Remove support for linking arclite

Darwin no longer uses arclite and it's no longer distributed in the macOS SDKs.

This leaves the options '-link-objc-runtime' and '-no-link-objc-runtime' in place, but strips out all the logic that actually used them.

Part of: rdar://105406972

Author: artemcm

Sources/SwiftDriver/Driver/Driver.swift

@@ -2831,6 +2831,10 @@ extension Driver {
         diagnosticsEngine.emit(.error_hermetic_seal_requires_lto)
       }
     }
+    if parsedOptions.hasArgument(.linkObjcRuntime) ||
+        parsedOptions.hasArgument(.noLinkObjcRuntime) {
+      diagnosticsEngine.emit(.warning_darwin_link_objc_deprecated())
+    }
   }
 
   private static func validateSanitizerAddressUseOdrIndicatorFlag(

Sources/SwiftDriver/Jobs/DarwinToolchain+LinkerSupport.swift

@@ -16,38 +16,6 @@ import struct TSCBasic.AbsolutePath
 import struct TSCBasic.RelativePath
 
 extension DarwinToolchain {
-  internal func findXcodeClangPath() throws -> AbsolutePath? {
-    let result = try executor.checkNonZeroExit(
-      args: "xcrun", "-toolchain", "default", "-f", "clang",
-      environment: env
-    ).trimmingCharacters(in: .whitespacesAndNewlines)
-
-    return result.isEmpty ? nil : try AbsolutePath(validating: result)
-  }
-
-  internal func findXcodeClangLibPath(_ additionalPath: String) throws -> AbsolutePath? {
-    let path = try getToolPath(.swiftCompiler)
-      .parentDirectory // 'swift'
-      .parentDirectory // 'bin'
-      .appending(components: "lib", additionalPath)
-
-    if fileSystem.exists(path) { return path }
-
-    // If we don't have a 'lib/arc/' directory, find the "arclite" library
-    // relative to the Clang in the active Xcode.
-    if let clangPath = try? findXcodeClangPath() {
-      return clangPath
-        .parentDirectory // 'clang'
-        .parentDirectory // 'bin'
-        .appending(components: "lib", additionalPath)
-    }
-    return nil
-  }
-
-  internal func findARCLiteLibPath() throws -> AbsolutePath? {
-    return try findXcodeClangLibPath("arc")
-  }
-
   /// Adds the arguments necessary to link the files from the given set of
   /// options for a Darwin platform.
   public func addPlatformSpecificLinkerArgs(
@@ -219,13 +187,6 @@ extension DarwinToolchain {
       commandLine.appendPath(VirtualPath.lookup(sdkPath))
     }
 
-    // -link-objc-runtime also implies -fobjc-link-runtime
-    if parsedOptions.hasFlag(positive: .linkObjcRuntime,
-                             negative: .noLinkObjcRuntime,
-                             default: false) {
-      commandLine.appendFlag("-fobjc-link-runtime")
-    }
-
     let targetTriple = targetInfo.target.triple
     commandLine.appendFlag("--target=\(targetTriple.triple)")
     if let variantTriple = targetInfo.targetVariant?.triple {

Sources/SwiftDriver/Toolchains/DarwinToolchain.swift

@@ -188,14 +188,6 @@ public final class DarwinToolchain: Toolchain {
                            targetVariantTriple: Triple?,
                            compilerOutputType: FileType?,
                            diagnosticsEngine: DiagnosticsEngine) throws {
-    // On non-darwin hosts, libArcLite won't be found and a warning will be emitted
-    // Guard for the sake of tests running on all platforms
-    #if canImport(Darwin)
-    // Validating arclite library path when link-objc-runtime.
-    validateLinkObjcRuntimeARCLiteLib(&parsedOptions,
-                                      targetTriple: targetTriple,
-                                      diagnosticsEngine: diagnosticsEngine)
-    #endif
     // Validating apple platforms deployment targets.
     try validateDeploymentTarget(&parsedOptions, targetTriple: targetTriple, 
                                  compilerOutputType: compilerOutputType)
@@ -247,22 +239,6 @@ public final class DarwinToolchain: Toolchain {
       }
     }
   }
-    
-  func validateLinkObjcRuntimeARCLiteLib(_ parsedOptions: inout ParsedOptions,
-                                           targetTriple: Triple,
-                                           diagnosticsEngine: DiagnosticsEngine) {
-    guard parsedOptions.hasFlag(positive: .linkObjcRuntime,
-                                negative: .noLinkObjcRuntime,
-                                default: !targetTriple.supports(.nativeARC))
-    else {
-      return
-    }
-
-    guard let _ = try? findARCLiteLibPath() else {
-        diagnosticsEngine.emit(.warn_arclite_not_found_when_link_objc_runtime)
-        return
-    }
-  }
 
   struct DarwinSDKInfo: Decodable {
     private enum CodingKeys: String, CodingKey {
@@ -404,15 +380,6 @@ public final class DarwinToolchain: Toolchain {
   }
 }
 
-extension Diagnostic.Message {
-    static var warn_arclite_not_found_when_link_objc_runtime: Diagnostic.Message {
-      .warning(
-        "unable to find Objective-C runtime support library 'arclite'; " +
-        "pass '-no-link-objc-runtime' to silence this warning"
-      )
-    }
-}
-
 private extension Version {
   var sdkVersionString: String {
     if patch == 0 && prerelease.isEmpty && metadata.isEmpty {

