cmd/go: updates go get to return exit status 0 for test file only pkgs

Updates the behavior of `go get` to return exit status 0 when a
requested package only contains test files.

Fixes #15093

Change-Id: I76b80517d58748090f5e8c6f41178361e2d7ca54
Reviewed-on: https://go-review.googlesource.com/23314Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/go/build.go

@@ -579,6 +579,10 @@ func libname(args []string, pkgs []*Package) (string, error) {
 }
 
 func runInstall(cmd *Command, args []string) {
+	installPackages(args, false)
+}
+
+func installPackages(args []string, forGet bool) {
 	if gobin != "" && !filepath.IsAbs(gobin) {
 		fatalf("cannot install, GOBIN must be an absolute path")
 	}
@@ -606,6 +610,8 @@ func runInstall(cmd *Command, args []string) {
 
 	var b builder
 	b.init()
+	// Set the behavior for `go get` to not error on packages with test files only.
+	b.testFilesOnlyOK = forGet
 	var a *action
 	if buildBuildmode == "shared" {
 		if libName, err := libname(args, pkgs); err != nil {
@@ -696,6 +702,8 @@ type builder struct {
 	flagCache   map[string]bool      // a cache of supported compiler flags
 	print       func(args ...interface{}) (int, error)
 
+	testFilesOnlyOK bool // do not error if the packages only have test files
+
 	output    sync.Mutex
 	scriptDir string // current directory in printed script
 
@@ -1279,6 +1287,8 @@ func (b *builder) do(root *action) {
 		if err != nil {
 			if err == errPrintedOutput {
 				setExitStatus(2)
+			} else if _, ok := err.(*build.NoGoError); ok && len(a.p.TestGoFiles) > 0 && b.testFilesOnlyOK {
+				// Ignore the "no buildable Go source files" error for a package with only test files.
 			} else {
 				errorf("%s", err)
 			}
@@ -1365,7 +1375,7 @@ func (b *builder) build(a *action) (err error) {
 	}
 
 	defer func() {
-		if err != nil && err != errPrintedOutput {
+		if _, ok := err.(*build.NoGoError); err != nil && err != errPrintedOutput && !(ok && b.testFilesOnlyOK && len(a.p.TestGoFiles) > 0) {
 			err = fmt.Errorf("go build %s: %v", a.p.ImportPath, err)
 		}
 	}()

src/cmd/go/get.go

@@ -139,7 +139,7 @@ func runGet(cmd *Command, args []string) {
 		return
 	}
 
-	runInstall(cmd, args)
+	installPackages(args, true)
 }
 
 // downloadPaths prepares the list of paths to pass to download.

src/cmd/go/go_test.go

@@ -1430,6 +1430,17 @@ func TestGoGetNonPkg(t *testing.T) {
 	tg.grepStderr("golang.org/x/tools: no buildable Go source files", "missing error")
 }
 
+func TestGoGetTestOnlyPkg(t *testing.T) {
+	testenv.MustHaveExternalNetwork(t)
+
+	tg := testgo(t)
+	defer tg.cleanup()
+	tg.tempDir("gopath")
+	tg.setenv("GOPATH", tg.path("gopath"))
+	tg.run("get", "golang.org/x/tour/content")
+	tg.run("get", "-t", "golang.org/x/tour/content")
+}
+
 func TestInstalls(t *testing.T) {
 	if testing.Short() {
 		t.Skip("don't install into GOROOT in short mode")