Merge pull request #1744 from tshortli/revert-1741

Revert "swift-driver: correct the legacy driver path construction"

This is breaking PR testing, so we should revert it.

Author: al45tair

Sources/swift-driver/main.swift

@@ -25,7 +25,6 @@ import Android
 #endif
 
 import Dispatch
-import Foundation
 
 #if os(Windows)
 import WinSDK
@@ -74,18 +73,13 @@ do {
   // Fallback to legacy driver if forced to
   if CommandLine.arguments.contains(Option.disallowForwardingDriver.spelling) ||
      ProcessEnv.vars["SWIFT_USE_OLD_DRIVER"] != nil {
-    let executable: URL = URL(fileURLWithPath: CommandLine.arguments[0])
-    let legacyExecutablePath: URL =
-        executable.deletingLastPathComponent()
-                  .appendingPathComponent("\(executable.deletingPathExtension().lastPathComponent)-legacy-driver")
-                  .appendingPathExtension(executable.pathExtension)
-    let path: String = legacyExecutablePath.withUnsafeFileSystemRepresentation { String(cString: $0!) }
-
-    if localFileSystem.exists(AbsolutePath(path)) {
-      let legacyDriverCommand = [path] + CommandLine.arguments[1...]
-      try exec(path: path, args: legacyDriverCommand)
+    if let legacyExecutablePath = Process.findExecutable(CommandLine.arguments[0] + "-legacy-driver"),
+       localFileSystem.exists(legacyExecutablePath) {
+      let legacyDriverCommand = [legacyExecutablePath.pathString] +
+                                  CommandLine.arguments[1...]
+      try exec(path: legacyExecutablePath.pathString, args: legacyDriverCommand)
     } else {
-      throw Driver.Error.unknownOrMissingSubcommand(legacyExecutablePath.lastPathComponent)
+      throw Driver.Error.unknownOrMissingSubcommand(CommandLine.arguments[0] + "-legacy-driver")
     }
   }