test(project): start the waitdelay deadline once the grandchild holds the pipe

internal/project/waitdelay_test.go

@@ -12,13 +12,15 @@ import (
 // helperEnv selects which half of the process tree a helper run plays.
 const helperEnv = "LICH_WAITDELAY_HELPER"
 
-// releaseEnv names the directory the grandchild watches: the test writes
+// releaseEnv names the directory the grandchild and the test signal each other
+// in: the grandchild writes holdingFile once it holds the pipe, the test writes
 // releaseFile there once it is done with the grandchild, which then exits and
 // writes exitedFile. Left to sleep out its hold, the grandchild outlived a
 // package that finished sooner, still running the test binary go test was
 // deleting: "unlinkat ... project.test.exe: Access is denied" on Windows.
 const (
 	releaseEnv  = "LICH_WAITDELAY_RELEASE"
+	holdingFile = "holding"
 	releaseFile = "release"
 	exitedFile  = "exited"
 )
@@ -50,6 +52,9 @@ func TestSubprocessHelper(t *testing.T) {
 		os.Exit(0)
 	case "grandchild":
 		dir := os.Getenv(releaseEnv)
+		if err := os.WriteFile(filepath.Join(dir, holdingFile), nil, 0o644); err != nil {
+			os.Exit(1)
+		}
 		awaitFile(filepath.Join(dir, releaseFile), grandchildHold)
 		if err := os.WriteFile(filepath.Join(dir, exitedFile), nil, 0o644); err != nil {
 			os.Exit(1)
@@ -72,6 +77,11 @@ func awaitFile(path string, limit time.Duration) bool {
 // here exits immediately and the grandchild behind it keeps stdout open until
 // released: with nothing closing that pipe, Output waits for it and reports
 // success, deadline or none.
+//
+// The deadline is the moment the grandchild holds the pipe, not a timer: a
+// fixed 200ms ran out on Windows before the test binary had started twice, the
+// context killed the child before it spawned the grandchild, and the cleanup
+// waited ten seconds for a grandchild that never existed.
 func TestSubprocessBudgetOutlivesAGrandchild(t *testing.T) {
 	t.Parallel()
 	dir := t.TempDir()
@@ -83,16 +93,30 @@ func TestSubprocessBudgetOutlivesAGrandchild(t *testing.T) {
 			t.Fatal("the grandchild did not exit once released")
 		}
 	})
-	ctx, cancel := context.WithTimeout(context.Background(), 200*time.Millisecond)
+	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
 	cmd := commandContext(ctx, os.Args[0], "-test.run=TestSubprocessHelper")
 	cmd.Env = append(cmd.Env, helperEnv+"=child", releaseEnv+"="+dir)
 
-	start := time.Now()
+	type deadline struct {
+		held bool
+		at   time.Time
+	}
+	reached := make(chan deadline, 1)
+	go func() {
+		held := awaitFile(filepath.Join(dir, holdingFile), grandchildHold)
+		cancel()
+		reached <- deadline{held: held, at: time.Now()}
+	}()
+
 	_, err := cmd.Output()
-	elapsed := time.Since(start)
+	returned := time.Now()
+	d := <-reached
 
-	if elapsed > 5*time.Second {
-		t.Fatalf("Output blocked %s on a grandchild holding the pipe, err %v: the 200ms budget bounded the child alone", elapsed, err)
+	if !d.held {
+		t.Fatalf("the grandchild never held the pipe within %s, Output err %v", grandchildHold, err)
+	}
+	if elapsed := returned.Sub(d.at); elapsed > 5*time.Second {
+		t.Fatalf("Output blocked %s past the deadline on a grandchild holding the pipe, err %v: the budget bounded the child alone", elapsed, err)
 	}
 }