🔀 Merge branch 'errgatherer-onfail' into 'dev'

[pkg/errors] Add Gatherer.OnFail hooks

See merge request perun/go-perun!395

Signed-off-by: Steffen Rattay <steffen@perun.network>

Author: RmbRT

pkg/errors/gatherer.go

@@ -35,7 +35,8 @@ type Gatherer struct {
 	errs  accumulatedError
 	wg    sync.WaitGroup
 
-	failed chan struct{} // Closed when an error has occurred.
+	onFails []func()
+	failed  chan struct{} // Closed when an error has occurred.
 }
 
 // Failed returns a channel that is closed when an error occurs.
@@ -56,8 +57,14 @@ func (g *Gatherer) Add(err error) {
 
 	select {
 	case <-g.failed:
+		return
 	default:
-		close(g.failed)
+	}
+
+	close(g.failed)
+
+	for _, fn := range g.onFails {
+		fn()
 	}
 }
 
@@ -87,6 +94,15 @@ func (g *Gatherer) Err() error {
 	return g.errs
 }
 
+// OnFail adds fn to the list of functions that are executed right after any
+// non-nil error is added with Add (or any routine started with Go failed). The
+// functions are guaranteed to be executed in the order that they were added.
+//
+// The channel returned by Failed is closed before those functions are executed.
+func (g *Gatherer) OnFail(fn func()) {
+	g.onFails = append(g.onFails, fn)
+}
+
 // stackTracer is taken from the github.com/pkg/errors documentation.
 type stackTracer interface {
 	StackTrace() errors.StackTrace

pkg/errors/gatherer_test.go

@@ -112,3 +112,36 @@ func TestAccumulatedError_StackTrace(t *testing.T) {
 	g.Add(pkgerrors.New("2"))
 	assert.NotNil(t, g.Err().(stackTracer).StackTrace())
 }
+
+func TestGatherer_OnFail(t *testing.T) {
+	var (
+		assert  = assert.New(t)
+		g       = errors.NewGatherer()
+		called  bool
+		called2 bool
+	)
+
+	g.OnFail(func() {
+		select {
+		case <-g.Failed():
+		case <-time.After(time.Second):
+			assert.Fail("Failed not closed before OnFail hooks are executed")
+		}
+
+		called = true
+		assert.False(called2)
+	})
+
+	g.OnFail(func() {
+		assert.True(called)
+		called2 = true
+	})
+
+	g.Add(nil)
+	assert.False(called)
+	assert.False(called2)
+
+	g.Add(stderrors.New("error"))
+	assert.True(called)
+	assert.True(called2)
+}