cmd/go: honor -timeout=0 to mean no timeout

The test binaries accept -timeout=0 to mean no timeout,
but then the backup timer in cmd/go kills the test after 1 minute.
Make cmd/go understand this special case and change
behavior accordingly.

Fixes #14780.

Change-Id: I66bf517173a4ad21d53a5ee88d163f04b8929fb6
Reviewed-on: https://go-review.googlesource.com/81499
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/go/alldocs.go

@@ -1199,9 +1199,9 @@
 // 	GO386
 // 		For GOARCH=386, the floating point instruction set.
 // 		Valid values are 387, sse2.
-//	GOMIPS
-//		For GOARCH=mips{,le}, whether to use floating point instructions.
-//		Valid values are hardfloat (default), softfloat.
+// 	GOMIPS
+// 		For GOARCH=mips{,le}, whether to use floating point instructions.
+// 		Valid values are hardfloat (default), softfloat.
 //
 // Special-purpose environment variables:
 //
@@ -1575,6 +1575,7 @@
 //
 // 	-timeout d
 // 	    If a test binary runs longer than duration d, panic.
+// 	    If d is 0, the timeout is disabled.
 // 	    The default is 10 minutes (10m).
 //
 // 	-v

src/cmd/go/internal/test/test.go

@@ -272,6 +272,7 @@ const testFlag2 = `
 
 	-timeout d
 	    If a test binary runs longer than duration d, panic.
+	    If d is 0, the timeout is disabled.
 	    The default is 10 minutes (10m).
 
 	-v
@@ -549,6 +550,10 @@ func runTest(cmd *base.Command, args []string) {
 	// timer does not get a chance to fire.
 	if dt, err := time.ParseDuration(testTimeout); err == nil && dt > 0 {
 		testKillTimeout = dt + 1*time.Minute
+	} else if err == nil && dt == 0 {
+		// An explicit zero disables the test timeout.
+		// Let it have one century (almost) before we kill it.
+		testKillTimeout = 100 * 365 * 24 * time.Hour
 	}
 
 	// show passing test output (after buffering) with -v flag.

src/testing/testing.go

@@ -265,7 +265,7 @@ var (
 	mutexProfile         = flag.String("test.mutexprofile", "", "write a mutex contention profile to the named file after execution")
 	mutexProfileFraction = flag.Int("test.mutexprofilefraction", 1, "if >= 0, calls runtime.SetMutexProfileFraction()")
 	traceFile            = flag.String("test.trace", "", "write an execution trace to `file`")
-	timeout              = flag.Duration("test.timeout", 0, "panic test binary after duration `d` (0 means unlimited)")
+	timeout              = flag.Duration("test.timeout", 0, "panic test binary after duration `d` (default 0, timeout disabled)")
 	cpuListStr           = flag.String("test.cpu", "", "comma-separated `list` of cpu counts to run each test with")
 	parallel             = flag.Int("test.parallel", runtime.GOMAXPROCS(0), "run at most `n` tests in parallel")