Forward --ld-path to linker driver (#1416)

This PR introduces an `--ld-path` option, which is forwarded to the Clang linker-driver option with the same name. This change is required to support the `toolset.linker.path` option in [SE-0387](https://github.com/apple/swift-evolution/blob/main/proposals/0387-cross-compilation-destinations.md). 

## See also

Upstream: swiftlang/swift#67956.
Downstream: swiftlang/swift-package-manager#6719.

Author: kabiroberai

Sources/SwiftDriver/Jobs/DarwinToolchain+LinkerSupport.swift

@@ -181,6 +181,8 @@ extension DarwinToolchain {
       commandLine.appendFlag("-fuse-ld=\(arg.asSingle)")
     }
 
+    try commandLine.appendLast(.ldPath, from: &parsedOptions)
+
     let fSystemArgs = parsedOptions.arguments(for: .F, .Fsystem)
     for opt in fSystemArgs {
       commandLine.appendFlag(.F)

Sources/SwiftDriver/Jobs/GenericUnixToolchain+LinkerSupport.swift

@@ -101,6 +101,8 @@ extension GenericUnixToolchain {
         }
       }
 
+      try commandLine.appendLast(.ldPath, from: &parsedOptions)
+
       // Configure the toolchain.
       //
       // By default use the system `clang` to perform the link.  We use `clang` for

Sources/SwiftDriver/Jobs/WebAssemblyToolchain+LinkerSupport.swift

@@ -43,6 +43,8 @@ extension WebAssemblyToolchain {
         commandLine.appendFlag("-fuse-ld=\(linkerArg)")
       }
 
+      try commandLine.appendLast(.ldPath, from: &parsedOptions)
+
       // Configure the toolchain.
       //
       // By default use the system `clang` to perform the link.  We use `clang` for

Sources/SwiftDriver/Jobs/WindowsToolchain+LinkerSupport.swift

@@ -105,6 +105,8 @@ extension WindowsToolchain {
       commandLine.appendFlag("-fuse-ld=lld")
     }
 
+    try commandLine.appendLast(.ldPath, from: &parsedOptions)
+
     switch lto {
     case .some(.llvmThin):
       commandLine.appendFlag("-flto=thin")

Sources/SwiftOptions/Options.swift

@@ -531,6 +531,7 @@ extension Option {
   public static let json_: Option = Option("--json", .flag, alias: Option.json, attributes: [.noDriver], helpText: "Print output in JSON format.")
   public static let j: Option = Option("-j", .joinedOrSeparate, attributes: [.doesNotAffectIncrementalBuild], metaVar: "<n>", helpText: "Number of commands to execute in parallel")
   public static let LEQ: Option = Option("-L=", .joined, alias: Option.L, attributes: [.frontend, .doesNotAffectIncrementalBuild, .argumentIsPath], group: .linkerOption)
+  public static let ldPath: Option = Option("--ld-path=", .joined, attributes: [.helpHidden, .doesNotAffectIncrementalBuild, .argumentIsPath], helpText: "Specifies the path to the linker to be used")
   public static let libc: Option = Option("-libc", .separate, attributes: [], helpText: "libc runtime library to use")
   public static let libraryLevelEQ: Option = Option("-library-level=", .joined, alias: Option.libraryLevel, attributes: [.helpHidden, .frontend, .moduleInterface], metaVar: "<level>")
   public static let libraryLevel: Option = Option("-library-level", .separate, attributes: [.helpHidden, .frontend, .moduleInterface], metaVar: "<level>", helpText: "Library distribution level 'api', 'spi' or 'other' (the default)")
@@ -758,7 +759,7 @@ extension Option {
   public static let useInterfaceForModule: Option = Option("-use-interface-for-module", .separate, attributes: [.noDriver], metaVar: "<name>", helpText: "Prefer loading these modules via interface")
   public static let useInterfaceForModule_: Option = Option("--use-interface-for-module", .separate, alias: Option.useInterfaceForModule, attributes: [.noDriver], metaVar: "<name>", helpText: "Prefer loading these modules via interface")
   public static let useJit: Option = Option("-use-jit", .flag, attributes: [.helpHidden, .frontend, .noDriver], helpText: "Register Objective-C classes as if the JIT were in use")
-  public static let useLd: Option = Option("-use-ld=", .joined, attributes: [.doesNotAffectIncrementalBuild], helpText: "Specifies the linker to be used")
+  public static let useLd: Option = Option("-use-ld=", .joined, attributes: [.doesNotAffectIncrementalBuild], helpText: "Specifies the flavor of the linker to be used")
   public static let useMalloc: Option = Option("-use-malloc", .flag, attributes: [.helpHidden, .frontend, .noDriver], helpText: "Allocate internal data structures using malloc (for memory debugging)")
   public static let useStaticResourceDir: Option = Option("-use-static-resource-dir", .flag, attributes: [.helpHidden, .frontend, .noDriver], helpText: "Use resources in the static resource directory")
   public static let useTabs: Option = Option("-use-tabs", .flag, attributes: [.noInteractive, .noBatch, .indent], helpText: "Use tabs for indentation.", group: .codeFormatting)
@@ -1327,6 +1328,7 @@ extension Option {
       Option.json_,
       Option.j,
       Option.LEQ,
+      Option.ldPath,
       Option.libc,
       Option.libraryLevelEQ,
       Option.libraryLevel,

Tests/SwiftDriverTests/SwiftDriverTests.swift

@@ -1679,7 +1679,7 @@ final class SwiftDriverTests: XCTestCase {
 
     do {
       // macOS target
-      var driver = try Driver(args: commonArgs + ["-emit-library", "-target", "x86_64-apple-macosx10.15", "-Onone", "-use-ld=foo"], env: env)
+      var driver = try Driver(args: commonArgs + ["-emit-library", "-target", "x86_64-apple-macosx10.15", "-Onone", "-use-ld=foo", "--ld-path=/bar/baz"], env: env)
       let plannedJobs = try driver.planBuild()
 
       XCTAssertEqual(3, plannedJobs.count)
@@ -1691,6 +1691,7 @@ final class SwiftDriverTests: XCTestCase {
       let cmd = linkJob.commandLine
       XCTAssertTrue(cmd.contains(.flag("-dynamiclib")))
       XCTAssertTrue(cmd.contains(.flag("-fuse-ld=foo")))
+      XCTAssertTrue(cmd.contains(.joinedOptionAndPath("--ld-path=", try VirtualPath(path: "/bar/baz"))))
       XCTAssertTrue(cmd.contains(.flag("--target=x86_64-apple-macosx10.15")))
       XCTAssertEqual(linkJob.outputs[0].file, try VirtualPath(path: "libTest.dylib"))