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

[kubamracek]

Currently, when combining -c + -lto + -o, the driver will produce a ".bc" file on disk, even if the -o argument said ".o". This PR fixes that and matches the behavior of the C++ driver in the swift repo.

[kubamracek]

@swift-ci please test

[artemcm]

LGTM, thanks @kubamracek.

[kubamracek]

@swift-ci please test

[kubamracek]

@artemcm @compnerd could I ask for another review? I had to fix up some existing tests, and I am not super sure the change is actually correct now :)

[cltnschlosser]

Do we want this override for all cases or only for lto? There is some lto checks below:

// When -lto is set, .bc will be used for linking. Otherwise, .bc is
// top-level output (-emit-bc)
return lto == nil

Maybe?

lto == nil || linkerOutputType == nil

Looking at the tests it seems like bc is a top level output in cases where maybe it shouldn't be.
Ex: "-embed-bitcode", "-c" .bc should be intermediary output that is passed to the "backend" job to become .o. We don't need to output it next to the final outputs.

[kubamracek]

Aha, I think that's the part I was missing. This makes sense, let me adjust the PR.

[cltnschlosser]

nit: you can wrap these in do blocks to namespace the variables and not need to number everything:

Suggested change

	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")
	do {
	var driver = try Driver(args: ["swiftc", "foo.swift", "-lto=llvm-full",
	"-c", "-target", "x86_64-apple-macosx10.9"])
	XCTAssertEqual(driver.compilerOutputType, .llvmBitcode)
	XCTAssertEqual(driver.linkerOutputType, nil)
	let jobs = try driver.planBuild()
	XCTAssertEqual(jobs.count, 1)
	XCTAssertEqual(jobs[0].outputs.count, 1)
	XCTAssertEqual(jobs[0].outputs[0].file.basename, "foo.bc")
	}
	do {
	var driver = try Driver(args: ["swiftc", "foo.swift", "-lto=llvm-full",
	"-c", "-target", "x86_64-apple-macosx10.9",
	"-o", "foo.o"])
	XCTAssertEqual(driver.compilerOutputType, .llvmBitcode)
	XCTAssertEqual(driver.linkerOutputType, nil)
	let jobs = try driver.planBuild()
	XCTAssertEqual(jobs.count, 1)
	XCTAssertEqual(jobs[0].outputs.count, 1)
	XCTAssertEqual(jobs[0].outputs[0].file.basename, "foo.o")
	}

[kubamracek]

@swift-ci please test

[kubamracek]

@swift-ci please test