Propagate Explicit Module Build command arguments to compile jobs.

Sources/SwiftDriver/Dependency Scanning/ModuleDependencyBuildGeneration.swift

@@ -16,8 +16,9 @@ import Foundation
 extension Driver {
   /// For the current moduleDependencyGraph, plan the order and generate jobs
   /// for explicitly building all dependency modules.
-  mutating func planExplicitModuleDependenciesCompile(dependencyGraph: InterModuleDependencyGraph)
-  throws -> [Job] {
+  mutating func planExplicitModuleDependenciesCompile(
+    dependencyGraph: InterModuleDependencyGraph
+  ) throws -> [Job] {
     var jobs: [Job] = []
     for (id, moduleInfo) in dependencyGraph.modules {
       // The generation of the main module file will be handled elsewhere in the driver.
@@ -26,23 +27,27 @@ extension Driver {
       }
       switch id {
         case .swift(let moduleName):
-          let swiftModuleBuildJob = try genSwiftModuleDependencyBuildJob(moduleInfo: moduleInfo,
-                                                                         moduleName: moduleName)
+          let swiftModuleBuildJob =
+            try genSwiftModuleDependencyBuildJob(moduleInfo: moduleInfo,
+                                                 moduleName: moduleName,
+                                                 dependencyGraph: dependencyGraph)
           jobs.append(swiftModuleBuildJob)
         case .clang(let moduleName):
-          let clangModuleBuildJob = try genClangModuleDependencyBuildJob(moduleInfo: moduleInfo,
-                                                                         moduleName: moduleName)
+          let clangModuleBuildJob =
+            try genClangModuleDependencyBuildJob(moduleInfo: moduleInfo,
+                                                 moduleName: moduleName,
+                                                 dependencyGraph: dependencyGraph)
           jobs.append(clangModuleBuildJob)
-
       }
     }
     return jobs
   }
 
   /// For a given swift module dependency, generate a build job
   mutating private func genSwiftModuleDependencyBuildJob(moduleInfo: ModuleInfo,
-                                                         moduleName: String) throws -> Job {
-    // FIXIT: Needs more error handling
+                                                         moduleName: String,
+                                                         dependencyGraph: InterModuleDependencyGraph
+  ) throws -> Job {
     guard case .swift(let swiftModuleDetails) = moduleInfo.details else {
       throw Error.malformedModuleDependency(moduleName, "no `details` object")
     }
@@ -52,7 +57,18 @@ extension Driver {
       TypedVirtualPath(file: try VirtualPath(path: moduleInfo.modulePath), type: .swiftModule)
     ]
     var commandLine: [Job.ArgTemplate] = swiftCompilerPrefixArgs.map { Job.ArgTemplate.flag($0) }
-    commandLine.appendFlag("-frontend")
+    // First, take the command line options provided in the dependency information
+    swiftModuleDetails.commandLine?.forEach { commandLine.appendFlags($0) }
+
+    if (swiftModuleDetails.commandLine == nil ||
+          !swiftModuleDetails.commandLine!.contains("-frontend")) {
+      commandLine.appendFlag("-frontend")
+    }
+
+    try addModuleDependencies(moduleInfo: moduleInfo,
+                              dependencyGraph: dependencyGraph,
+                              inputs: &inputs,
+                              commandLine: &commandLine)
 
