linter: enable nilerr

A number of cases looked suspicious, so I marked them with `FIXME`s to
leave some breadcrumbs.

Signed-off-by: Valentin Rothberg <vrothberg@redhat.com>

.golangci.yml

@@ -62,7 +62,6 @@ linters:
     - ireturn
     - varnamelen
     - maintidx
-    - nilerr
     - nilnil
 linters-settings:
   errcheck:

cmd/podman/containers/cp.go

@@ -449,7 +449,7 @@ func resolvePathOnDestinationContainer(container string, containerPath string, i
 	containerInfo, err = registry.ContainerEngine().ContainerStat(registry.GetContext(), container, containerPath)
 	if err == nil {
 		baseName = filepath.Base(containerInfo.LinkTarget)
-		return
+		return // nolint: nilerr
 	}
 
 	if strings.HasSuffix(containerPath, "/") {

cmd/podman/images/scp.go

@@ -264,7 +264,7 @@ func saveToRemote(image, localFile string, tag string, uri *urlP.URL, iden strin
 	run := podman + " image save " + image + " --format=oci-archive --output=" + remoteFile // run ssh image load of the file copied via scp. Files are reverse in this case...
 	_, err = connection.ExecRemoteCommand(dial, run)
 	if err != nil {
-		return nil
+		return err
 	}
 	n, err := scpD.CopyFrom(dial, remoteFile, localFile)
 	connection.ExecRemoteCommand(dial, "rm "+remoteFile)

cmd/podman/system/df.go

@@ -171,7 +171,7 @@ func printVerbose(cmd *cobra.Command, reports *entities.SystemDfReport) error {
 		return err
 	}
 	if err := writeTemplate(rpt, hdrs, dfImages); err != nil {
-		return nil
+		return err
 	}
 
 	fmt.Fprint(rpt.Writer(), "\nContainers space usage:\n\n")
@@ -191,7 +191,7 @@ func printVerbose(cmd *cobra.Command, reports *entities.SystemDfReport) error {
 		return err
 	}
 	if err := writeTemplate(rpt, hdrs, dfContainers); err != nil {
-		return nil
+		return err
 	}
 
 	fmt.Fprint(rpt.Writer(), "\nLocal Volumes space usage:\n\n")

libpod/boltdb_state.go

@@ -366,7 +366,8 @@ func (s *BoltState) GetDBConfig() (*DBConfig, error) {
 	err = db.View(func(tx *bolt.Tx) error {
 		configBucket, err := getRuntimeConfigBucket(tx)
 		if err != nil {
-			return nil
+			// FIXME: this error should probably be returned
+			return nil // nolint: nilerr
 		}
 
 		// Some of these may be nil

libpod/container_internal_linux.go

@@ -2587,7 +2587,7 @@ func (c *Container) generateUserGroupEntry(addedGID int) (string, int, error) {
 
 	gid, err := strconv.ParseUint(group, 10, 32)
 	if err != nil {
-		return "", 0, nil
+		return "", 0, nil // nolint: nilerr
 	}
 
 	if addedGID != 0 && addedGID == int(gid) {
@@ -2740,7 +2740,8 @@ func (c *Container) generateUserPasswdEntry(addedUID int) (string, int, int, err
 	// If a non numeric User, then don't generate passwd
 	uid, err := strconv.ParseUint(userspec, 10, 32)
 	if err != nil {
-		return "", 0, 0, nil
+		// FIXME: this error should probably be returned
+		return "", 0, 0, nil // nolint: nilerr
 	}
 
 	if addedUID != 0 && int(uid) == addedUID {

libpod/oci_conmon_linux.go

@@ -750,7 +750,7 @@ func openControlFile(ctr *Container, parentDir string) (*os.File, error) {
 	for i := 0; i < 600; i++ {
 		controlFile, err := os.OpenFile(controlPath, unix.O_WRONLY|unix.O_NONBLOCK, 0)
 		if err == nil {
-			return controlFile, err
+			return controlFile, nil
 		}
 		if !isRetryable(err) {
 			return nil, errors.Wrapf(err, "could not open ctl file for terminal resize for container %s", ctr.ID())
@@ -1015,7 +1015,8 @@ func (r *ConmonOCIRuntime) getLogTag(ctr *Container) (string, error) {
 	}
 	data, err := ctr.inspectLocked(false)
 	if err != nil {
-		return "", nil
+		// FIXME: this error should probably be returned
+		return "", nil // nolint: nilerr
 	}
 	tmpl, err := template.New("container").Parse(logTag)
 	if err != nil {

