Enable -clang-target on Darwin platforms set to the SDK version by-default

Author: artemcm

Sources/SwiftDriver/Jobs/FrontendJobHelpers.swift

@@ -72,17 +72,6 @@ extension Driver {
       break
     }
 
-    // Pass down -clang-target.
-    // If not specified otherwise, we should use the same triple as -target
-    // TODO: enable -clang-target for implicit module build as well.
-    if !parsedOptions.hasArgument(.disableClangTarget) &&
-        isFrontendArgSupported(.clangTarget) &&
-        parsedOptions.contains(.driverExplicitModuleBuild) {
-      let clangTriple = parsedOptions.getLastArgument(.clangTarget)?.asSingle ?? targetTriple.triple
-      commandLine.appendFlag(.clangTarget)
-      commandLine.appendFlag(clangTriple)
-    }
-
     // 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.
@@ -324,7 +313,7 @@ extension Driver {
     try toolchain.addPlatformSpecificCommonFrontendOptions(commandLine: &commandLine,
                                                            inputs: &inputs,
                                                            frontendTargetInfo: frontendTargetInfo,
-                                                           driver: self)
+                                                           driver: &self)
   }
 
   mutating func addFrontendSupplementaryOutputArguments(commandLine: inout [Job.ArgTemplate],

Sources/SwiftDriver/Toolchains/DarwinToolchain.swift

@@ -371,7 +371,7 @@ public final class DarwinToolchain: Toolchain {
     commandLine: inout [Job.ArgTemplate],
     inputs: inout [TypedVirtualPath],
     frontendTargetInfo: FrontendTargetInfo,
-    driver: Driver
+    driver: inout Driver
   ) throws {
     guard let sdkPath = frontendTargetInfo.sdkPath?.path,
           let sdkInfo = getTargetSDKInfo(sdkPath: sdkPath) else { return }
@@ -401,6 +401,29 @@ public final class DarwinToolchain: Toolchain {
         .appending(component: "macosx").appending(component: "prebuilt-modules")
         .appending(component: sdkInfo.versionString))
     }
+
+    // Pass down -clang-target.
+    // If not specified otherwise, we should use the same triple as -target
+    if !driver.parsedOptions.hasArgument(.disableClangTarget) &&
+        driver.isFrontendArgSupported(.clangTarget) {
+      // The common target triple for all Clang dependencies of this compilation,
+      // both direct and transitive is computed as:
+      // 1. An explicitly-specified `-clang-target` argument to this driver invocation
+      // 2. (On Darwin) The target triple of the selected SDK
+      let clangTargetTriple: String
+      if let explicitClangTripleArg = driver.parsedOptions.getLastArgument(.clangTarget)?.asSingle {
+        clangTargetTriple = explicitClangTripleArg
+      } else if let sdkPathHandle = frontendTargetInfo.sdkPath?.path,
+                let sdkPath = VirtualPath.lookup(sdkPathHandle).absolutePath,
+                let sdkInfo = Self.readSDKInfo(fileSystem, VirtualPath.absolute(sdkPath).intern()) {
+        clangTargetTriple = frontendTargetInfo.target.unversionedTriple.triple + sdkInfo.versionString
+      } else {
+        clangTargetTriple = frontendTargetInfo.target.triple.triple
+      }
+
+      commandLine.appendFlag(.clangTarget)
+      commandLine.appendFlag(clangTargetTriple)
+    }
   }
 }
 

Sources/SwiftDriver/Toolchains/Toolchain.swift

@@ -151,7 +151,7 @@ public protocol Toolchain {
     commandLine: inout [Job.ArgTemplate],
     inputs: inout [TypedVirtualPath],
     frontendTargetInfo: FrontendTargetInfo,
-    driver: Driver
+    driver: inout Driver
   ) throws
 
   var dummyForTestingObjectFormat: Triple.ObjectFormat {get}
@@ -306,7 +306,7 @@ extension Toolchain {
     commandLine: inout [Job.ArgTemplate],
     inputs: inout [TypedVirtualPath],
     frontendTargetInfo: FrontendTargetInfo,
-    driver: Driver
+    driver: inout Driver
   ) throws {}
 
   /// Resolves the path to the given tool and whether or not it supports response files so that it