linkLibraries, serializedSearchPaths,
+            headerImport, definingModuleInterface,isFramework, isStatic,
+            moduleCacheKey, userModuleVer));
   }
 
   /// Describe the main Swift module.

include/swift/DependencyScan/ModuleDependencyScanner.h

@@ -190,8 +190,26 @@ class ModuleDependencyScanner {
   template <typename Function, typename... Args>
   auto withDependencyScanningWorker(Function &&F, Args &&...ArgList);
 
+  /// Use the scanner's ASTContext to construct an `Identifier`
+  /// for a given module name.
   Identifier getModuleImportIdentifier(StringRef moduleName);
 
+  /// Diagnose scanner failure and attempt to reconstruct the dependency
+  /// path from the main module to the missing dependency.
+  void diagnoseScannerFailure(const ScannerImportStatementInfo &moduleImport,
+                              const ModuleDependenciesCache &cache,
+                              std::optional<ModuleDependencyID> dependencyOf);
+
+  /// Assuming the \c `moduleImport` failed to resolve,
+  /// iterate over all binary Swift module dependencies with serialized
+  /// search paths and attempt to diagnose if the failed-to-resolve module
+  /// can be found on any of them. Returns the path containing
+  /// the module, if one is found.
+  std::optional<std::pair<ModuleDependencyID, std::string>>
+  attemptToFindResolvingSerializedSearchPath(
+      const ScannerImportStatementInfo &moduleImport,
+      const ModuleDependenciesCache &cache, const SourceLoc &importLoc);
+
 private:
   const CompilerInvocation &ScanCompilerInvocation;
   ASTContext &ScanASTContext;

include/swift/DependencyScan/SerializedModuleDependencyCacheFormat.h

@@ -41,7 +41,7 @@ using llvm::BCVBR;
 const unsigned char MODULE_DEPENDENCY_CACHE_FORMAT_SIGNATURE[] = {'I', 'M', 'D','C'};
 const unsigned MODULE_DEPENDENCY_CACHE_FORMAT_VERSION_MAJOR = 9;
 /// Increment this on every change.
-const unsigned MODULE_DEPENDENCY_CACHE_FORMAT_VERSION_MINOR = 2;
+const unsigned MODULE_DEPENDENCY_CACHE_FORMAT_VERSION_MINOR = 3;
 
 /// Various identifiers in this format will rely on having their strings mapped
 /// using this ID.
@@ -78,6 +78,7 @@ using ModuleCacheKeyIDField = IdentifierIDField;
 using ImportArrayIDField = IdentifierIDField;
 using LinkLibrariesArrayIDField = IdentifierIDField;
 using MacroDependenciesArrayIDField = IdentifierIDField;
+using SearchPathArrayIDField = IdentifierIDField;
 using FlagIDArrayIDField = IdentifierIDField;
 using DependencyIDArrayIDField = IdentifierIDField;
 using SourceLocationIDArrayIDField = IdentifierIDField;
@@ -101,6 +102,8 @@ enum {
   LINK_LIBRARY_ARRAY_NODE,
   MACRO_DEPENDENCY_NODE,
   MACRO_DEPENDENCY_ARRAY_NODE,
+  SEARCH_PATH_NODE,
+  SEARCH_PATH_ARRAY_NODE,
   IMPORT_STATEMENT_NODE,
   IMPORT_STATEMENT_ARRAY_NODE,
   OPTIONAL_IMPORT_STATEMENT_ARRAY_NODE,
@@ -169,6 +172,17 @@ using MacroDependencyLayout =
 using MacroDependencyArrayLayout =
     BCRecordLayout<MACRO_DEPENDENCY_ARRAY_NODE, IdentifierIDArryField>;
 
+// A record for a serialized search pathof a given dependency
+// node (Swift binary module dependency only).
+using SearchPathLayout =
+    BCRecordLayout<SEARCH_PATH_NODE,             // ID
+                   IdentifierIDField,            // path
+                   IsFrameworkField,             // isFramework
+                   IsSystemField                 // isSystem
+                   >;
+using SearchPathArrayLayout =
+    BCRecordLayout<SEARCH_PATH_ARRAY_NODE, IdentifierIDArryField>;
+
 // A record capturing information about a given 'import' statement
 // captured in a dependency node, including its source location.
 using ImportStatementLayout =
@@ -248,6 +262,7 @@ using SwiftBinaryModuleDetailsLayout =
                    FileIDField,                      // definingInterfacePath
                    IdentifierIDField,                // headerModuleDependencies
                    FileIDArrayIDField,               // headerSourceFiles
+                   SearchPathArrayIDField,           // serializedSearchPaths
                    IsFrameworkField,                 // isFramework
                    IsStaticField,                    // isStatic
                    IdentifierIDField,                // moduleCacheKey