[Explicit Module Builds] Add support for '-clang-target-variant' flag

Adds equivalent functionality to that specified by '-clang-target' but for the zippered library variant on Darwin platforms.

Author: artemcm

Sources/SwiftDriver/Toolchains/DarwinToolchain.swift

@@ -453,6 +453,23 @@ public final class DarwinToolchain: Toolchain {
 
       commandLine.appendFlag(.clangTarget)
       commandLine.appendFlag(clangTargetTriple)
+
+      // Repeat the above for the '-target-variant' flag
+      if driver.parsedOptions.contains(.targetVariant),
+         driver.isFrontendArgSupported(.clangTargetVariant),
+         let targetVariantTripleStr = frontendTargetInfo.targetVariant?.triple {
+        let clangTargetVariantTriple: String
+        if let explicitClangTargetVariantArg = driver.parsedOptions.getLastArgument(.clangTargetVariant)?.asSingle {
+          clangTargetVariantTriple = explicitClangTargetVariantArg
+        } else {
+          let currentVariantTriple = targetVariantTripleStr
+          let sdkVersionedOSSString = currentVariantTriple.osNameUnversioned + sdkInfo.sdkVersion(for: currentVariantTriple).sdkVersionString
+          clangTargetVariantTriple = currentVariantTriple.triple.replacingOccurrences(of: currentVariantTriple.osName, with: sdkVersionedOSSString)
+        }
+
+        commandLine.appendFlag(.clangTargetVariant)
+        commandLine.appendFlag(clangTargetVariantTriple)
+      }
     }
 
     if driver.isFrontendArgSupported(.externalPluginPath) {

Sources/SwiftOptions/Options.swift

@@ -86,6 +86,7 @@ extension Option {
   public static let clangIncludeTreeFilelist: Option = Option("-clang-include-tree-filelist", .separate, attributes: [.helpHidden, .frontend, .noDriver], metaVar: "<cas-id>", helpText: "Clang Include Tree FileList CASID")
   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 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 clangTargetVariant: Option = Option("-clang-target-variant", .separate, attributes: [.frontend, .synthesizeInterface], helpText: "Separately set the target we should use for internal Clang instance for the 'zippered' code for macCatalyst")
   public static let clangTarget: Option = Option("-clang-target", .separate, attributes: [.frontend, .synthesizeInterface], 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")
@@ -1029,6 +1030,7 @@ extension Option {
       Option.clangIncludeTreeFilelist,
       Option.clangIncludeTreeRoot,
       Option.clangScannerModuleCachePath,
+      Option.clangTargetVariant,
       Option.clangTarget,
       Option.codeCompleteCallPatternHeuristics,
       Option.codeCompleteInitsInPostfixExpr,

Tests/SwiftDriverTests/SwiftDriverTests.swift

@@ -4346,6 +4346,32 @@ final class SwiftDriverTests: XCTestCase {
         job.commandLine.contains(.flag("-clang-target"))
       })
     }
+
+    // Check -clang-target-variant is handled correctly with the MacCatalyst remap.
+    try withTemporaryDirectory { path in
+      let main = path.appending(component: "Foo.swift")
+      try localFileSystem.writeFileContents(main, bytes:
+        """
+        import Swift
+        """
+      )
+      var driver = try Driver(args: ["swiftc", "-explicit-module-build",
+                                     "-target", "arm64e-apple-ios13.0-macabi",
+                                     "-target-variant", "arm64e-apple-macos10.0",
+                                     "-sdk", sdkRoot.pathString,
+                                     main.pathString])
+      guard driver.isFrontendArgSupported(.clangTarget) else {
+        throw XCTSkip("Skipping: compiler does not support '-clang-target'")
+      }
+      guard driver.isFrontendArgSupported(.clangTargetVariant) else {
+        throw XCTSkip("Skipping: compiler does not support '-clang-target-variant'")
+      }
+      let plannedJobs = try driver.planBuild()
+      XCTAssertTrue(plannedJobs.contains { job in
+        job.commandLine.contains(subsequence: [.flag("-clang-target"), .flag("arm64e-apple-ios13.3-macabi")]) &&
+        job.commandLine.contains(subsequence: [.flag("-clang-target-variant"), .flag("arm64e-apple-macos10.15")])
+      })
+    }
     #endif
   }