[WIP] Invoke the Swift frontend to prescan for dependencies.

Sources/SwiftDriver/Dependency Scanning/ModuleDependencyGraph.swift

@@ -0,0 +1,135 @@
+//===--------------- ModuleDependencyGraph.swift --------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2019 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+import Foundation
+
+enum ModuleDependencyId: Hashable {
+  case swift(String)
+  case clang(String)
+
+  var moduleName: String {
+    switch self {
+      case .swift(let name): return name
+      case .clang(let name): return name
+    }
+  }
+}
+
+extension ModuleDependencyId: Codable {
+  enum CodingKeys: CodingKey {
+    case swift
+    case clang
+  }
+
+  init(from decoder: Decoder) throws {
+    let container = try decoder.container(keyedBy: CodingKeys.self)
+    do {
+      let moduleName =  try container.decode(String.self, forKey: .swift)
+      self = .swift(moduleName)
+    } catch {
+      let moduleName =  try container.decode(String.self, forKey: .clang)
+      self = .clang(moduleName)
+    }
+  }
+
+  func encode(to encoder: Encoder) throws {
+    var container = encoder.container(keyedBy: CodingKeys.self)
+    switch self {
+      case .swift(let moduleName):
+        try container.encode(moduleName, forKey: .swift)
+      case .clang(let moduleName):
+        try container.encode(moduleName, forKey: .clang)
+    }
+  }
+}
+
+/// Details specific to Swift modules.
+struct SwiftModuleDetails: Codable {
+  /// The module interface from which this module was built, if any.
+  var moduleInterfacePath: String?
+
+  /// The bridging header, if any.
+  var bridgingHeaderPath: String?
+
+  /// The source files referenced by the bridging header.
+  var bridgingSourceFiles: [String] = []
+}
+
+/// Details specific to Clang modules.
+struct ClangModuleDetails: Codable {
+  /// The path to the module map used to build this module.
+  var moduleMapPath: String
+}
+
+struct ModuleDependencies: Codable {
+  /// The path for the module.
+  var modulePath: String
+
+  /// The source files used to build this module.
+  var sourceFiles: [String] = []
+
+  /// The set of direct module dependencies of this module.
+  var directDependencies: [ModuleDependencyId] = []
+
+  /// Specific details of a particular kind of module.
+  var details: Details
+
+  /// Specific details of a particular kind of module.
+  enum Details {
+    /// Swift modules may be built from a module interface, and may have
+    /// a bridging header.
+    case swift(SwiftModuleDetails)
+
+    /// Clang modules are built from a module map file.
+    case clang(ClangModuleDetails)
+  }
+}
+
+extension ModuleDependencies.Details: Codable {
+  enum CodingKeys: CodingKey {
+    case swift
+    case clang
+  }
+
+  init(from decoder: Decoder) throws {
+    let container = try decoder.container(keyedBy: CodingKeys.self)
+    do {
+      let details = try container.decode(SwiftModuleDetails.self, forKey: .swift)
+      self = .swift(details)
+    } catch {
+      let details = try container.decode(ClangModuleDetails.self, forKey: .clang)
+      self = .clang(details)
+    }
+  }
+
+  func encode(to encoder: Encoder) throws {
+    var container = encoder.container(keyedBy: CodingKeys.self)
+    switch self {
+      case .swift(let details):
+        try container.encode(details, forKey: .swift)
+      case .clang(let details):
+        try container.encode(details, forKey: .clang)
+    }
+  }
+}
+
+/// Describes the complete set of dependencies for a Swift module, including
+/// all of the Swift and C modules and source files it depends on.
+struct ModuleDependencyGraph: Codable {
+  /// The name of the main module.
+  var mainModuleName: String
+
+  /// The complete set of modules discovered
+  var modules: [ModuleDependencyId: ModuleDependencies] = [:]
+
+  /// Information about the main module.
+  var mainModule: ModuleDependencies { modules[.swift(mainModuleName)]! }
+}

Sources/SwiftDriver/Driver/Driver.swift

@@ -156,6 +156,11 @@ 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 moduleDependencyGraph: ModuleDependencyGraph? = nil
+
   /// Handler for emitting diagnostics to stderr.
   public static let stderrDiagnosticsHandler: DiagnosticsEngine.DiagnosticsHandler = { diagnostic in
     let stream = stderrStream

