cmd/go: in TestGoBuildUmask, create a file using os.WriteFile as a control

Fixes #62724.
Updates #17909.

Change-Id: Ib2e9abec4fb88f418c4251ece7fcdef315190835
Reviewed-on: https://go-review.googlesource.com/c/go/+/529495
Auto-Submit: Bryan Mills <bcmills@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>

diff --git a/src/cmd/go/go_unix_test.go b/src/cmd/go/go_unix_test.go
index d04e496778989b9fa757ddbdcb34e3a4008b95f6..a6b21b86d020994cc093102569c5d91b01ba8009 100644 (file)
--- a/src/cmd/go/go_unix_test.go
+++ b/src/cmd/go/go_unix_test.go
@@ -23,12 +23,27 @@ func TestGoBuildUmask(t *testing.T) {
        // Do not use tg.parallel; avoid other tests seeing umask manipulation.
        mask := syscall.Umask(0077) // prohibit low bits
        defer syscall.Umask(mask)
+
        tg := testgo(t)
        defer tg.cleanup()
        tg.tempFile("x.go", `package main; func main() {}`)
-       // Make sure artifact will be output to /tmp/... in case the user
-       // has POSIX acl's on their go source tree.
-       // See issue 17909.
+
+       // We have set a umask, but if the parent directory happens to have a default
+       // ACL, the umask may be ignored. To prevent spurious failures from an ACL,
+       // we compare the file created by "go build" against a file written explicitly
+       // by os.WriteFile.
+       //
+       // (See https://go.dev/issue/62724, https://go.dev/issue/17909.)
+       control := tg.path("control")
+       tg.creatingTemp(control)
+       if err := os.WriteFile(control, []byte("#!/bin/sh\nexit 0"), 0777); err != nil {
+               t.Fatal(err)
+       }
+       cfi, err := os.Stat(control)
+       if err != nil {
+               t.Fatal(err)
+       }
+
        exe := tg.path("x")
        tg.creatingTemp(exe)
        tg.run("build", "-o", exe, tg.path("x.go"))
@@ -36,8 +51,11 @@ func TestGoBuildUmask(t *testing.T) {
        if err != nil {
                t.Fatal(err)
        }
-       if mode := fi.Mode(); mode&0077 != 0 {
-               t.Fatalf("wrote x with mode=%v, wanted no 0077 bits", mode)
+       got, want := fi.Mode(), cfi.Mode()
+       if got == want {
+               t.Logf("wrote x with mode %v", got)
+       } else {
+               t.Fatalf("wrote x with mode %v, wanted no 0077 bits (%v)", got, want)
        }
 }