pkg/api/handlers/utils/images.go

@@ -63,7 +63,7 @@ func IsRegistryReference(name string) error {
 	imageRef, err := alltransports.ParseImageName(name)
 	if err != nil {
 		// No supported transport -> assume a docker-stype reference.
-		return nil
+		return nil // nolint: nilerr
 	}
 	if imageRef.Transport().Name() == docker.Transport.Name() {
 		return nil

pkg/bindings/containers/attach.go

@@ -279,7 +279,7 @@ func DemuxFrame(r io.Reader, buffer []byte, length int) (frame []byte, err error
 
 	n, err := io.ReadFull(r, buffer[0:length])
 	if err != nil {
-		return nil, nil
+		return nil, err
 	}
 	if n < length {
 		err = io.ErrUnexpectedEOF

pkg/bindings/test/common_test.go

@@ -211,7 +211,7 @@ func (b *bindingTest) RunTopContainer(containerName *string, podName *string) (s
 	}
 	ctr, err := containers.CreateWithSpec(b.conn, s, nil)
 	if err != nil {
-		return "", nil
+		return "", err
 	}
 	err = containers.Start(b.conn, ctr.ID, nil)
 	if err != nil {

pkg/checkpoint/crutils/checkpoint_restore_utils.go

@@ -99,13 +99,12 @@ func CRRemoveDeletedFiles(id, baseDirectory, containerRootDirectory string) erro
 // root file system changes on top of containerRootDirectory
 func CRApplyRootFsDiffTar(baseDirectory, containerRootDirectory string) error {
 	rootfsDiffPath := filepath.Join(baseDirectory, metadata.RootFsDiffTar)
-	if _, err := os.Stat(rootfsDiffPath); err != nil {
+	// Only do this if a rootfs-diff.tar actually exists
-		// Only do this if a rootfs-diff.tar actually exists
-		return nil
-	}
-
 	rootfsDiffFile, err := os.Open(rootfsDiffPath)
 	if err != nil {
+		if os.IsNotExist(err) {
+			return nil
+		}
 		return errors.Wrap(err, "failed to open root file-system diff file")
 	}
 	defer rootfsDiffFile.Close()

pkg/domain/filters/containers.go

@@ -213,8 +213,10 @@ func GenerateContainerFilterFuncs(filter string, filterValues []string, r *libpo
 		for _, val := range filterValues {
 			net, err := r.Network().NetworkInspect(val)
 			if err != nil {
-				// ignore not found errors
+				if errors.Cause(err) == define.ErrNoSuchNetwork {
-				break
+					continue
+				}
+				return nil, err
 			}
 			inputNetNames = append(inputNetNames, net.Name)
 		}

pkg/domain/filters/pods.go

@@ -131,8 +131,10 @@ func GeneratePodFilterFunc(filter string, filterValues []string, r *libpod.Runti
 		for _, val := range filterValues {
 			net, err := r.Network().NetworkInspect(val)
 			if err != nil {
-				// ignore not found errors
+				if errors.Cause(err) == define.ErrNoSuchNetwork {
-				break
+					continue
+				}
+				return nil, err
 			}
 			inputNetNames = append(inputNetNames, net.Name)
 		}

pkg/domain/infra/abi/volumes.go

@@ -171,7 +171,8 @@ func (ic *ContainerEngine) VolumeMounted(ctx context.Context, nameOrID string) (
 	}
 	mountCount, err := vol.MountCount()
 	if err != nil {
-		return &entities.BoolReport{Value: false}, nil
+		// FIXME: this error should probably be returned
+		return &entities.BoolReport{Value: false}, nil // nolint: nilerr
 	}
 	if mountCount > 0 {
 		return &entities.BoolReport{Value: true}, nil

