Use errors.As and errors.Is for safe checks and casts

pkg/errors/factory.go

@@ -15,6 +15,7 @@
 package errors
 
 import (
+	"errors"
 	"net/http"
 	"strings"
 
@@ -52,17 +53,17 @@ func GetError(err error) error {
 	case isNoRouteToHostError(err):
 		return newNoRouteToHost(err.Error())
 	default:
-		apiStatus, ok := err.(api_errors.APIStatus)
-		if !ok {
+		var errAPIStatus api_errors.APIStatus
+		if !errors.As(err, &errAPIStatus) {
 			return err
 		}
-		if apiStatus.Status().Details == nil {
+		if errAPIStatus.Status().Details == nil {
 			return err
 		}
 		var knerr *KNError
-		if isCRDError(apiStatus) {
-			knerr = newInvalidCRD(apiStatus.Status().Details.Group)
-			knerr.Status = apiStatus
+		if isCRDError(errAPIStatus) {
+			knerr = newInvalidCRD(errAPIStatus.Status().Details.Group)
+			knerr.Status = errAPIStatus
 			return knerr
 		}
 		return err
@@ -71,8 +72,9 @@ func GetError(err error) error {
 
 // IsForbiddenError returns true if given error can be converted to API status and of type forbidden access else false
 func IsForbiddenError(err error) bool {
-	if status, ok := err.(api_errors.APIStatus); ok {
-		return status.Status().Code == int32(http.StatusForbidden)
+	var errAPIStatus api_errors.APIStatus
+	if !errors.As(err, &errAPIStatus) {
+		return false
 	}
-	return false
+	return errAPIStatus.Status().Code == int32(http.StatusForbidden)
 }

pkg/kn/commands/service/update.go

@@ -87,7 +87,8 @@ func NewServiceUpdateCommand(p *commands.KnParams) *cobra.Command {
 				var baseRevision *servingv1.Revision
 				if !cmd.Flags().Changed("image") && editFlags.LockToDigest {
 					baseRevision, err = client.GetBaseRevision(service)
-					if _, ok := err.(*clientservingv1.NoBaseRevisionError); ok {
+					var errNoBaseRevision clientservingv1.NoBaseRevisionError
+					if errors.As(err, &errNoBaseRevision) {
 						fmt.Fprintf(cmd.OutOrStdout(), "Warning: No revision found to update image digest")
 					}
 				}

pkg/kn/config/config.go

@@ -15,6 +15,7 @@
 package config
 
 import (
+	"errors"
 	"fmt"
 	"os"
 	"path/filepath"
@@ -106,7 +107,7 @@ func BootstrapConfig() error {
 	bootstrapFlagSet.ParseErrorsWhitelist = flag.ParseErrorsWhitelist{UnknownFlags: true} // wokeignore:rule=whitelist // TODO(#1031)
 	bootstrapFlagSet.Usage = func() {}
 	err := bootstrapFlagSet.Parse(os.Args)
-	if err != nil && err != flag.ErrHelp {
+	if err != nil && !errors.Is(err, flag.ErrHelp) {
 		return err
 	}
 

pkg/kn/plugin/manager.go

@@ -15,6 +15,7 @@
 package plugin
 
 import (
+	"errors"
 	"fmt"
 	"io/ioutil"
 	"os"
@@ -449,7 +450,7 @@ func findInDirOrPath(name string, dir string, lookupInPath bool) (string, error)
 				// Found in path
 				return path, nil
 			}
-			if execErr, ok := err.(*exec.Error); !ok || execErr.Unwrap() != exec.ErrNotFound {
+			if errors.Is(err, exec.ErrNotFound) {
 				return "", fmt.Errorf("error for looking up %s in path: %w", name, err)
 			}
 		}

pkg/kn/plugin/verify.go

@@ -15,6 +15,7 @@
 package plugin
 
 import (
+	"errors"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -83,7 +84,7 @@ func verifyPath(path string, seenPlugins map[string]string, eaw VerificationErro
 	// Verify that plugin actually exists
 	fileInfo, err := os.Stat(path)
 	if err != nil {
-		if err == os.ErrNotExist {
+		if errors.Is(err, os.ErrNotExist) {
 			return eaw.AddError("cannot find plugin in %s", path)
 		}
 		return eaw.AddError("cannot stat %s: %v", path, err)