Sources/SwiftDriver/Utilities/Diagnostics.swift

@@ -51,6 +51,10 @@ extension Diagnostic.Message {
     .warning("inferring simulator environment for target '\(originalTriple.triple)'; use '-target \(inferredTriple.triple)' instead")
   }
 
+  static func warning_darwin_link_objc_deprecated() -> Diagnostic.Message {
+    .warning("-link-objc-runtime is no longer supported on Apple platforms")
+  }
+
   static func error_argument_not_allowed_with(arg: String, other: String) -> Diagnostic.Message {
     .error("argument '\(arg)' is not allowed with '\(other)'")
   }

Sources/SwiftDriver/Utilities/Triple+Platforms.swift

@@ -398,25 +398,3 @@ extension Triple {
     }
   }
 }
-
-extension Triple.FeatureAvailability {
-  /// Linking `libarclite` is unnecessary for triples supporting this feature.
-  ///
-  /// This impacts the `-link-objc-runtime` flag in Swift, which is akin to the
-  /// `-fobjc-link-runtime` build setting in clang. When set, these flags
-  /// automatically link libobjc, and any compatibility libraries that don't
-  /// ship with the OS. The versions here are the first OSes that support
-  /// ARC natively in their respective copies of the Objective-C runtime,
-  /// and therefore do not require additional support libraries.
-  static let nativeARC = Self(
-    macOS: .available(since: Triple.Version(10, 11, 0)),
-    iOS: .available(since: Triple.Version(9, 0, 0)),
-    tvOS: .available(since: Triple.Version(9, 0, 0)),
-    watchOS: .availableInAllVersions
-  )
-  // When updating the versions listed here, please record the most recent
-  // feature being depended on and when it was introduced:
-  //
-  // - Make assigning 'nil' to an NSMutableDictionary subscript delete the
-  //   entry, like it does for Swift.Dictionary, rather than trap.
-}

Tests/SwiftDriverTests/SwiftDriverTests.swift

@@ -601,6 +601,15 @@ final class SwiftDriverTests: XCTestCase {
     }
   }
 
+  func testLinkObjCFlagWarning() throws {
+    try assertDriverDiagnostics(args: "swiftc", "foo.swift", "-link-objc-runtime") {
+      $1.expect(.warning("-link-objc-runtime is no longer supported on Apple platforms"))
+    }
+    try assertDriverDiagnostics(args: "swiftc", "foo.swift", "-no-link-objc-runtime") {
+      $1.expect(.warning("-link-objc-runtime is no longer supported on Apple platforms"))
+    }
+  }
+
   func testHermeticSealAtLink() throws {
     try assertNoDriverDiagnostics(args: "swiftc", "foo.swift", "-experimental-hermetic-seal-at-link", "-lto=llvm-full") { driver in
       let jobs = try driver.planBuild()
@@ -1761,39 +1770,6 @@ final class SwiftDriverTests: XCTestCase {
       XCTAssertFalse(cmd.contains(.flag("-shared")))
     }
 
-    do {
-      // -fobjc-link-runtime default
-      var driver = try Driver(args: commonArgs + ["-emit-library", "-target", "x86_64-apple-macosx10.15"], env: env)
-      let plannedJobs = try driver.planBuild()
-      XCTAssertEqual(3, plannedJobs.count)
-      let linkJob = plannedJobs[2]
-      XCTAssertEqual(linkJob.kind, .link)
-      let cmd = linkJob.commandLine
-      XCTAssertFalse(cmd.contains(.flag("-fobjc-link-runtime")))
-    }
-
-    do {
-      // -fobjc-link-runtime enable
-      var driver = try Driver(args: commonArgs + ["-emit-library", "-target", "x86_64-apple-macosx10.15", "-link-objc-runtime"], env: env)
-      let plannedJobs = try driver.planBuild()
-      XCTAssertEqual(3, plannedJobs.count)
-      let linkJob = plannedJobs[2]
-      XCTAssertEqual(linkJob.kind, .link)
-      let cmd = linkJob.commandLine
-      XCTAssertTrue(cmd.contains(.flag("-fobjc-link-runtime")))
-    }
-
-    do {
-      // -fobjc-link-runtime disable override
-      var driver = try Driver(args: commonArgs + ["-emit-library", "-target", "x86_64-apple-macosx10.15", "-link-objc-runtime", "-no-link-objc-runtime"], env: env)
-      let plannedJobs = try driver.planBuild()
-      XCTAssertEqual(3, plannedJobs.count)
-      let linkJob = plannedJobs[2]
-      XCTAssertEqual(linkJob.kind, .link)
-      let cmd = linkJob.commandLine
-      XCTAssertFalse(cmd.contains(.flag("-fobjc-link-runtime")))
-    }
-
     do {
       // Xlinker flags
       // Ensure that Xlinker flags are passed as such to the clang linker invocation.
@@ -3824,11 +3800,6 @@ final class SwiftDriverTests: XCTestCase {
 
     // Ensure arm64_32 is not restricted to back-deployment like other 32-bit archs (armv7k/i386).
     XCTAssertNoThrow(try Driver(args: ["swiftc", "-emit-module", "-c", "-target", "arm64_32-apple-watchos12.0", "foo.swift"]))
-
-    // On non-darwin hosts, libArcLite won't be found and a warning will be emitted
-    #if os(macOS)
-    try assertNoDriverDiagnostics(args: "swiftc", "-c", "-target", "x86_64-apple-macosx10.14", "-link-objc-runtime", "foo.swift")
-    #endif
   }
 
   func testProfileArgValidation() throws {