[dev.fuzz] cmd/go: stream output when fuzzing

Previously, 'go test' streamed output when there were no package
arguments or when benchmarking. This CL expands that to include
fuzzing to ensure that coordinator progress messages are printed.

This change tweaks tests and output a little bit: the output is
slightly different depending on whether it was streamed or buffered in
'go test'.

Fixes golang/go#47603

Change-Id: I387470062cf0620f5c7f214b6f54039c921912c4
Reviewed-on: https://go-review.googlesource.com/c/go/+/344831
Trust: Jay Conrod <jayconrod@google.com>
Trust: Katie Hockman <katie@golang.org>
Run-TryBot: Jay Conrod <jayconrod@google.com>
Reviewed-by: Katie Hockman <katie@golang.org>

2 files changed, 33 insertions, 31 deletions

diff --git a/src/testing/fuzz.go b/src/testing/fuzz.go
index 6f5cdcc389..4892d3f3e9 100644
--- a/src/testing/fuzz.go
+++ b/src/testing/fuzz.go
@@ -561,12 +561,12 @@ func runFuzzTargets(deps testDeps, fuzzTargets []InternalFuzzTarget, deadline ti
 //
 // If fuzzing is disabled (-test.fuzz is not set), runFuzzing
 // returns immediately.
-func runFuzzing(deps testDeps, fuzzTargets []InternalFuzzTarget) (ran, ok bool) {
+func runFuzzing(deps testDeps, fuzzTargets []InternalFuzzTarget) (ran bool, matched int, ok bool) {
 	// TODO(katiehockman,jayconrod): Should we do something special to make sure
 	// we don't print f.Log statements again with runFuzzing, since we already
 	// would have printed them when we ran runFuzzTargets (ie. seed corpus run)?
 	if len(fuzzTargets) == 0 || *matchFuzz == "" {
-		return false, true
+		return false, 0, true
 	}
 	m := newMatcher(deps.MatchString, *matchFuzz, "-test.fuzz")
 	tctx := newTestContext(1, m)
@@ -588,41 +588,39 @@ func runFuzzing(deps testDeps, fuzzTargets []InternalFuzzTarget) (ran, ok bool)
 		root.chatty = newChattyPrinter(root.w)
 	}
 	var target *InternalFuzzTarget
-	var f *F
+	var targetName string
 	for i := range fuzzTargets {
-		ft := &fuzzTargets[i]
-		testName, matched, _ := tctx.match.fullName(nil, ft.Name)
-		if !matched {
+		name, ok, _ := tctx.match.fullName(nil, fuzzTargets[i].Name)
+		if !ok {
 			continue
 		}
-		if target != nil {
-			fmt.Fprintln(os.Stderr, "testing: warning: -fuzz matches more than one target, won't fuzz")
-			return false, true
-		}
-		target = ft
-		f = &F{
-			common: common{
-				signal:  make(chan bool),
-				barrier: nil, // T.Parallel has no effect when fuzzing.
-				name:    testName,
-				parent:  &root,
-				level:   root.level + 1,
-				chatty:  root.chatty,
-			},
-			fuzzContext: fctx,
-			testContext: tctx,
-		}
-		f.w = indenter{&f.common}
-	}
-	if target == nil {
-		return false, true
-	}
+		matched++
+		target = &fuzzTargets[i]
+		targetName = name
+	}
+	if matched != 1 {
+		return false, matched, true
+	}
+
+	f := &F{
+		common: common{
+			signal:  make(chan bool),
+			barrier: nil, // T.Parallel has no effect when fuzzing.
+			name:    targetName,
+			parent:  &root,
+			level:   root.level + 1,
+			chatty:  root.chatty,
+		},
+		fuzzContext: fctx,
+		testContext: tctx,
+	}
+	f.w = indenter{&f.common}
 	if f.chatty != nil {
 		f.chatty.Updatef(f.name, "=== FUZZ  %s\n", f.name)
 	}
 	go fRunner(f, target.Fn)
 	<-f.signal
-	return f.ran, !f.failed
+	return f.ran, matched, !f.failed
 }
 
 // fRunner wraps a call to a fuzz target and ensures that cleanup functions are
diff --git a/src/testing/testing.go b/src/testing/testing.go
index 4bf5685a07..7f78a7caf8 100644
--- a/src/testing/testing.go
+++ b/src/testing/testing.go
@@ -1618,9 +1618,13 @@ func (m *M) Run() (code int) {
 		}
 	}
 
-	fuzzingRan, fuzzingOk := runFuzzing(m.deps, m.fuzzTargets)
+	fuzzingRan, fuzzingMatched, fuzzingOk := runFuzzing(m.deps, m.fuzzTargets)
 	if *matchFuzz != "" && !fuzzingRan {
-		fmt.Fprintln(os.Stderr, "testing: warning: no targets to fuzz")
+		if fuzzingMatched == 0 {
+			fmt.Fprintln(os.Stderr, "testing: warning: no targets to fuzz")
+		} else {
+			fmt.Fprintln(os.Stderr, "testing: warning: will not fuzz, -fuzz matches more than one target")
+		}
 	}
 	if !*isFuzzWorker && !fuzzingOk {
 		fmt.Println("FAIL")