     // Build the .swiftinterfaces file using a list of command line options specified in the
     // `details` field.
@@ -62,7 +78,6 @@ extension Driver {
     inputs.append(TypedVirtualPath(file: try VirtualPath(path: moduleInterfacePath),
                                    type: .swiftInterface))
     try addCommonModuleOptions(commandLine: &commandLine, outputs: &outputs)
-    swiftModuleDetails.commandLine?.forEach { commandLine.appendFlag($0) }
 
     return Job(
       moduleName: moduleName,
@@ -76,7 +91,9 @@ extension Driver {
 
   /// For a given clang module dependency, generate a build job
   mutating private func genClangModuleDependencyBuildJob(moduleInfo: ModuleInfo,
-                                                         moduleName: String) throws -> Job {
+                                                         moduleName: String,
+                                                         dependencyGraph: InterModuleDependencyGraph
+  ) throws -> Job {
     // For clang modules, the Fast Dependency Scanner emits a list of source
     // files (with a .modulemap among them), and a list of compile command
     // options.
@@ -89,15 +106,27 @@ extension Driver {
       TypedVirtualPath(file: try VirtualPath(path: moduleInfo.modulePath), type: .pcm)
     ]
     var commandLine: [Job.ArgTemplate] = swiftCompilerPrefixArgs.map { Job.ArgTemplate.flag($0) }
-    commandLine.appendFlag("-frontend")
+
+    // First, take the command line options provided in the dependency information
+    clangModuleDetails.commandLine?.forEach { commandLine.appendFlags($0) }
+
+    if (clangModuleDetails.commandLine == nil ||
+          !clangModuleDetails.commandLine!.contains("-frontend")) {
+      commandLine.appendFlag("-frontend")
+    }
     commandLine.appendFlags("-emit-pcm", "-module-name", moduleName)
 
+    try addModuleDependencies(moduleInfo: moduleInfo,
+                              dependencyGraph: dependencyGraph,
+                              inputs: &inputs,
+                              commandLine: &commandLine)
+
     // The only required input is the .modulemap for this module.
-    commandLine.append(Job.ArgTemplate.path(try VirtualPath(path: clangModuleDetails.moduleMapPath)))
+    commandLine.append(Job.ArgTemplate.path(
+                        try VirtualPath(path: clangModuleDetails.moduleMapPath)))
     inputs.append(TypedVirtualPath(file: try VirtualPath(path: clangModuleDetails.moduleMapPath),
                                    type: .clangModuleMap))
     try addCommonModuleOptions(commandLine: &commandLine, outputs: &outputs)
-    clangModuleDetails.commandLine?.forEach { commandLine.appendFlags("-Xcc", $0) }
 
     return Job(
       moduleName: moduleName,
@@ -108,4 +137,24 @@ extension Driver {
       outputs: outputs
     )
   }
+
+
+  /// For the specified module, update its command line flags and inputs
+  /// to use explicitly-built module dependencies.
+  private func addModuleDependencies(moduleInfo: ModuleInfo,
+                                     dependencyGraph: InterModuleDependencyGraph,
+                                     inputs: inout [TypedVirtualPath],
+                                     commandLine: inout [Job.ArgTemplate]) throws {
+    // Prohibit the frontend from implicitly building textual modules into binary modules.
+    commandLine.appendFlags("-disable-implicit-swift-modules", "-Xcc", "-Xclang", "-Xcc",
+                            "-fno-implicit-modules")
+    for moduleId in moduleInfo.directDependencies {
+      guard let dependencyInfo = dependencyGraph.modules[moduleId] else {
+        throw Error.missingModuleDependency(moduleId.moduleName)
+      }
+      try addModuleAsExplicitDependency(moduleInfo: dependencyInfo,
+                                        dependencyGraph: dependencyGraph,
+                                        commandLine: &commandLine, inputs: &inputs)
+    }
+  }
 }

Sources/SwiftDriver/Driver/Driver.swift

@@ -50,7 +50,10 @@ public struct Driver {
     case subcommandPassedToDriver
     case integratedReplRemoved
     case conflictingOptions(Option, Option)
+    // Explicit Module Build Failures
     case malformedModuleDependency(String, String)
+    case missingModuleDependency(String)
+    case dependencyScanningFailure(Int, String)
 
