[Toolchains] - look for tools relative to the executable path.

Sources/SwiftDriver/Toolchains/DarwinToolchain.swift

@@ -25,16 +25,16 @@ public final class DarwinToolchain: Toolchain {
   public func getToolPath(_ tool: Tool) throws -> AbsolutePath {
     switch tool {
     case .swiftCompiler:
-      return try lookup(exec: "swift")
+      return try lookup(executable: "swift")
 
     case .dynamicLinker:
-      return try lookup(exec: "ld")
+      return try lookup(executable: "ld")
 
     case .staticLinker:
-      return try lookup(exec: "libtool")
+      return try lookup(executable: "libtool")
 
     case .dsymutil:
-      return try lookup(exec: "dsymutil")
+      return try lookup(executable: "dsymutil")
 
     case .clang:
       let result = try Process.checkNonZeroExit(
@@ -43,13 +43,13 @@ public final class DarwinToolchain: Toolchain {
       ).spm_chomp()
       return AbsolutePath(result)
     case .swiftAutolinkExtract:
-      return try lookup(exec: "swift-autolink-extract")
+      return try lookup(executable: "swift-autolink-extract")
     }
   }
 
   /// Swift compiler path.
   public lazy var swiftCompiler: Result<AbsolutePath, Swift.Error> = Result {
-    try lookup(exec: "swift")
+    try lookup(executable: "swift")
   }
 
   /// SDK path.

Sources/SwiftDriver/Toolchains/GenericUnixToolchain.swift

@@ -30,18 +30,18 @@ public final class GenericUnixToolchain: Toolchain {
   public func getToolPath(_ tool: Tool) throws -> AbsolutePath {
     switch tool {
     case .swiftCompiler:
-      return try lookup(exec: "swift")
+      return try lookup(executable: "swift")
     case .staticLinker:
-      return try lookup(exec: "ar")
+      return try lookup(executable: "ar")
     case .dynamicLinker:
       // FIXME: This needs to look in the tools_directory first.
-      return try lookup(exec: "clang")
+      return try lookup(executable: "clang")
     case .clang:
-      return try lookup(exec: "clang")
+      return try lookup(executable: "clang")
     case .swiftAutolinkExtract:
-      return try lookup(exec: "swift-autolink-extract")
+      return try lookup(executable: "swift-autolink-extract")
     case .dsymutil:
-      return try lookup(exec: "dsymutil")
+      return try lookup(executable: "dsymutil")
     }
   }
 

Sources/SwiftDriver/Toolchains/Toolchain.swift

@@ -101,34 +101,35 @@ extension Toolchain {
     return "SWIFT_DRIVER_\(toolName.uppercased())_EXEC"
   }
 
-  /// Looks for the executable in the `SWIFT_DRIVER_TOOLNAME_EXEC` enviroment variable, if found nothing,
+  /// Looks for the executable in the `SWIFT_DRIVER_TOOLNAME_EXEC` environment variable, if found nothing,
   /// looks in the `executableDir`, `xcrunFind` or in the `searchPaths`.
-  /// - Parameter exec: executable to look for [i.e. `swift`].
-  func lookup(exec: String) throws -> AbsolutePath {
-    if let overrideString = envVar(forExecutable: exec) {
+  /// - Parameter executable: executable to look for [i.e. `swift`].
+  func lookup(executable: String) throws -> AbsolutePath {
+    if let overrideString = envVar(forExecutable: executable) {
       return try AbsolutePath(validating: overrideString)
-    } else if let path = lookupExecutablePath(filename: exec, searchPaths: [executableDir]) {
+    } else if let path = lookupExecutablePath(filename: executable, searchPaths: [executableDir]) {
       return path
-    } else if let path = try? xcrunFind(exec: exec) {
+    } else if let path = try? xcrunFind(executable: executable) {
       return path
-    } else if let path = lookupExecutablePath(filename: exec, searchPaths: searchPaths) {
+    } else if let path = lookupExecutablePath(filename: executable, searchPaths: searchPaths) {
       return path
     } else {
-      // This is a hack so our tests work on linux. We need a better way for looking up tools in general.
-      return AbsolutePath("/usr/bin/" + exec)
+      // This is a hack so our tests work on linux.
+      return AbsolutePath("/usr/bin/" + executable)
     }
   }
 
-  private func xcrunFind(exec: String) throws -> AbsolutePath {
-  #if os(macOS)
+  private func xcrunFind(executable: String) throws -> AbsolutePath {
+    let xcrun = "xcrun"
+    guard lookupExecutablePath(filename: xcrun, searchPaths: searchPaths) != nil else {
+      throw ToolchainError.unableToFind(tool: xcrun)
+    }
+
     let path = try Process.checkNonZeroExit(
-      arguments: ["xcrun", "-sdk", "macosx", "--find", exec],
+      arguments: [xcrun, "-sdk", "macosx", "--find", executable],
       environment: env
     ).spm_chomp()
     return AbsolutePath(path)
-  #else
-    throw ToolchainError.unableToFind(tool: exec)
-  #endif
   }
 }