os: give race detector chance to override Exit(0)

Racy tests do not fail currently, they do os.Exit(0).
So if you run go test without -v, you won't even notice.
This was probably introduced with testing.TestMain.

Racy programs do not have the right to finish successfully.

Change-Id: Id133d7424f03d90d438bc3478528683dd02b8846
Reviewed-on: https://go-review.googlesource.com/4371
Reviewed-by: Russ Cox <rsc@golang.org>

src/os/proc.go

@@ -44,6 +44,14 @@ func Getgroups() ([]int, error) {
 
 // Exit causes the current program to exit with the given status code.
 // Conventionally, code zero indicates success, non-zero an error.
-// The program terminates immediately; deferred functions are
-// not run.
-func Exit(code int) { syscall.Exit(code) }
+// The program terminates immediately; deferred functions are not run.
+func Exit(code int) {
+	if code == 0 {
+		// Give race detector a chance to fail the program.
+		// Racy programs do not have the right to finish successfully.
+		runtime_beforeExit()
+	}
+	syscall.Exit(code)
+}
+
+func runtime_beforeExit() // implemented in runtime

src/runtime/proc.go

@@ -105,6 +105,14 @@ func main() {
 	}
 }
 
+// os_beforeExit is called from os.Exit(0).
+//go:linkname os_beforeExit os.runtime_beforeExit
+func os_beforeExit() {
+	if raceenabled {
+		racefini()
+	}
+}
+
 // start forcegc helper goroutine
 func init() {
 	go forcegchelper()

src/runtime/race/output_test.go

@@ -23,7 +23,11 @@ func TestOutput(t *testing.T) {
 			t.Fatalf("failed to create temp directory: %v", err)
 		}
 		defer os.RemoveAll(dir)
-		src := filepath.Join(dir, "main.go")
+		source := "main.go"
+		if test.run == "test" {
+			source = "main_test.go"
+		}
+		src := filepath.Join(dir, source)
 		f, err := os.Create(src)
 		if err != nil {
 			t.Fatalf("failed to create file: %v", err)
@@ -37,7 +41,7 @@ func TestOutput(t *testing.T) {
 			t.Fatalf("failed to close file: %v", err)
 		}
 		// Pass -l to the compiler to test stack traces.
-		cmd := exec.Command("go", "run", "-race", "-gcflags=-l", src)
+		cmd := exec.Command("go", test.run, "-race", "-gcflags=-l", src)
 		// GODEBUG spoils program output, GOMAXPROCS makes it flaky.
 		for _, env := range os.Environ() {
 			if strings.HasPrefix(env, "GODEBUG=") ||
@@ -58,11 +62,12 @@ func TestOutput(t *testing.T) {
 
 var tests = []struct {
 	name   string
+	run    string
 	gorace string
 	source string
 	re     string
 }{
-	{"simple", "atexit_sleep_ms=0", `
+	{"simple", "run", "atexit_sleep_ms=0", `
 package main
 import "time"
 func main() {
@@ -107,7 +112,7 @@ Found 1 data race\(s\)
 exit status 66
 `},
 
-	{"exitcode", "atexit_sleep_ms=0 exitcode=13", `
+	{"exitcode", "run", "atexit_sleep_ms=0 exitcode=13", `
 package main
 func main() {
 	done := make(chan bool)
@@ -121,7 +126,7 @@ func main() {
 }
 `, `exit status 13`},
 
-	{"strip_path_prefix", "atexit_sleep_ms=0 strip_path_prefix=/main.", `
+	{"strip_path_prefix", "run", "atexit_sleep_ms=0 strip_path_prefix=/main.", `
 package main
 func main() {
 	done := make(chan bool)
@@ -137,7 +142,7 @@ func main() {
       go:7 \+0x[0-9,a-f]+
 `},
 
-	{"halt_on_error", "atexit_sleep_ms=0 halt_on_error=1", `
+	{"halt_on_error", "run", "atexit_sleep_ms=0 halt_on_error=1", `
 package main
 func main() {
 	done := make(chan bool)
@@ -153,4 +158,23 @@ func main() {
 ==================
 exit status 66
 `},
+
+	{"test_fails_on_race", "test", "atexit_sleep_ms=0", `
+package main_test
+import "testing"
+func TestFail(t *testing.T) {
+	done := make(chan bool)
+	x := 0
+	go func() {
+		x = 42
+		done <- true
+	}()
+	x = 43
+	<-done
+}
+`, `
+==================
+PASS
+Found 1 data race\(s\)
+FAIL`},
 }