cmd/go: in TestScript, set GOTRACEBACK and use SIGQUIT to terminate hung subprocesses

This should produce more useful outputs if a cmd/go invocation hangs
during a test.

(In some cases the outputs will be very verbose, but verbose is still
better than uninformative.)

For #36460
For #38768

Change-Id: Ibaf2d0fbf7387dfab1aad8981140ecb11901fc4b
Reviewed-on: https://go-review.googlesource.com/c/go/+/308809
Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Jay Conrod <jayconrod@google.com>

src/cmd/go/script_test.go

@@ -172,6 +172,7 @@ func (ts *testScript) setup() {
 		"GOPRIVATE=",
 		"GOROOT=" + testGOROOT,
 		"GOROOT_FINAL=" + os.Getenv("GOROOT_FINAL"), // causes spurious rebuilds and breaks the "stale" built-in if not propagated
+		"GOTRACEBACK=all",
 		"TESTGO_GOROOT=" + testGOROOT,
 		"GOSUMDB=" + testSumDBVerifierKey,
 		"GONOPROXY=",
@@ -1120,24 +1121,12 @@ func (ts *testScript) startBackground(want simpleStatus, command string, args ..
 	}
 
 	go func() {
-		bg.err = waitOrStop(ts.ctx, cmd, stopSignal(), ts.gracePeriod)
+		bg.err = waitOrStop(ts.ctx, cmd, quitSignal(), ts.gracePeriod)
 		close(done)
 	}()
 	return bg, nil
 }
 
-// stopSignal returns the appropriate signal to use to request that a process
-// stop execution.
-func stopSignal() os.Signal {
-	if runtime.GOOS == "windows" {
-		// Per https://golang.org/pkg/os/#Signal, “Interrupt is not implemented on
-		// Windows; using it with os.Process.Signal will return an error.”
-		// Fall back to Kill instead.
-		return os.Kill
-	}
-	return os.Interrupt
-}
-
 // waitOrStop waits for the already-started command cmd by calling its Wait method.
 //
 // If cmd does not return before ctx is done, waitOrStop sends it the given interrupt signal.

src/cmd/go/stop_other_test.go

@@ -0,0 +1,33 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build !(aix || darwin || dragonfly || freebsd || (js && wasm) || linux || netbsd || openbsd || solaris)
+// +build !aix
+// +build !darwin
+// +build !dragonfly
+// +build !freebsd
+// +build !js !wasm
+// +build !linux
+// +build !netbsd
+// +build !openbsd
+// +build !solaris
+
+package main_test
+
+import (
+	"os"
+	"runtime"
+)
+
+// quitSignal returns the appropriate signal to use to request that a process
+// quit execution.
+func quitSignal() os.Signal {
+	if runtime.GOOS == "windows" {
+		// Per https://golang.org/pkg/os/#Signal, “Interrupt is not implemented on
+		// Windows; using it with os.Process.Signal will return an error.”
+		// Fall back to Kill instead.
+		return os.Kill
+	}
+	return os.Interrupt
+}

src/cmd/go/stop_unix_test.go

@@ -0,0 +1,17 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build aix || darwin || dragonfly || freebsd || (js && wasm) || linux || netbsd || openbsd || solaris
+// +build aix darwin dragonfly freebsd js,wasm linux netbsd openbsd solaris
+
+package main_test
+
+import (
+	"os"
+	"syscall"
+)
+
+func quitSignal() os.Signal {
+	return syscall.SIGQUIT
+}