Remove unnecessarily hard-coded executable suffix

... and also clarify about that in documentation.

Author: stevapple

Sources/SwiftDriver/Jobs/WindowsToolchain+LinkerSupport.swift

@@ -44,9 +44,9 @@ extension WindowsToolchain {
       let librarian: String
       switch parsedOptions.getLastArgument(.useLd)?.asSingle {
       case .none:
-        librarian = lto == nil ? "link.exe" : "lld-link.exe"
+        librarian = lto == nil ? "link" : "lld-link"
       case .some("lld"), .some("lld.exe"), .some("lld-link"), .some("lld-link.exe"):
-        librarian = "lld-link.exe"
+        librarian = "lld-link"
       case let .some(linker):
         librarian = linker
       }

Sources/SwiftDriver/Toolchains/Toolchain.swift

@@ -191,11 +191,7 @@ extension Toolchain {
 
   /// - Returns: String in the form of: `SWIFT_DRIVER_TOOLNAME_EXEC`
   private func envVarName(for toolName: String) -> String {
-    var lookupName = toolName
-#if os(Windows)
-    lookupName = lookupName.replacingOccurrences(of: ".exe", with: "")
-#endif
-    lookupName = lookupName.replacingOccurrences(of: "-", with: "_").uppercased()
+    let lookupName = toolName.replacingOccurrences(of: "-", with: "_").uppercased()
     return "SWIFT_DRIVER_\(lookupName)_EXEC"
   }
 
@@ -209,9 +205,9 @@ extension Toolchain {
 
   /// 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 executable: executable to look for [i.e. `swift`].
+  /// - Parameter executable: executable to look for [i.e. `swift`]. Executable suffix (eg. `.exe`) should be omitted.
   func lookup(executable: String) throws -> AbsolutePath {
-    if let overrideString = envVar(forExecutable: executableName(executable)) {
+    if let overrideString = envVar(forExecutable: executable) {
       return try AbsolutePath(validating: overrideString)
     } else if let toolDir = toolDirectory,
               let path = lookupExecutablePath(filename: executableName(executable), searchPaths: [toolDir]) {
@@ -221,7 +217,7 @@ extension Toolchain {
       return path
     } else if let path = try? xcrunFind(executable: executableName(executable)) {
       return path
-    } else if !["swift-frontend", "swift", "swift-frontend.exe", "swift.exe"].contains(executable),
+    } else if !["swift-frontend", "swift"].contains(executable),
               let parentDirectory = try? getToolPath(.swiftCompiler).parentDirectory,
               parentDirectory != executableDir,
               let path = lookupExecutablePath(filename: executableName(executable), searchPaths: [parentDirectory]) {
@@ -230,14 +226,14 @@ extension Toolchain {
       return path
     } else if let path = lookupExecutablePath(filename: executableName(executable), searchPaths: searchPaths) {
       return path
-    } else if executable == executableName("swift-frontend") {
+    } else if executable == "swift-frontend" {
       // Temporary shim: fall back to looking for "swift" before failing.
-      return try lookup(executable: executableName("swift"))
+      return try lookup(executable: "swift")
     } else if fallbackToExecutableDefaultPath {
       if self is WindowsToolchain {
         return try getToolPath(.swiftCompiler)
                 .parentDirectory
-                .appending(component: executable)
+                .appending(component: executableName(executable))
       } else {
         return AbsolutePath("/usr/bin/" + executable)
       }

Sources/SwiftDriver/Toolchains/WindowsToolchain.swift

@@ -69,27 +69,27 @@ extension WindowsToolchain.ToolchainValidationError {
   private func lookupToolPath(_ tool: Tool) throws -> AbsolutePath {
     switch tool {
     case .swiftAPIDigester:
-      return try lookup(executable: "swift-api-digester.exe")
+      return try lookup(executable: "swift-api-digester")
     case .swiftCompiler:
-      return try lookup(executable: "swift-frontend.exe")
+      return try lookup(executable: "swift-frontend")
     case .staticLinker:
-      return try lookup(executable: "lld-link.exe")
+      return try lookup(executable: "lld-link")
     case .dynamicLinker:
-      return try lookup(executable: "clang.exe")
+      return try lookup(executable: "clang")
     case .clang:
-      return try lookup(executable: "clang.exe")
+      return try lookup(executable: "clang")
     case .clangxx:
-      return try lookup(executable: "clang++.exe")
+      return try lookup(executable: "clang++")
     case .swiftAutolinkExtract:
-      return try lookup(executable: "swift-autolink-extract.exe")
+      return try lookup(executable: "swift-autolink-extract")
     case .lldb:
-      return try lookup(executable: "lldb.exe")
+      return try lookup(executable: "lldb")
     case .dsymutil:
-      return try lookup(executable: "llvm-dsymutil.exe")
+      return try lookup(executable: "llvm-dsymutil")
     case .dwarfdump:
-      return try lookup(executable: "llvm-dwarfdump.exe")
+      return try lookup(executable: "llvm-dwarfdump")
     case .swiftHelp:
-      return try lookup(executable: "swift-help.exe")
+      return try lookup(executable: "swift-help")
     }
   }