[Dependency Scanning] Add option to specify a separate Clang Dependency scanner module cache.

Clang dependency scanning produces scanner PCMs which we may want to live in a different filesystem location than the main build module cache.

Resolves rdar://113222853

Author: artemcm

Sources/SwiftDriver/ExplicitModuleBuilds/ModuleDependencyScanning.swift

@@ -121,6 +121,7 @@ public extension Driver {
     }
 
     try commandLine.appendLast(.clangIncludeTree, from: &parsedOptions)
+    try commandLine.appendLast(.clangScannerModuleCachePath, from: &parsedOptions)
 
     // Pass on the input files
     commandLine.append(contentsOf: inputFiles.filter { $0.type == .swift }.map { .path($0.file) })

Sources/SwiftOptions/Options.swift

@@ -75,6 +75,7 @@ extension Option {
   public static let clangHeaderExposeModule: Option = Option("-clang-header-expose-module", .separate, attributes: [.helpHidden, .frontend, .noDriver], metaVar: "<imported-module-name>=<generated-header-name>", helpText: "Allow the compiler to assume that APIs from the specified module are exposed to C/C++/Objective-C in another generated header, so that APIs in the current module that depend on declarations from the specified module can be exposed in the generated header.")
   public static let clangIncludeTreeRoot: Option = Option("-clang-include-tree-root", .separate, attributes: [.helpHidden, .frontend, .noDriver], metaVar: "<cas-id>", helpText: "Clang Include Tree CASID")
   public static let clangIncludeTree: Option = Option("-clang-include-tree", .flag, attributes: [.helpHidden, .frontend, .noDriver], helpText: "Use clang include tree")
+  public static let clangScannerModuleCachePath: Option = Option("-clang-scanner-module-cache-path", .separate, attributes: [.frontend, .doesNotAffectIncrementalBuild, .argumentIsPath], helpText: "Specifies the Clang dependency scanner module cache path")
   public static let clangTarget: Option = Option("-clang-target", .separate, attributes: [.frontend], helpText: "Separately set the target we should use for internal Clang instance")
   public static let codeCompleteCallPatternHeuristics: Option = Option("-code-complete-call-pattern-heuristics", .flag, attributes: [.helpHidden, .frontend, .noDriver], helpText: "Use heuristics to guess whether we want call pattern completions")
   public static let codeCompleteInitsInPostfixExpr: Option = Option("-code-complete-inits-in-postfix-expr", .flag, attributes: [.helpHidden, .frontend, .noDriver], helpText: "Include initializers when completing a postfix expression")
@@ -869,6 +870,7 @@ extension Option {
       Option.clangHeaderExposeModule,
       Option.clangIncludeTreeRoot,
       Option.clangIncludeTree,
+      Option.clangScannerModuleCachePath,
       Option.clangTarget,
       Option.codeCompleteCallPatternHeuristics,
       Option.codeCompleteInitsInPostfixExpr,

Tests/SwiftDriverTests/ExplicitModuleBuildTests.swift

@@ -1365,6 +1365,28 @@ final class ExplicitModuleBuildTests: XCTestCase {
     }
   }
 
+  /// Test that the scanner invocation does not rely in response files
+  func testDependencyScanningSeparateClangScanCache() throws {
+    try withTemporaryDirectory { path in
+      let scannerCachePath: AbsolutePath = path.appending(component: "ClangScannerCache")
+      let moduleCachePath: AbsolutePath = path.appending(component: "ModuleCache")
+      let main = path.appending(component: "testDependencyScanningSeparateClangScanCache.swift")
+      let sdkArgumentsForTesting = (try? Driver.sdkArgumentsForTesting()) ?? []
+      var driver = try Driver(args: ["swiftc",
+                                     "-explicit-module-build",
+                                     "-clang-scanner-module-cache-path",
+                                     scannerCachePath.nativePathString(escaped: true),
+                                     "-module-cache-path",
+                                     moduleCachePath.nativePathString(escaped: true),
+                                     "-working-directory", path.nativePathString(escaped: true),
+                                     main.nativePathString(escaped: true)] + sdkArgumentsForTesting,
+                              env: ProcessEnv.vars)
+      let scannerJob = try driver.dependencyScanningJob()
+      XCTAssertTrue(scannerJob.commandLine.contains(subsequence: [.flag("-clang-scanner-module-cache-path"),
+                                                                  .path(.absolute(scannerCachePath))]))
+    }
+  }
+
   func testDependencyScanningFailure() throws {
     let (stdlibPath, shimsPath, toolchain, _) = try getDriverArtifactsForScanning()