     public var description: String {
       switch self {
@@ -69,8 +72,13 @@ public struct Driver {
         return "Compiler-internal integrated REPL has been removed; use the LLDB-enhanced REPL instead."
       case .conflictingOptions(let one, let two):
         return "conflicting options '\(one.spelling)' and '\(two.spelling)'"
+      // Explicit Module Build Failures
       case .malformedModuleDependency(let moduleName, let errorDescription):
         return "Malformed Module Dependency: \(moduleName), \(errorDescription)"
+      case .missingModuleDependency(let moduleName):
+        return "Missing Module Dependency Info: \(moduleName)"
+      case .dependencyScanningFailure(let code, let error):
+        return "Module Dependency Scanner returned with non-zero exit status: \(code), \(error)"
       }
     }
   }
@@ -200,6 +208,11 @@ public struct Driver {
   /// This will force the driver to first emit the module and then run compile jobs.
   public var forceEmitModuleInSingleInvocation: Bool = false
 
+  /// The module dependency graph, which is populated during the planning phase
+  /// only when all modules will be prebuilt and treated as explicit by the
+  /// various compilation jobs.
+  var interModuleDependencyGraph: InterModuleDependencyGraph? = nil
+
   /// Handler for emitting diagnostics to stderr.
   public static let stderrDiagnosticsHandler: DiagnosticsEngine.DiagnosticsHandler = { diagnostic in
     let stream = stderrStream

Sources/SwiftDriver/Driver/ModuleDependencyScanning.swift

@@ -23,6 +23,7 @@ extension Driver {
     let resolver = try ArgsResolver()
     let compilerPath = VirtualPath.absolute(try toolchain.getToolPath(.swiftCompiler))
     let tool = try resolver.resolve(.path(compilerPath))
+    var inputs: [TypedVirtualPath] = []
 
     // Aggregate the fast dependency scanner arguments
     var commandLine: [Job.ArgTemplate] = swiftCompilerPrefixArgs.map { Job.ArgTemplate.flag($0) }
@@ -31,7 +32,9 @@ extension Driver {
     if parsedOptions.hasArgument(.parseStdlib) {
        commandLine.appendFlag(.disableObjcAttrRequiresFoundationModule)
     }
-    try addCommonFrontendOptions(commandLine: &commandLine)
+    try addCommonFrontendOptions(commandLine: &commandLine, inputs: &inputs,
+                                 bridgingHeaderHandling: .precompiled,
+                                 moduleDependencyGraphUse: .dependencyScan)
     // FIXME: MSVC runtime flags
 
     // Pass on the input files
@@ -41,6 +44,17 @@ extension Driver {
     let arguments = [tool] + (try commandLine.map { try resolver.resolve($0) })
     let scanProcess = try Process.launchProcess(arguments: arguments, env: env)
     let result = try scanProcess.waitUntilExit()
+    // Error on dependency scanning failure
+    if (result.exitStatus != .terminated(code: 0)) {
+      var returnCode = 0
+      switch result.exitStatus {
+        case .terminated(let code):
+          returnCode = Int(code)
+        case .signalled(let signal):
+          returnCode = Int(signal)
+      }
+      throw Error.dependencyScanningFailure(returnCode, try result.utf8stderrOutput())
+    }
     guard let outputData = try? Data(result.utf8Output().utf8) else {
       return nil
     }

Sources/SwiftDriver/Jobs/CompileJob.swift

@@ -152,7 +152,7 @@ extension Driver {
       commandLine.appendFlag(.disableObjcAttrRequiresFoundationModule)
     }
 
-    try addCommonFrontendOptions(commandLine: &commandLine)
+    try addCommonFrontendOptions(commandLine: &commandLine, inputs: &inputs)
     // FIXME: MSVC runtime flags
 
     if parsedOptions.hasArgument(.parseAsLibrary, .emitLibrary) {

Sources/SwiftDriver/Jobs/EmitModuleJob.swift

@@ -60,7 +60,7 @@ extension Driver {
       inputs.append(input)
     }
 
-    try addCommonFrontendOptions(commandLine: &commandLine)
+    try addCommonFrontendOptions(commandLine: &commandLine, inputs: &inputs)
     // FIXME: Add MSVC runtime library flags
 
     try addCommonModuleOptions(commandLine: &commandLine, outputs: &outputs)

