cmd/vet: parallelize tests

Was 2.3 seconds. Now 1.4 seconds.

Next win would be not running a child process and refactoring main so
it could be called from tests easily. But that would also require
rewriting the errchk written in Perl. This appears to be the last user
of errchk in the tree.

Updates #17751

Change-Id: Id7c3cec76f438590789b994e756f55b5397be07f
Reviewed-on: https://go-review.googlesource.com/32754
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>

src/cmd/vet/testdata/testingpkg/tests.go

@@ -0,0 +1 @@
+package testdata

src/cmd/vet/vet_test.go

@@ -13,6 +13,7 @@ import (
 	"os/exec"
 	"path/filepath"
 	"runtime"
+	"sync"
 	"testing"
 )
 
@@ -40,19 +41,22 @@ func MustHavePerl(t *testing.T) {
 }
 
 var (
+	buildMu sync.Mutex // guards following
 	built   = false    // We have built the binary.
 	failed  = false    // We have failed to build the binary, don't try again.
 )
 
 func Build(t *testing.T) {
-	testenv.MustHaveGoBuild(t)
-	MustHavePerl(t)
+	buildMu.Lock()
+	defer buildMu.Unlock()
 	if built {
 		return
 	}
 	if failed {
 		t.Skip("cannot run on this environment")
 	}
+	testenv.MustHaveGoBuild(t)
+	MustHavePerl(t)
 	cmd := exec.Command(testenv.GoToolPath(t), "build", "-o", binary)
 	output, err := cmd.CombinedOutput()
 	if err != nil {
@@ -83,52 +87,104 @@ func Vet(t *testing.T, files []string) {
 // 	rm testvet
 //
 
+// TestVet tests self-contained files in testdata/*.go.
+//
+// If a file contains assembly or has inter-dependencies, it should be
+// in its own test, like TestVetAsm, TestDivergentPackagesExamples,
+// etc below.
 func TestVet(t *testing.T) {
 	Build(t)
+	t.Parallel()
 
 	// errchk ./testvet
 	gos, err := filepath.Glob(filepath.Join(dataDir, "*.go"))
 	if err != nil {
 		t.Fatal(err)
 	}
-	asms, err := filepath.Glob(filepath.Join(dataDir, "*.s"))
+	wide := runtime.GOMAXPROCS(0)
+	if wide > len(gos) {
+		wide = len(gos)
+	}
+	batch := make([][]string, wide)
+	for i, file := range gos {
+		batch[i%wide] = append(batch[i%wide], file)
+	}
+	for i, files := range batch {
+		files := files
+		t.Run(fmt.Sprint(i), func(t *testing.T) {
+			t.Parallel()
+			t.Logf("files: %q", files)
+			Vet(t, files)
+		})
+	}
+}
+
+func TestVetAsm(t *testing.T) {
+	Build(t)
+
+	asmDir := filepath.Join(dataDir, "asm")
+	gos, err := filepath.Glob(filepath.Join(asmDir, "*.go"))
 	if err != nil {
 		t.Fatal(err)
 	}
-	files := append(gos, asms...)
-	Vet(t, files)
+	asms, err := filepath.Glob(filepath.Join(asmDir, "*.s"))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	t.Parallel()
+	// errchk ./testvet
+	Vet(t, append(gos, asms...))
 }
 
-func TestDivergentPackagesExamples(t *testing.T) {
+func TestVetDirs(t *testing.T) {
+	t.Parallel()
 	Build(t)
-	// errchk ./testvet
-	Vet(t, []string{"testdata/divergent"})
-}
-
-func TestIncompleteExamples(t *testing.T) {
-	Build(t)
-	// errchk ./testvet
-	Vet(t, []string{"testdata/incomplete/examples_test.go"})
+	for _, dir := range []string{
+		"testingpkg",
+		"divergent",
+		"buildtag",
+		"incomplete", // incomplete examples
+	} {
+		dir := dir
+		t.Run(dir, func(t *testing.T) {
+			t.Parallel()
+			gos, err := filepath.Glob(filepath.Join("testdata", dir, "*.go"))
+			if err != nil {
+				t.Fatal(err)
+			}
+			Vet(t, gos)
+		})
+	}
 }
 
 func run(c *exec.Cmd, t *testing.T) bool {
 	output, err := c.CombinedOutput()
-	os.Stderr.Write(output)
 	if err != nil {
+		t.Logf("vet output:\n%s", output)
 		t.Fatal(err)
 	}
 	// Errchk delights by not returning non-zero status if it finds errors, so we look at the output.
 	// It prints "BUG" if there is a failure.
 	if !c.ProcessState.Success() {
+		t.Logf("vet output:\n%s", output)
 		return false
 	}
-	return !bytes.Contains(output, []byte("BUG"))
+	ok := !bytes.Contains(output, []byte("BUG"))
+	if !ok {
+		t.Logf("vet output:\n%s", output)
+	}
+	return ok
 }
 
 // TestTags verifies that the -tags argument controls which files to check.
 func TestTags(t *testing.T) {
+	t.Parallel()
 	Build(t)
 	for _, tag := range []string{"testtag", "x testtag y", "x,testtag,y"} {
+		tag := tag
+		t.Run(tag, func(t *testing.T) {
+			t.Parallel()
 			t.Logf("-tags=%s", tag)
 			args := []string{
 				"-tags=" + tag,
@@ -147,5 +203,6 @@ func TestTags(t *testing.T) {
 			if bytes.Contains(output, []byte(filepath.Join("tagtest", "file2.go"))) {
 				t.Error("file2 was included, should be excluded")
 			}
+		})
 	}
 }