os/exec: simplify Windows-specific tests

- Use the test binary itself for printing paths instead of building a
  separate binary and running it through additional subprocesses.

- Factor out a common chdir helper.

- Use t.Setenv where appropriate.

- Reduce indirection in test helpers.

- Set NoDefaultCurrentDirectoryInExePath consistently in the
  environment.

Also add a test case demonstrating an interesting behavior for
relative paths that may interact with #62596.

Fixes #62594.
For #62596.

Change-Id: I19b9325034edf78cd0ca747594476cd7432bb451
Reviewed-on: https://go-review.googlesource.com/c/go/+/528035
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Bryan Mills <bcmills@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

1 files changed, 37 insertions, 0 deletions

diff --git a/src/os/exec/exec_test.go b/src/os/exec/exec_test.go
index 473f92ba8e..9783a133ba 100644
--- a/src/os/exec/exec_test.go
+++ b/src/os/exec/exec_test.go
@@ -77,6 +77,21 @@ func TestMain(m *testing.M) {
 	if os.Getenv("GO_EXEC_TEST_PID") == "" {
 		os.Setenv("GO_EXEC_TEST_PID", strconv.Itoa(pid))
 
+		if runtime.GOOS == "windows" {
+			// Normalize environment so that test behavior is consistent.
+			// (The behavior of LookPath varies depending on this variable.)
+			//
+			// Ideally we would test both with the variable set and with it cleared,
+			// but I (bcmills) am not sure that that's feasible: it may already be set
+			// in the Windows registry, and I'm not sure if it is possible to remove
+			// a registry variable in a program's environment.
+			//
+			// Per https://learn.microsoft.com/en-us/windows/win32/api/processenv/nf-processenv-needcurrentdirectoryforexepathw#remarks,
+			// “the existence of the NoDefaultCurrentDirectoryInExePath environment
+			// variable is checked, and not its value.”
+			os.Setenv("NoDefaultCurrentDirectoryInExePath", "TRUE")
+		}
+
 		code := m.Run()
 		if code == 0 && flag.Lookup("test.run").Value.String() == "" && flag.Lookup("test.list").Value.String() == "" {
 			for cmd := range helperCommands {
@@ -180,6 +195,28 @@ var exeOnce struct {
 	sync.Once
 }
 
+func chdir(t *testing.T, dir string) {
+	t.Helper()
+
+	prev, err := os.Getwd()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := os.Chdir(dir); err != nil {
+		t.Fatal(err)
+	}
+	t.Logf("Chdir(%#q)", dir)
+
+	t.Cleanup(func() {
+		if err := os.Chdir(prev); err != nil {
+			// Couldn't chdir back to the original working directory.
+			// panic instead of t.Fatal so that we don't run other tests
+			// in an unexpected location.
+			panic("couldn't restore working directory: " + err.Error())
+		}
+	})
+}
+
 var helperCommandUsed sync.Map
 
 var helperCommands = map[string]func(...string){