Building object files using -c with -lto should respect the output file path (-o) if present

Author: kubamracek

Sources/SwiftDriver/Jobs/CompileJob.swift

@@ -79,6 +79,10 @@ extension Driver {
     case .object:
       return (linkerOutputType == nil)
     case .llvmBitcode:
+      if linkerOutputType == nil {
+        return true
+      }
+
       if compilerOutputType != .llvmBitcode {
         // The compiler output isn't bitcode, so bitcode isn't top-level (-embed-bitcode).
         return false

Tests/SwiftDriverTests/SwiftDriverTests.swift

@@ -313,6 +313,27 @@ final class SwiftDriverTests: XCTestCase {
     XCTAssertEqual(driver6.compilerOutputType, .llvmBitcode)
   }
 
+  func testLtoOutputPath() throws {
+    var driver1 = try Driver(args: ["swiftc", "foo.swift", "-lto=llvm-full",
+                                    "-c", "-target", "x86_64-apple-macosx10.9"])
+    XCTAssertEqual(driver1.compilerOutputType, .llvmBitcode)
+    XCTAssertEqual(driver1.linkerOutputType, nil)
+    let jobs1 = try driver1.planBuild()
+    XCTAssertEqual(jobs1.count, 1)
+    XCTAssertEqual(jobs1[0].outputs.count, 1)
+    XCTAssertEqual(jobs1[0].outputs[0].file.basename, "foo.bc")
+
+    var driver2 = try Driver(args: ["swiftc", "foo.swift", "-lto=llvm-full",
+                                    "-c", "-target", "x86_64-apple-macosx10.9",
+                                    "-o", "foo.o"])
+    XCTAssertEqual(driver2.compilerOutputType, .llvmBitcode)
+    XCTAssertEqual(driver2.linkerOutputType, nil)
+    let jobs2 = try driver2.planBuild()
+    XCTAssertEqual(jobs2.count, 1)
+    XCTAssertEqual(jobs2[0].outputs.count, 1)
+    XCTAssertEqual(jobs2[0].outputs[0].file.basename, "foo.o")
+  }
+
   func testPrimaryOutputKindsDiagnostics() throws {
       try assertDriverDiagnostics(args: "swift", "-i") {
         $1.expect(.error("the flag '-i' is no longer required and has been removed; use 'swift input-filename'"))