cmd/nm: use the test binary as 'nm' instead of rebuilding it

This not only reduces the latency of the test, but also respects
build flags like '-race' and '-cover' passed to the 'go test' command.

Change-Id: Iffdc60d444a9ff1d4ff5e688bca1c2ef0dfa03c8
Reviewed-on: https://go-review.googlesource.com/c/go/+/450703
Run-TryBot: Bryan Mills <bcmills@google.com>
Auto-Submit: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>

src/cmd/nm/nm_test.go

@@ -5,53 +5,49 @@
 package main
 
 import (
-	"fmt"
 	"internal/obscuretestdata"
 	"internal/testenv"
 	"os"
-	"os/exec"
 	"path/filepath"
 	"runtime"
 	"strings"
+	"sync"
 	"testing"
 	"text/template"
 )
 
-var testnmpath string // path to nm command created for testing purposes
+// TestMain executes the test binary as the nm command if
-
+// GO_NMTEST_IS_NM is set, and runs the tests otherwise.
-// The TestMain function creates a nm command for testing purposes and
-// deletes it after the tests have been run.
 func TestMain(m *testing.M) {
-	os.Exit(testMain(m))
+	if os.Getenv("GO_NMTEST_IS_NM") != "" {
+		main()
+		os.Exit(0)
+	}
+
+	os.Setenv("GO_NMTEST_IS_NM", "1") // Set for subprocesses to inherit.
+	os.Exit(m.Run())
 }
 
-func testMain(m *testing.M) int {
+// nmPath returns the path to the "nm" binary to run.
-	if !testenv.HasGoBuild() {
+func nmPath(t testing.TB) string {
-		return 0
+	t.Helper()
-	}
+	testenv.MustHaveExec(t)
 
-	tmpDir, err := os.MkdirTemp("", "TestNM")
+	nmPathOnce.Do(func() {
-	if err != nil {
+		nmExePath, nmPathErr = os.Executable()
-		fmt.Println("TempDir failed:", err)
+	})
-		return 2
+	if nmPathErr != nil {
+		t.Fatal(nmPathErr)
 	}
-	defer os.RemoveAll(tmpDir)
+	return nmExePath
-
-	testnmpath = filepath.Join(tmpDir, "testnm.exe")
-	gotool, err := testenv.GoTool()
-	if err != nil {
-		fmt.Println("GoTool failed:", err)
-		return 2
-	}
-	out, err := exec.Command(gotool, "build", "-o", testnmpath, "cmd/nm").CombinedOutput()
-	if err != nil {
-		fmt.Printf("go build -o %v cmd/nm: %v\n%s", testnmpath, err, string(out))
-		return 2
-	}
-
-	return m.Run()
 }
 
+var (
+	nmPathOnce sync.Once
+	nmExePath  string
+	nmPathErr  error
+)
+
 func TestNonGoExecs(t *testing.T) {
 	t.Parallel()
 	testfiles := []string{
@@ -77,7 +73,7 @@ func TestNonGoExecs(t *testing.T) {
 			exepath = tf
 		}
 
-		cmd := exec.Command(testnmpath, exepath)
+		cmd := testenv.Command(t, nmPath(t), exepath)
 		out, err := cmd.CombinedOutput()
 		if err != nil {
 			t.Errorf("go tool nm %v: %v\n%s", exepath, err, string(out))
@@ -116,12 +112,12 @@ func testGoExec(t *testing.T, iscgo, isexternallinker bool) {
 		args = append(args, "-ldflags", "-linkmode="+linkmode)
 	}
 	args = append(args, src)
-	out, err := exec.Command(testenv.GoToolPath(t), args...).CombinedOutput()
+	out, err := testenv.Command(t, testenv.GoToolPath(t), args...).CombinedOutput()
 	if err != nil {
 		t.Fatalf("building test executable failed: %s %s", err, out)
 	}
 
-	out, err = exec.Command(exe).CombinedOutput()
+	out, err = testenv.Command(t, exe).CombinedOutput()
 	if err != nil {
 		t.Fatalf("running test executable failed: %s %s", err, out)
 	}
@@ -151,7 +147,7 @@ func testGoExec(t *testing.T, iscgo, isexternallinker bool) {
 		runtimeSyms["runtime.epclntab"] = "D"
 	}
 
-	out, err = exec.Command(testnmpath, exe).CombinedOutput()
+	out, err = testenv.Command(t, nmPath(t), exe).CombinedOutput()
 	if err != nil {
 		t.Fatalf("go tool nm: %v\n%s", err, string(out))
 	}
@@ -250,7 +246,7 @@ func testGoLib(t *testing.T, iscgo bool) {
 		t.Fatal(err)
 	}
 
-	cmd := exec.Command(testenv.GoToolPath(t), "build", "-buildmode=archive", "-o", "mylib.a", ".")
+	cmd := testenv.Command(t, testenv.GoToolPath(t), "build", "-buildmode=archive", "-o", "mylib.a", ".")
 	cmd.Dir = libpath
 	cmd.Env = append(os.Environ(), "GOPATH="+gopath)
 	out, err := cmd.CombinedOutput()
@@ -259,7 +255,7 @@ func testGoLib(t *testing.T, iscgo bool) {
 	}
 	mylib := filepath.Join(libpath, "mylib.a")
 
-	out, err = exec.Command(testnmpath, mylib).CombinedOutput()
+	out, err = testenv.Command(t, nmPath(t), mylib).CombinedOutput()
 	if err != nil {
 		t.Fatalf("go tool nm: %v\n%s", err, string(out))
 	}