Quiet context.Canceled errors during shutdown

Runnable implementations that return ctx.Err() cause a spurious
"error received after stop" log message.

Author: cbandy

pkg/manager/internal.go

@@ -485,8 +485,8 @@ func (cm *controllerManager) engageStopProcedure(stopComplete <-chan struct{}) e
 				cm.internalCancel()
 			})
 			select {
-			case err, ok := <-cm.errChan:
-				if ok {
+			case err := <-cm.errChan:
+				if !errors.Is(err, context.Canceled) {
 					cm.logger.Error(err, "error received after stop sequence was engaged")
 				}
 			case <-stopComplete:

pkg/manager/manager_test.go

@@ -30,6 +30,7 @@ import (
 	"time"
 
 	"github.com/go-logr/logr"
+	"github.com/go-logr/logr/funcr"
 	. "github.com/onsi/ginkgo/v2"
 	. "github.com/onsi/gomega"
 	"github.com/prometheus/client_golang/prometheus"
@@ -1044,6 +1045,54 @@ var _ = Describe("manger.Manager", func() {
 				}))).NotTo(Succeed())
 			})
 
+			It("should not return runnables context.Canceled errors", func() {
+				Expect(options.Logger).To(BeZero(), "this test overrides Logger")
+
+				var log struct {
+					sync.Mutex
+					messages []string
+				}
+				options.Logger = funcr.NewJSON(func(object string) {
+					log.Lock()
+					log.messages = append(log.messages, object)
+					log.Unlock()
+				}, funcr.Options{})
+
+				m, err := New(cfg, options)
+				Expect(err).NotTo(HaveOccurred())
+				for _, cb := range callbacks {
+					cb(m)
+				}
+
+				// Runnables may return ctx.Err() as shown in some [context.Context] examples.
+				started := make(chan struct{})
+				Expect(m.Add(RunnableFunc(func(ctx context.Context) error {
+					close(started)
+					<-ctx.Done()
+					return ctx.Err()
+				}))).To(Succeed())
+
+				stopped := make(chan error)
+				ctx, cancel := context.WithCancel(context.Background())
+				go func() {
+					stopped <- m.Start(ctx)
+				}()
+
+				// Wait for runnables to start, signal the manager, and wait for it.
+				<-started
+				cancel()
+				Expect(<-stopped).To(Succeed())
+
+				// TODO: Diagnose why LeaderElection races after Start() returns.
+				if options.LeaderElection {
+					time.Sleep(time.Second)
+				}
+
+				Expect(log.messages).To(Not(ContainElement(
+					ContainSubstring(context.Canceled.Error()),
+				)))
+			})
+
 			It("should return both runnables and stop errors when both error", func() {
 				m, err := New(cfg, options)
 				Expect(err).NotTo(HaveOccurred())