cmd/go, testing: indicate when no tests are run

For example, testing the current directory:

	$ go test -run XXX
	testing: warning: no tests to run
	PASS
	ok  	testing	0.013s
	$

And in a summary:

	$ go test -run XXX testing
	ok  	testing	0.013s [no tests to run]
	$

These make it easy to spot when the -run regexp hasn't matched anything
or there are no tests. Previously the message was printed in the "current directory"
case when there were no tests at all, but not for no matches, and either way
was not surfaced in the directory list summary form.

Fixes #15211.

Change-Id: I1c82a423d6bd429fb991c9ca964c9d26c96fd3c5
Reviewed-on: https://go-review.googlesource.com/22341
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>

src/testing/testing.go

@@ -259,10 +259,12 @@ type common struct {
 	output   []byte       // Output generated by test or benchmark.
 	w        io.Writer    // For flushToParent.
 	chatty   bool         // A copy of the chatty flag.
+	ran      bool         // Test or benchmark (or one of its subtests) was executed.
 	failed   bool         // Test or benchmark has failed.
 	skipped  bool         // Test of benchmark has been skipped.
 	finished bool         // Test function has completed.
 	done     bool         // Test is finished and all subtests have completed.
+	hasSub   bool
 
 	parent   *common
 	level    int       // Nesting depth of test or benchmark.
@@ -410,6 +412,15 @@ func (c *common) Name() string {
 	return c.name
 }
 
+func (c *common) setRan() {
+	if c.parent != nil {
+		c.parent.setRan()
+	}
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	c.ran = true
+}
+
 // Fail marks the function as having failed but continues execution.
 func (c *common) Fail() {
 	if c.parent != nil {
@@ -616,6 +627,9 @@ func tRunner(t *T, fn func(t *T)) {
 		// Do not lock t.done to allow race detector to detect race in case
 		// the user does not appropriately synchronizes a goroutine.
 		t.done = true
+		if t.parent != nil && !t.hasSub {
+			t.setRan()
+		}
 		t.signal <- true
 	}()
 
@@ -627,6 +641,7 @@ func tRunner(t *T, fn func(t *T)) {
 // Run runs f as a subtest of t called name. It reports whether f succeeded.
 // Run will block until all its parallel subtests have completed.
 func (t *T) Run(name string, f func(t *T)) bool {
+	t.hasSub = true
 	testName, ok := t.context.match.fullName(&t.common, name)
 	if !ok {
 		return true
@@ -753,14 +768,17 @@ func (m *M) Run() int {
 	before()
 	startAlarm()
 	haveExamples = len(m.examples) > 0
-	testOk := RunTests(m.matchString, m.tests)
-	exampleOk := RunExamples(m.matchString, m.examples)
-	stopAlarm()
-	if !testOk || !exampleOk || !runBenchmarksInternal(m.matchString, m.benchmarks) {
+	testRan, testOk := runTests(m.matchString, m.tests)
+	exampleRan, exampleOk := runExamples(m.matchString, m.examples)
+	if !testRan && !exampleRan {
+		fmt.Fprintln(os.Stderr, "testing: warning: no tests to run")
+	}
+	if !testOk || !exampleOk || !runBenchmarks(m.matchString, m.benchmarks) {
 		fmt.Println("FAIL")
 		after()
 		return 1
 	}
+
 	fmt.Println("PASS")
 	after()
 	return 0
@@ -783,12 +801,18 @@ func (t *T) report() {
 	}
 }
 
+// An internal function but exported because it is cross-package; part of the implementation
+// of the "go test" command.
 func RunTests(matchString func(pat, str string) (bool, error), tests []InternalTest) (ok bool) {
-	ok = true
-	if len(tests) == 0 && !haveExamples {
+	ran, ok := runTests(matchString, tests)
+	if !ran && !haveExamples {
 		fmt.Fprintln(os.Stderr, "testing: warning: no tests to run")
-		return
 	}
+	return ok
+}
+
+func runTests(matchString func(pat, str string) (bool, error), tests []InternalTest) (ran, ok bool) {
+	ok = true
 	for _, procs := range cpuList {
 		runtime.GOMAXPROCS(procs)
 		ctx := newTestContext(*parallel, newMatcher(matchString, *match, "-test.run"))
@@ -811,8 +835,9 @@ func RunTests(matchString func(pat, str string) (bool, error), tests []InternalT
 			go func() { <-t.signal }()
 		})
 		ok = ok && !t.Failed()
+		ran = ran || t.ran
 	}
-	return
+	return ran, ok
 }
 
 // before runs before all testing.