pkg/domain/infra/tunnel/containers.go

@@ -840,7 +840,7 @@ func (ic *ContainerEngine) ContainerRun(ctx context.Context, opts entities.Conta
 	if eventsErr != nil || lastEvent == nil {
 		logrus.Errorf("Cannot get exit code: %v", err)
 		report.ExitCode = define.ExecErrorCodeNotFound
-		return &report, nil // compat with local client
+		return &report, nil // nolint: nilerr
 	}
 
 	report.ExitCode = lastEvent.ContainerExitCode

pkg/errorhandling/errorhandling.go

@@ -28,7 +28,7 @@ func JoinErrors(errs []error) error {
 
 	finalErr := multiE.ErrorOrNil()
 	if finalErr == nil {
-		return finalErr
+		return nil
 	}
 	return errors.New(strings.TrimSpace(finalErr.Error()))
 }

pkg/machine/fedora.go

@@ -59,7 +59,10 @@ func (f FedoraDownload) Get() *Download {
 func (f FedoraDownload) HasUsableCache() (bool, error) {
 	info, err := os.Stat(f.LocalPath)
 	if err != nil {
-		return false, nil
+		if os.IsNotExist(err) {
+			return false, nil
+		}
+		return false, err
 	}
 	return info.Size() == f.Size, nil
 }

pkg/machine/qemu/machine.go

@@ -626,7 +626,8 @@ func (v *MachineVM) Stop(name string, _ machine.StopOptions) error {
 	}
 
 	if err := qmpMonitor.Disconnect(); err != nil {
-		return nil
+		// FIXME: this error should probably be returned
+		return nil // nolint: nilerr
 	}
 
 	disconnected = true
@@ -755,7 +756,8 @@ func (v *MachineVM) isRunning() (bool, error) {
 	// Check if we can dial it
 	monitor, err := qmp.NewSocketMonitor(v.QMPMonitor.Network, v.QMPMonitor.Address, v.QMPMonitor.Timeout)
 	if err != nil {
-		return false, nil
+		// FIXME: this error should probably be returned
+		return false, nil // nolint: nilerr
 	}
 	if err := monitor.Connect(); err != nil {
 		return false, err

pkg/rootless/rootless.go

@@ -16,12 +16,15 @@ import (
 // file.
 func TryJoinPauseProcess(pausePidPath string) (bool, int, error) {
 	if _, err := os.Stat(pausePidPath); err != nil {
-		return false, -1, nil
+		if os.IsNotExist(err) {
+			return false, -1, nil
+		}
+		return false, -1, err
 	}
 
 	became, ret, err := TryJoinFromFilePaths("", false, []string{pausePidPath})
 	if err == nil {
-		return became, ret, err
+		return became, ret, nil
 	}
 
 	// It could not join the pause process, let's lock the file before trying to delete it.
@@ -46,7 +49,7 @@ func TryJoinPauseProcess(pausePidPath string) (bool, int, error) {
 	if err != nil {
 		// It is still failing.  We can safely remove it.
 		os.Remove(pausePidPath)
-		return false, -1, nil
+		return false, -1, nil // nolint: nilerr
 	}
 	return became, ret, err
 }

pkg/util/utils.go

@@ -727,7 +727,7 @@ func SocketPath() (string, error) {
 func LookupUser(name string) (*user.User, error) {
 	// Assume UID look up first, if it fails lookup by username
 	if u, err := user.LookupId(name); err == nil {
-		return u, err
+		return u, nil
 	}
 	return user.Lookup(name)
 }

test/utils/matchers.go

@@ -184,7 +184,7 @@ func (matcher *ValidJSONMatcher) Match(actual interface{}) (success bool, err er
 
 	var i interface{}
 	if err := json.Unmarshal([]byte(s), &i); err != nil {
-		return false, nil
+		return false, err
 	}
 	return true, nil
 }