Sources/SwiftDriver/Jobs/FrontendJobHelpers.swift

@@ -35,10 +35,21 @@ extension Driver {
     /// Use the precompiled bridging header.
     case precompiled
   }
+  /// Whether the driver has already constructed a module dependency graph or is in the process
+  /// of doing so
+  enum ModuleDependencyGraphUse {
+    /// Even though the driver may be in ExplicitModuleBuild mode, the dependency graph has not yet
+    /// been constructed, omit processing module dependencies
+    case dependencyScan
+    /// If the driver is in Explicit Module Build mode, the dependency graph has been computed
+    case computed
+  }
   /// Add frontend options that are common to different frontend invocations.
   mutating func addCommonFrontendOptions(
     commandLine: inout [Job.ArgTemplate],
-    bridgingHeaderHandling: BridgingHeaderHandling = .precompiled
+    inputs: inout [TypedVirtualPath],
+    bridgingHeaderHandling: BridgingHeaderHandling = .precompiled,
+    moduleDependencyGraphUse: ModuleDependencyGraphUse = .computed
   ) throws {
     // Only pass -target to the REPL or immediate modes if it was explicitly
     // specified on the command line.
@@ -54,6 +65,18 @@ extension Driver {
       }
     }
 
+    // If in ExplicitModuleBuild mode and the dependency graph has been computed, add module
+    // dependencies.
+    // May also be used for generation of the dependency graph itself in ExplicitModuleBuild mode.
+    if (parsedOptions.contains(.driverExplicitModuleBuild) &&
+          moduleDependencyGraphUse == .computed) {
+      guard let dependencyGraph = interModuleDependencyGraph else {
+        fatalError("Attempting to add Explicit Module job dependencies, but the Inter Module Dependency Graph does not exist.")
+      }
+      try addExplicitModuleBuildArguments(dependencyGraph: dependencyGraph,
+                                          commandLine: &commandLine, inputs: &inputs)
+    }
+
     if let variant = parsedOptions.getLastArgument(.targetVariant)?.asSingle {
       commandLine.appendFlag(.targetVariant)
       commandLine.appendFlag(Triple(variant, normalizing: true).triple)
@@ -304,4 +327,62 @@ extension Driver {
 
