cmd/go: use internal/testenv instead of computing canRun and skipExternal ad-hoc

Fixes #42223

Change-Id: Icf9bb61d48f0a6c7fd6f74e80e333a4837aa52ab
Reviewed-on: https://go-review.googlesource.com/c/go/+/265781
Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/go/go_test.go

@@ -35,72 +35,29 @@ import (
 )
 
 var (
-	canRun  = true  // whether we can run go or ./testgo
 	canRace = false // whether we can run the race detector
 	canCgo  = false // whether we can use cgo
 	canMSan = false // whether we can run the memory sanitizer
-
-	exeSuffix string // ".exe" on Windows
-
-	skipExternal = false // skip external tests
 )
 
+var exeSuffix string = func() string {
+	if runtime.GOOS == "windows" {
+		return ".exe"
+	}
+	return ""
+}()
+
 func tooSlow(t *testing.T) {
 	if testing.Short() {
 		// In -short mode; skip test, except run it on the {darwin,linux,windows}/amd64 builders.
 		if testenv.Builder() != "" && runtime.GOARCH == "amd64" && (runtime.GOOS == "linux" || runtime.GOOS == "darwin" || runtime.GOOS == "windows") {
 			return
 		}
+		t.Helper()
 		t.Skip("skipping test in -short mode")
 	}
 }
 
-func init() {
-	switch runtime.GOOS {
-	case "android", "js":
-		canRun = false
-	case "darwin":
-		// nothing to do
-	case "ios":
-		canRun = false
-	case "linux":
-		switch runtime.GOARCH {
-		case "arm":
-			// many linux/arm machines are too slow to run
-			// the full set of external tests.
-			skipExternal = true
-		case "mips", "mipsle", "mips64", "mips64le":
-			// Also slow.
-			skipExternal = true
-			if testenv.Builder() != "" {
-				// On the builders, skip the cmd/go
-				// tests. They're too slow and already
-				// covered by other ports. There's
-				// nothing os/arch specific in the
-				// tests.
-				canRun = false
-			}
-		}
-	case "freebsd":
-		switch runtime.GOARCH {
-		case "arm":
-			// many freebsd/arm machines are too slow to run
-			// the full set of external tests.
-			skipExternal = true
-			canRun = false
-		}
-	case "plan9":
-		switch runtime.GOARCH {
-		case "arm":
-			// many plan9/arm machines are too slow to run
-			// the full set of external tests.
-			skipExternal = true
-		}
-	case "windows":
-		exeSuffix = ".exe"
-	}
-}
-
 // testGOROOT is the GOROOT to use when running testgo, a cmd/go binary
 // build from this process's current GOROOT, but run from a different
 // (temp) directory.
@@ -153,7 +110,7 @@ func TestMain(m *testing.M) {
 	}
 
 	testGOCACHE = cache.DefaultDir()
-	if canRun {
+	if testenv.HasGoBuild() {
 		testBin = filepath.Join(testTmpDir, "testbin")
 		if err := os.Mkdir(testBin, 0777); err != nil {
 			log.Fatal(err)
@@ -224,7 +181,7 @@ func TestMain(m *testing.M) {
 		cmd.Stderr = new(strings.Builder)
 		if out, err := cmd.Output(); err != nil {
 			fmt.Fprintf(os.Stderr, "running testgo failed: %v\n%s", err, cmd.Stderr)
-			canRun = false
+			os.Exit(2)
 		} else {
 			canCgo, err = strconv.ParseBool(strings.TrimSpace(string(out)))
 			if err != nil {
@@ -324,10 +281,7 @@ func skipIfGccgo(t *testing.T, msg string) {
 func testgo(t *testing.T) *testgoData {
 	t.Helper()
 	testenv.MustHaveGoBuild(t)
-
-	if skipExternal {
-		t.Skipf("skipping external tests on %s/%s", runtime.GOOS, runtime.GOARCH)
-	}
+	testenv.SkipIfShortAndSlow(t)
 
 	return &testgoData{t: t}
 }
@@ -416,9 +370,6 @@ func (tg *testgoData) goTool() string {
 // returning exit status.
 func (tg *testgoData) doRun(args []string) error {
 	tg.t.Helper()
-	if !canRun {
-		panic("testgoData.doRun called but canRun false")
-	}
 	if tg.inParallel {
 		for _, arg := range args {
 			if strings.HasPrefix(arg, "testdata") || strings.HasPrefix(arg, "./testdata") {

src/cmd/go/script_test.go

@@ -40,9 +40,7 @@ import (
 // TestScript runs the tests in testdata/script/*.txt.
 func TestScript(t *testing.T) {
 	testenv.MustHaveGoBuild(t)
-	if skipExternal {
-		t.Skipf("skipping external tests on %s/%s", runtime.GOOS, runtime.GOARCH)
-	}
+	testenv.SkipIfShortAndSlow(t)
 
 	files, err := filepath.Glob("testdata/script/*.txt")
 	if err != nil {

src/internal/testenv/testenv.go

@@ -286,3 +286,23 @@ func CleanCmdEnv(cmd *exec.Cmd) *exec.Cmd {
 	}
 	return cmd
 }
+
+// CPUIsSlow reports whether the CPU running the test is suspected to be slow.
+func CPUIsSlow() bool {
+	switch runtime.GOARCH {
+	case "arm", "mips", "mipsle", "mips64", "mips64le":
+		return true
+	}
+	return false
+}
+
+// SkipIfShortAndSlow skips t if -short is set and the CPU running the test is
+// suspected to be slow.
+//
+// (This is useful for CPU-intensive tests that otherwise complete quickly.)
+func SkipIfShortAndSlow(t testing.TB) {
+	if testing.Short() && CPUIsSlow() {
+		t.Helper()
+		t.Skipf("skipping test in -short mode on %s", runtime.GOARCH)
+	}
+}