[BridgingHeader] Provide a deterministic unique pch file path

Teach swift driver to use a deterministic path for compiled PCH output.
Also when dependency scanner is updated to return a module scanning or
PCH hash from the scanning result, it will add that to the code path to
have an unique PCH file path for the specific compilation.

(cherry picked from commit bb3eed3)

Author: cachemeifyoucan

Sources/SwiftDriver/Driver/Driver.swift

@@ -336,7 +336,14 @@ public struct Driver {
   let importedObjCHeader: VirtualPath.Handle?
 
   /// The path to the pch for the imported Objective-C header.
-  let bridgingPrecompiledHeader: VirtualPath.Handle?
+  lazy var bridgingPrecompiledHeader: VirtualPath.Handle? = {
+    let contextHash = try? explicitDependencyBuildPlanner?.getMainModuleContextHash()
+    return Self.computeBridgingPrecompiledHeader(&parsedOptions,
+                                                 compilerMode: compilerMode,
+                                                 importedObjCHeader: importedObjCHeader,
+                                                 outputFileMap: outputFileMap,
+                                                 contextHash: contextHash)
+  }()
 
   /// Path to the dependencies file.
   let dependenciesFilePath: VirtualPath.Handle?
@@ -801,10 +808,6 @@ public struct Driver {
       recordedInputModificationDates: recordedInputModificationDates)
 
     self.importedObjCHeader = try Self.computeImportedObjCHeader(&parsedOptions, compilerMode: compilerMode, diagnosticEngine: diagnosticEngine)
-    self.bridgingPrecompiledHeader = try Self.computeBridgingPrecompiledHeader(&parsedOptions,
-                                                                               compilerMode: compilerMode,
-                                                                               importedObjCHeader: importedObjCHeader,
-                                                                               outputFileMap: outputFileMap)
 
     self.supportedFrontendFlags =
       try Self.computeSupportedCompilerArgs(of: self.toolchain,
@@ -829,7 +832,7 @@ public struct Driver {
         diagnosticsEngine.emit(.warning("-cache-compile-job cannot be used without explicit module build, turn off caching"),
                                location: nil)
         self.enableCaching = false
-      } else if importedObjCHeader != nil && bridgingPrecompiledHeader == nil {
+      } else if importedObjCHeader != nil, !parsedOptions.hasFlag(positive: .enableBridgingPch, negative: .disableBridgingPch, default: true) {
         diagnosticsEngine.emit(.warning("-cache-compile-job cannot be used with -disable-bridging-pch, turn off caching"),
                                location: nil)
         self.enableCaching = false
@@ -1779,7 +1782,7 @@ extension Driver {
   /// The swift-driver doesn't have actions, so the logic here takes the jobs and tries
   /// to mimic the actions that would be created by the C++ driver and
   /// prints them in *hopefully* the same order.
-  private func printActions(_ jobs: [Job]) {
+  private mutating func printActions(_ jobs: [Job]) {
     defer {
       stdoutStream.flush()
     }
@@ -2872,23 +2875,29 @@ extension Driver {
   static func computeBridgingPrecompiledHeader(_ parsedOptions: inout ParsedOptions,
                                                compilerMode: CompilerMode,
                                                importedObjCHeader: VirtualPath.Handle?,
-                                               outputFileMap: OutputFileMap?) throws -> VirtualPath.Handle? {
+                                               outputFileMap: OutputFileMap?,
+                                               contextHash: String?) -> VirtualPath.Handle? {
     guard compilerMode.supportsBridgingPCH,
       let input = importedObjCHeader,
       parsedOptions.hasFlag(positive: .enableBridgingPch, negative: .disableBridgingPch, default: true) else {
         return nil
     }
 
-    if let outputPath = try outputFileMap?.existingOutput(inputFile: input, outputType: .pch) {
+    if let outputPath = try? outputFileMap?.existingOutput(inputFile: input, outputType: .pch) {
       return outputPath
     }
 
-    let inputFile = VirtualPath.lookup(input)
-    let pchFileName = inputFile.basenameWithoutExt.appendingFileTypeExtension(.pch)
+    let pchFile : String
+    let baseName = VirtualPath.lookup(input).basenameWithoutExt
+    if let hash = contextHash {
+      pchFile = baseName + "-" + hash + ".pch"
+    } else {
+      pchFile = baseName.appendingFileTypeExtension(.pch)
+    }
     if let outputDirectory = parsedOptions.getLastArgument(.pchOutputDir)?.asSingle {
-      return try VirtualPath(path: outputDirectory).appending(component: pchFileName).intern()
+      return try? VirtualPath(path: outputDirectory).appending(component: pchFile).intern()
     } else {
-      return try VirtualPath.createUniqueTemporaryFile(RelativePath(validating: pchFileName)).intern()
+      return try? VirtualPath.temporary(RelativePath(validating: pchFile)).intern()
     }
   }
 }

Sources/SwiftDriver/ExplicitModuleBuilds/ExplicitDependencyBuildPlanner.swift

@@ -425,6 +425,13 @@ public typealias ExternalTargetModuleDetailsMap = [ModuleDependencyId: ExternalT
     commandLine.append(contentsOf: mainModuleDependenciesArgs.commandLine)
   }
 
+  /// Get the context hash for the main module.
+  public func getMainModuleContextHash() throws -> String? {
+    let mainModuleId: ModuleDependencyId = .swift(dependencyGraph.mainModuleName)
+    let mainModuleDetails = try dependencyGraph.swiftModuleDetails(of: mainModuleId)
+    return mainModuleDetails.contextHash
+  }
+
   /// Resolve all module dependencies of the main module and add them to the lists of
   /// inputs and command line flags.
   public mutating func resolveBridgingHeaderDependencies(inputs: inout [TypedVirtualPath],

Tests/SwiftDriverTests/CachingBuildTests.swift

@@ -324,7 +324,7 @@ final class CachingBuildTests: XCTestCase {
               let baseName = "testCachingBuildJobs"
               XCTAssertTrue(matchTemporary(outputFilePath, basename: baseName, fileExtension: "o") ||
                             matchTemporary(outputFilePath, basename: baseName, fileExtension: "autolink") ||
-                            matchTemporary(outputFilePath, basename: "Bridging-", fileExtension: "pch"))
+                            matchTemporary(outputFilePath, basename: "Bridging", fileExtension: "pch"))
             default:
               XCTFail("Unexpected module dependency build job output: \(outputFilePath)")
           }

Tests/SwiftDriverTests/ExplicitModuleBuildTests.swift

@@ -388,7 +388,7 @@ final class ExplicitModuleBuildTests: XCTestCase {
               let baseName = "testExplicitModuleBuildJobs"
               XCTAssertTrue(matchTemporary(outputFilePath, basename: baseName, fileExtension: "o") ||
                             matchTemporary(outputFilePath, basename: baseName, fileExtension: "autolink") ||
-                            matchTemporary(outputFilePath, basename: "Bridging-", fileExtension: "pch"))
+                            matchTemporary(outputFilePath, basename: "Bridging", fileExtension: "pch"))
             default:
               XCTFail("Unexpected module dependency build job output: \(outputFilePath)")
           }