Revert "Revert "Only add '-fobjc-link-runtime' to the linker invocation when the driver is invoked with '-link-objc-runtime'""

This reverts commit 2dbaf86.

Author: artemcm

Sources/SwiftDriver/Jobs/DarwinToolchain+LinkerSupport.swift

@@ -214,9 +214,14 @@ 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")
+    }
+
     commandLine.appendFlags(
-      "-fobjc-link-runtime",
-      "-lobjc",
       "-lSystem"
     )
 

Tests/SwiftDriverTests/SwiftDriverTests.swift

@@ -1653,6 +1653,8 @@ final class SwiftDriverTests: XCTestCase {
 
       XCTAssertFalse(cmd.contains(.flag("-static")))
       XCTAssertFalse(cmd.contains(.flag("-shared")))
+      // Handling of '-lobjc' is now in the Clang linker driver.
+      XCTAssertFalse(cmd.contains(.flag("-lobjc")))
     }
 
     do {
@@ -1728,6 +1730,39 @@ 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.