✨ Short-circuit new goroutines if an error already occured

errgroup_test.go

@@ -98,6 +98,38 @@ func ExampleGroup_parallel() {
 	// video result for "golang"
 }
 
+// FirstError demonstrates that g.Go becomes a no-op if a previous g.Go
+// has returned an error.
+func ExampleGroup_firstError() {
+	err1 := errors.New("errgroup_test: 1")
+	err2 := errors.New("errgroup_test: 2")
+
+	g := new(errgroup.Group)
+
+	ch := make(chan struct{})
+
+	g.Go(func() error {
+		fmt.Printf("Returning %s\n", err1)
+		ch <- struct{}{}
+		return err1
+	})
+
+	<-ch
+
+	g.Go(func() error {
+		// This should never run
+		fmt.Printf("Returning %s\n", err2)
+		return err2
+	})
+
+	err := g.Wait()
+	fmt.Printf("Got %s\n", err)
+
+	// Output:
+	// Returning errgroup_test: 1
+	// Got errgroup_test: 1
+}
+
 func TestZeroGroup(t *testing.T) {
 	err1 := errors.New("errgroup_test: 1")
 	err2 := errors.New("errgroup_test: 2")
@@ -256,6 +288,7 @@ func TestCancelCause(t *testing.T) {
 		{errs: []error{nil}, want: nil},
 		{errs: []error{errDoom}, want: errDoom},
 		{errs: []error{errDoom, nil}, want: errDoom},
+		{errs: []error{nil, errDoom}, want: errDoom},
 	}
 
 	for _, tc := range cases {