cmd/go: ignore stderr from tool version checks

There are multiple valid reasons a tool might print to stderr.
As long as we get the expected output on stdout, that's fine.

Fixes #22588.

Change-Id: I9c5d32da08288cb26dd575530a8257cd5f375367
Reviewed-on: https://go-review.googlesource.com/76017
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>

src/cmd/go/go_test.go

@@ -4740,6 +4740,21 @@ func TestBuildCache(t *testing.T) {
 	tg.grepStderr(`[\\/]link|gccgo`, "did not run linker")
 }
 
+func TestIssue22588(t *testing.T) {
+	// Don't get confused by stderr coming from tools.
+	tg := testgo(t)
+	defer tg.cleanup()
+	tg.parallel()
+
+	if _, err := os.Stat("/usr/bin/time"); err != nil {
+		t.Skip(err)
+	}
+
+	tg.run("list", "-f={{.Stale}}", "runtime")
+	tg.run("list", "-toolexec=/usr/bin/time", "-f={{.Stale}}", "runtime")
+	tg.grepStdout("false", "incorrectly reported runtime as stale")
+}
+
 func TestIssue22531(t *testing.T) {
 	if strings.Contains(os.Getenv("GODEBUG"), "gocacheverify") {
 		t.Skip("GODEBUG gocacheverify")

src/cmd/go/internal/work/buildid.go

@@ -5,6 +5,7 @@
 package work
 
 import (
+	"bytes"
 	"fmt"
 	"os"
 	"os/exec"
@@ -175,12 +176,14 @@ func (b *Builder) toolID(name string) string {
 	cmdline := str.StringList(cfg.BuildToolexec, base.Tool(name), "-V=full")
 	cmd := exec.Command(cmdline[0], cmdline[1:]...)
 	cmd.Env = base.EnvForDir(cmd.Dir, os.Environ())
-	out, err := cmd.CombinedOutput()
-	if err != nil {
-		base.Fatalf("go tool %s: %v\n%s", name, err, out)
+	var stdout, stderr bytes.Buffer
+	cmd.Stdout = &stdout
+	cmd.Stderr = &stderr
+	if err := cmd.Run(); err != nil {
+		base.Fatalf("go tool %s: %v\n%s%s", name, err, stdout.Bytes(), stderr.Bytes())
 	}
 
-	line := string(out)
+	line := stdout.String()
 	f := strings.Fields(line)
 	if len(f) < 3 || f[0] != name || f[1] != "version" || f[2] == "devel" && !strings.HasPrefix(f[len(f)-1], "buildID=") {
 		base.Fatalf("go tool %s -V=full: unexpected output:\n\t%s", name, line)