testing: fix panicking tests hang if Cleanup calls FailNow

Previously, it was impossible to call FailNow in a Cleanup.
Because it can terminate a panicking goroutine and cause its
parent hangs on t.signal channel. This CL sends the signal
in a deferred call to prevent the hang.

Fixes #41355

Change-Id: I4552d3a7ea763ef86817bf9b50c0e37fb34bf20f
Reviewed-on: https://go-review.googlesource.com/c/go/+/254637
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Emmanuel Odeke <emm.odeke@gmail.com>

src/cmd/go/testdata/script/test_cleanup_failnow.txt

@@ -0,0 +1,33 @@
+# For issue 41355
+[short] skip
+
+! go test -v cleanup_failnow/panic_nocleanup_test.go
+stdout '(?s)panic: die \[recovered\].*panic: die'
+! stdout '(?s)panic: die \[recovered\].*panic: die.*panic: die'
+
+! go test -v cleanup_failnow/panic_withcleanup_test.go
+stdout '(?s)panic: die \[recovered\].*panic: die'
+! stdout '(?s)panic: die \[recovered\].*panic: die.*panic: die'
+
+-- cleanup_failnow/panic_nocleanup_test.go --
+package panic_nocleanup_test
+import "testing"
+func TestX(t *testing.T) {
+	t.Run("x", func(t *testing.T) {
+		panic("die")
+	})
+}
+
+-- cleanup_failnow/panic_withcleanup_test.go --
+package panic_withcleanup_test
+import "testing"
+func TestCleanupWithFailNow(t *testing.T) {
+	t.Cleanup(func() {
+		t.FailNow()
+	})
+	t.Run("x", func(t *testing.T) {
+		t.Run("y", func(t *testing.T) {
+			panic("die")
+		})
+	})
+}

src/testing/testing.go

@@ -1075,6 +1075,7 @@ func tRunner(t *T, fn func(t *T)) {
 		// If the test panicked, print any test output before dying.
 		err := recover()
 		signal := true
+
 		if !t.finished && err == nil {
 			err = errNilPanicOrGoexit
 			for p := t.parent; p != nil; p = p.parent {
@@ -1086,6 +1087,15 @@ func tRunner(t *T, fn func(t *T)) {
 				}
 			}
 		}
+		// Use a deferred call to ensure that we report that the test is
+		// complete even if a cleanup function calls t.FailNow. See issue 41355.
+		didPanic := false
+		defer func() {
+			t.signal <- signal
+			if err != nil && !didPanic {
+				panic(err)
+			}
+		}()
 
 		doPanic := func(err interface{}) {
 			t.Fail()
@@ -1103,6 +1113,7 @@ func tRunner(t *T, fn func(t *T)) {
 					fmt.Fprintf(root.parent.w, "cleanup panicked with %v", r)
 				}
 			}
+			didPanic = true
 			panic(err)
 		}
 		if err != nil {
@@ -1144,7 +1155,6 @@ func tRunner(t *T, fn func(t *T)) {
 		if t.parent != nil && atomic.LoadInt32(&t.hasSub) == 0 {
 			t.setRan()
 		}
-		t.signal <- signal
 	}()
 	defer func() {
 		if len(t.sub) == 0 {