Disallow fmt.Errorf usage through code validation (#433)

Came across during a code review, new contributors can end up using fmt.Errorf
which does not create stack trace at the error site --and also doesn't preserve
stack trace if used to wrap an error.

Signed-off-by: Ahmet Alp Balkan <[email protected]>

cmd/krew/cmd/root.go

@@ -94,7 +94,7 @@ func preRun(cmd *cobra.Command, _ []string) error {
 	}
 	if !isMigrated && cmd.Use != "receipts-upgrade" {
 		fmt.Fprintln(os.Stderr, "You need to perform a migration to continue using krew.\nPlease run `kubectl krew system receipts-upgrade`")
-		return fmt.Errorf("krew home outdated")
+		return errors.New("krew home outdated")
 	}
 
 	if installation.IsWindows() {

cmd/validate-krew-manifest/main.go

@@ -70,7 +70,7 @@ func validateManifestFile(path string) error {
 	filename := filepath.Base(path)
 	manifestExtension := filepath.Ext(filename)
 	if manifestExtension != constants.ManifestExtension {
-		return fmt.Errorf("expected manifest extension %q but found %q", constants.ManifestExtension, manifestExtension)
+		return errors.Errorf("expected manifest extension %q but found %q", constants.ManifestExtension, manifestExtension)
 	}
 	pluginNameFromFileName := strings.TrimSuffix(filename, manifestExtension)
 	klog.V(4).Infof("inferred plugin name as %s", pluginNameFromFileName)

hack/verify-code-patterns.sh

@@ -44,6 +44,14 @@ if [[ -n "$out" ]]; then
   exit 1
 fi
 
+# Do not use fmt.Errorf as it does not start a stacktrace at error site
+out="$(grep --include '*.go' -EIrn 'fmt\.Errorf?' || true)"
+if [[ -n "$out" ]]; then
+  echo >&2 "You used fmt.Errorf; use pkg/errors.Errorf instead to preserve stack traces:"
+  echo >&2 "$out"
+  exit 1
+fi
+
 # Do not initialize index.{Plugin,Platform} structs in test code.
 out="$(grep --include '*_test.go' --exclude-dir 'vendor/' -EIrn '[^]](index\.)(Plugin|Platform){' || true)"
 if [[ -n "$out" ]]; then