Sources/SwiftDriver/Driver/ModuleDependencyScanning.swift

@@ -0,0 +1,81 @@
+//===--------------- ModuleDependencyScanning.swift -----------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2019 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+import Foundation
+import TSCBasic
+
+extension Driver {
+  /// Produce a Swift job to to compute the full module dependency graph
+  /// in advance, allowing the driver to schedule explicit module builds.
+  mutating func moduleDependencyGraphJob() throws -> Job {
+    var commandLine: [Job.ArgTemplate] = swiftCompilerPrefixArgs.map { Job.ArgTemplate.flag($0) }
+    commandLine.appendFlag("-frontend")
+    commandLine.appendFlag("-emit-imported-modules")
+
+    if parsedOptions.hasArgument(.parseStdlib) {
+      commandLine.appendFlag(.disableObjcAttrRequiresFoundationModule)
+    }
+
+    try addCommonFrontendOptions(commandLine: &commandLine)
+    // FIXME: MSVC runtime flags
+
+    commandLine.append(contentsOf: inputFiles.map { Job.ArgTemplate.path($0.file)})
+    return Job(
+      kind: .moduleDependencyGraph,
+      tool: swiftCompiler,
+      commandLine: commandLine,
+      displayInputs: inputFiles,
+      inputs: inputFiles,
+      outputs: []
+    )
+  }
+
+  private class ModuleDependencyGraphExecutionDelegate : JobExecutorDelegate {
+    var moduleDependencyGraph: ModuleDependencyGraph? = nil
+
+    func jobStarted(job: Job, arguments: [String], pid: Int) {
+    }
+
+    func jobFinished(job: Job, result: ProcessResult, pid: Int) {
+      switch result.exitStatus {
+      case .terminated(code: 0):
+        guard let outputData = try? Data(result.utf8Output().utf8) else {
+          return
+        }
+
+        let decoder = JSONDecoder()
+        moduleDependencyGraph = try? decoder.decode(
+            ModuleDependencyGraph.self, from: outputData)
+
+      default:
+        break;
+      }
+    }
+  }
+
+  /// Precompute the dependencies for a given Swift compilation, producing a
+  /// complete dependency graph including all Swift and C module files and
+  /// source files.
+  mutating func computeModuleDependencyGraph() throws
+      -> ModuleDependencyGraph? {
+    let job = try moduleDependencyGraphJob()
+    let resolver = try ArgsResolver()
+    let executorDelegate = ModuleDependencyGraphExecutionDelegate()
+    let jobExecutor = JobExecutor(
+        jobs: [job], resolver: resolver,
+        executorDelegate: executorDelegate
+    )
+    try jobExecutor.execute(env: [:])
+
+    // FIXME: Handle errors properly
+    return executorDelegate.moduleDependencyGraph
+  }
+}

Sources/SwiftDriver/Jobs/Job.swift

@@ -22,6 +22,7 @@ public struct Job: Codable, Equatable {
     case emitModule = "emit-module"
     case interpret
     case repl
+    case moduleDependencyGraph = "emit-imported-modules"
   }
 
   public enum ArgTemplate: Equatable {

Sources/SwiftDriver/Jobs/Planning.swift

@@ -28,6 +28,15 @@ extension Driver {
   private mutating func planStandardCompile() throws -> [Job] {
     var jobs = [Job]()
 
+    // If we've been asked to prebuild module dependencies, prescan the source
+    // files to produce a module dependency graph.
+    if parsedOptions.contains(.driverPrebuildModuleDependencies) {
+      moduleDependencyGraph = try computeModuleDependencyGraph()
+      if let graph = moduleDependencyGraph {
+        print(graph)
+      }
+    }
+
     // Keep track of the various outputs we care about from the jobs we build.
     var linkerInputs: [TypedVirtualPath] = []
     var moduleInputs: [TypedVirtualPath] = []

Sources/SwiftDriver/Options/ExtraOptions.swift

@@ -12,9 +12,12 @@
 extension Option {
   public static let driverPrintGraphviz: Option = Option("-driver-print-graphviz", .flag, attributes: [.helpHidden, .doesNotAffectIncrementalBuild], helpText: "Write the job graph as a graphviz file", group: .internalDebug)
 
+  public static let driverPrebuildModuleDependencies: Option = Option("-driver-prebuild-module-dependencies", .flag, attributes: [.helpHidden], helpText: "Prebuild module dependencies to make them explicit")
+
   public static var extraOptions: [Option] {
     return [
-      Option.driverPrintGraphviz
+      Option.driverPrintGraphviz,
+      Option.driverPrebuildModuleDependencies
     ]
   }
 }