Pass Swift compiler path to Toolchain.swiftCompilerVersion().

Allows overridden Swift compiler frontend paths to work.

Author: DougGregor

Sources/SwiftDriver/Driver/Driver.swift

@@ -286,7 +286,8 @@ public struct Driver {
       moduleOutput: self.moduleOutput,
       inputFiles: inputFiles,
       diagnosticEngine: diagnosticEngine,
-      actualSwiftVersion: try? toolchain.swiftCompilerVersion()
+      actualSwiftVersion:
+        try? toolchain.swiftCompilerVersion(self.swiftCompiler)
     )
 
     self.sdkPath = Self.computeSDKPath(&parsedOptions, compilerMode: compilerMode, toolchain: toolchain, diagnosticsEngine: diagnosticEngine, env: env)

Sources/SwiftDriver/Toolchains/Toolchain.swift

@@ -74,10 +74,10 @@ extension Toolchain {
     getEnvSearchPaths(pathString: env["PATH"], currentWorkingDirectory: localFileSystem.currentWorkingDirectory)
   }
 
-  public func swiftCompilerVersion() throws -> String {
+  public func swiftCompilerVersion(_ swiftCompiler: VirtualPath) throws -> String {
     // FIXME: Thread the driver's swiftCompiler path here.
     try Process.checkNonZeroExit(
-      args: getToolPath(.swiftCompiler).pathString, "-version",
+      args: swiftCompiler.name, "-version",
       environment: env
     ).split(separator: "\n").first.map(String.init) ?? ""
   }

Tests/SwiftDriverTests/SwiftDriverTests.swift

@@ -1168,8 +1168,12 @@ final class SwiftDriverTests: XCTestCase {
   }
 
   func testToolchainUtilities() throws {
-    let darwinSwiftVersion = try DarwinToolchain(env: ProcessEnv.vars).swiftCompilerVersion()
-    let unixSwiftVersion = try GenericUnixToolchain(env: ProcessEnv.vars).swiftCompilerVersion()
+    let darwinToolchain = DarwinToolchain(env: ProcessEnv.vars)
+    let darwinSwiftVersion = try darwinToolchain.swiftCompilerVersion(
+      .absolute(darwinToolchain.getToolPath(.swiftCompiler)))
+    let unixToolchain =  GenericUnixToolchain(env: ProcessEnv.vars)
+    let unixSwiftVersion = try unixToolchain.swiftCompilerVersion(
+      .absolute(unixToolchain.getToolPath(.swiftCompiler)))
     assertString(darwinSwiftVersion, contains: "Swift version ")
     assertString(unixSwiftVersion, contains: "Swift version ")
   }