cmd/go: don't try to initialize cover profile for go test -c

Using go test -c makes you responsible for managing and merging the
coverage profile yourself.

Fixes #24588

Change-Id: I2037a91ceb904f9f35d76c7b5e5fae6bcbed4e46
Reviewed-on: https://go-review.googlesource.com/103395
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/go/go_test.go

@@ -2622,6 +2622,17 @@ func TestCoverageFunc(t *testing.T) {
 	tg.grepStdoutNot(`\tf\t*[0-9]`, "reported coverage for assembly function f")
 }
 
+// Issue 24588.
+func TestCoverageDashC(t *testing.T) {
+	tg := testgo(t)
+	defer tg.cleanup()
+	tg.parallel()
+	tg.makeTempdir()
+	tg.setenv("GOPATH", filepath.Join(tg.pwd(), "testdata"))
+	tg.run("test", "-c", "-o", tg.path("coverdep"), "-coverprofile="+tg.path("no/such/dir/cover.out"), "coverdep")
+	tg.wantExecutable(tg.path("coverdep"), "go -test -c -coverprofile did not create executable")
+}
+
 func TestPluginNonMain(t *testing.T) {
 	wd, err := os.Getwd()
 	if err != nil {

src/cmd/go/internal/test/cover.go

@@ -23,7 +23,7 @@ var coverMerge struct {
 // Using this function clears the profile in case it existed from a previous run,
 // or in case it doesn't exist and the test is going to fail to create it (or not run).
 func initCoverProfile() {
-	if testCoverProfile == "" {
+	if testCoverProfile == "" || testC {
 		return
 	}
 	if !filepath.IsAbs(testCoverProfile) && testOutputDir != "" {