     return outputs
   }
+
+  /// Adds the specified module as an explicit module dependency to given
+  /// inputs and command line arguments of a compile job.
+  /// Also adds transitive dependencies that arise from dependencies of this module.
+  func addModuleAsExplicitDependency(moduleInfo: ModuleInfo,
+                                     dependencyGraph: InterModuleDependencyGraph,
+                                     commandLine: inout [Job.ArgTemplate],
+                                     inputs: inout [TypedVirtualPath]) throws {
+    switch moduleInfo.details {
+      case .swift:
+        let swiftModulePath = TypedVirtualPath(file: try VirtualPath(path: moduleInfo.modulePath),
+                                               type: .swiftModule)
+        commandLine.appendFlags("-swift-module-file")
+        commandLine.appendPath(swiftModulePath.file)
+        inputs.append(swiftModulePath)
+      case .clang(let clangDependencyDetails):
+        let clangModulePath = TypedVirtualPath(file: try VirtualPath(path: moduleInfo.modulePath),
+                                               type: .pcm)
+        let clangModuleMapPath = TypedVirtualPath(file: try VirtualPath(path: clangDependencyDetails.moduleMapPath),
+                                                  type: .pcm)
+        commandLine.appendFlags("-Xcc", "-Xclang", "-Xcc",
+                                "-fmodule-map-file=\(clangModuleMapPath.file.description)")
+        commandLine.appendFlags("-Xcc", "-Xclang", "-Xcc",
+                                "-fmodule-file=\(clangModulePath.file.description)")
+        inputs.append(clangModulePath)
+        inputs.append(clangModuleMapPath)
+    }
+    // Add transitive dependencies to the command line as well
+    for transitiveDependencyId in moduleInfo.directDependencies {
+      guard let transitiveDependencyInfo = dependencyGraph.modules[transitiveDependencyId] else {
+        throw Error.missingModuleDependency(transitiveDependencyId.moduleName)
+      }
+      try addModuleAsExplicitDependency(moduleInfo: transitiveDependencyInfo,
+                                        dependencyGraph: dependencyGraph,
+                                        commandLine: &commandLine,
+                                        inputs: &inputs)
+    }
+  }
+
+  /// Adds all dependecies required for an explicit module build
+  /// to inputs and comman line arguments of a compile job.
+  func addExplicitModuleBuildArguments(dependencyGraph: InterModuleDependencyGraph,
+                                       commandLine: inout [Job.ArgTemplate],
+                                       inputs: inout [TypedVirtualPath]) throws {
+    // Prohibit the frontend from implicitly building textual modules into binary modules.
+    commandLine.appendFlags("-disable-implicit-swift-modules", "-Xcc", "-Xclang", "-Xcc",
+                            "-fno-implicit-modules")
+
+    // Provide the frontend with a list of explicitly pre-built modules.
+    for (moduleId, moduleInfo) in dependencyGraph.modules {
+      // Skip the main output module as it is not its own dependency
+      guard moduleId.moduleName != dependencyGraph.mainModuleName else {
+        continue
+      }
+      try addModuleAsExplicitDependency(moduleInfo: moduleInfo, dependencyGraph: dependencyGraph,
+                                        commandLine: &commandLine, inputs: &inputs)
+    }
+  }
 }

Sources/SwiftDriver/Jobs/GeneratePCHJob.swift

@@ -23,7 +23,7 @@ extension Driver {
     commandLine.appendFlag("-frontend")
 
     try addCommonFrontendOptions(
-      commandLine: &commandLine, bridgingHeaderHandling: .parsed)
+      commandLine: &commandLine, inputs: &inputs, bridgingHeaderHandling: .parsed)
 
     try commandLine.appendLast(.indexStorePath, from: &parsedOptions)
 

Sources/SwiftDriver/Jobs/GeneratePCMJob.swift

@@ -48,7 +48,7 @@ extension Driver {
     commandLine.appendPath(output.file)
 
     try addCommonFrontendOptions(
-      commandLine: &commandLine, bridgingHeaderHandling: .ignored)
+      commandLine: &commandLine, inputs: &inputs, bridgingHeaderHandling: .ignored)
 
     try commandLine.appendLast(.indexStorePath, from: &parsedOptions)
 

Sources/SwiftDriver/Jobs/InterpretJob.swift

@@ -27,7 +27,7 @@ extension Driver {
       commandLine.appendFlag(.disableObjcAttrRequiresFoundationModule)
     }
 
-    try addCommonFrontendOptions(commandLine: &commandLine)
+    try addCommonFrontendOptions(commandLine: &commandLine, inputs: &inputs)
     // FIXME: MSVC runtime flags
 
     try commandLine.appendLast(.parseSil, from: &parsedOptions)

Sources/SwiftDriver/Jobs/MergeModuleJob.swift

@@ -41,7 +41,7 @@ extension Driver {
     commandLine.appendFlag(.disableDiagnosticPasses)
     commandLine.appendFlag(.disableSilPerfOptzns)
 
-    try addCommonFrontendOptions(commandLine: &commandLine)
+    try addCommonFrontendOptions(commandLine: &commandLine, inputs: &inputs)
     // FIXME: Add MSVC runtime library flags
 
     try addCommonModuleOptions(commandLine: &commandLine, outputs: &outputs)