Return a typed error for config validation, and make errors simple

Will allow clients to determine when the configuration is bad.

pkg/client/clientcmd/validation.go

@@ -43,10 +43,47 @@ func IsContextNotFound(err error) bool {
 	if err == nil {
 		return false
 	}
-
+	if _, ok := err.(*errContextNotFound); ok || err == ErrNoContext {
+		return true
+	}
 	return strings.Contains(err.Error(), "context was not found for specified context")
 }
 
+// errConfigurationInvalid is a set of errors indicating the configuration is invalid.
+type errConfigurationInvalid []error
+
+// errConfigurationInvalid implements error and Aggregate
+var _ error = errConfigurationInvalid{}
+var _ utilerrors.Aggregate = errConfigurationInvalid{}
+
+func newErrConfigurationInvalid(errs []error) error {
+	switch len(errs) {
+	case 0:
+		return nil
+	default:
+		return errConfigurationInvalid(errs)
+	}
+}
+
+// Error implements the error interface
+func (e errConfigurationInvalid) Error() string {
+	return fmt.Sprintf("invalid configuration: %v", utilerrors.NewAggregate(e).Error())
+}
+
+// Errors implements the AggregateError interface
+func (e errConfigurationInvalid) Errors() []error {
+	return e
+}
+
+// IsConfigurationInvalid returns true if the provided error indicates the configuration is invalid.
+func IsConfigurationInvalid(err error) bool {
+	switch err.(type) {
+	case *errContextNotFound, errConfigurationInvalid:
+		return true
+	}
+	return IsContextNotFound(err)
+}
+
 // Validate checks for errors in the Config.  It does not return early so that it can find as many errors as possible.
 func Validate(config clientcmdapi.Config) error {
 	validationErrors := make([]error, 0)
@@ -69,7 +106,7 @@ func Validate(config clientcmdapi.Config) error {
 		validationErrors = append(validationErrors, validateClusterInfo(clusterName, clusterInfo)...)
 	}
 
-	return utilerrors.NewAggregate(validationErrors)
+	return newErrConfigurationInvalid(validationErrors)
 }
 
 // ConfirmUsable looks a particular context and determines if that particular part of the config is useable.  There might still be errors in the config,
@@ -99,7 +136,7 @@ func ConfirmUsable(config clientcmdapi.Config, passedContextName string) error {
 		validationErrors = append(validationErrors, validateClusterInfo(context.Cluster, config.Clusters[context.Cluster])...)
 	}
 
-	return utilerrors.NewAggregate(validationErrors)
+	return newErrConfigurationInvalid(validationErrors)
 }
 
 // validateClusterInfo looks for conflicts and errors in the cluster info
@@ -107,7 +144,11 @@ func validateClusterInfo(clusterName string, clusterInfo clientcmdapi.Cluster) [
 	validationErrors := make([]error, 0)
 
 	if len(clusterInfo.Server) == 0 {
-		validationErrors = append(validationErrors, fmt.Errorf("no server found for %v", clusterName))
+		if len(clusterName) == 0 {
+			validationErrors = append(validationErrors, fmt.Errorf("default cluster has no server defined"))
+		} else {
+			validationErrors = append(validationErrors, fmt.Errorf("no server found for cluster %q", clusterName))
+		}
 	}
 	// Make sure CA data and CA file aren't both specified
 	if len(clusterInfo.CertificateAuthority) != 0 && len(clusterInfo.CertificateAuthorityData) != 0 {
@@ -155,7 +196,7 @@ func validateAuthInfo(authInfoName string, authInfo clientcmdapi.AuthInfo) []err
 		}
 		// Make sure key data and file aren't both specified
 		if len(authInfo.ClientKey) != 0 && len(authInfo.ClientKeyData) != 0 {
-			validationErrors = append(validationErrors, fmt.Errorf("client-key-data and client-key are both specified for %v. client-key-data will override.", authInfoName))
+			validationErrors = append(validationErrors, fmt.Errorf("client-key-data and client-key are both specified for %v; client-key-data will override", authInfoName))
 		}
 		// Make sure a key is specified
 		if len(authInfo.ClientKey) == 0 && len(authInfo.ClientKeyData) == 0 {
@@ -180,7 +221,7 @@ func validateAuthInfo(authInfoName string, authInfo clientcmdapi.AuthInfo) []err
 
 	// authPath also provides information for the client to identify the server, so allow multiple auth methods in that case
 	if (len(methods) > 1) && (!usingAuthPath) {
-		validationErrors = append(validationErrors, fmt.Errorf("more than one authentication method found for  %v.  Found %v, only one is allowed", authInfoName, methods))
+		validationErrors = append(validationErrors, fmt.Errorf("more than one authentication method found for %v; found %v, only one is allowed", authInfoName, methods))
 	}
 
 	return validationErrors
@@ -191,19 +232,19 @@ func validateContext(contextName string, context clientcmdapi.Context, config cl
 	validationErrors := make([]error, 0)
 
 	if len(context.AuthInfo) == 0 {
-		validationErrors = append(validationErrors, fmt.Errorf("user was not specified for Context %v", contextName))
+		validationErrors = append(validationErrors, fmt.Errorf("user was not specified for context %q", contextName))
 	} else if _, exists := config.AuthInfos[context.AuthInfo]; !exists {
-		validationErrors = append(validationErrors, fmt.Errorf("user, %v, was not found for Context %v", context.AuthInfo, contextName))
+		validationErrors = append(validationErrors, fmt.Errorf("user %q was not found for context %q", context.AuthInfo, contextName))
 	}
 
 	if len(context.Cluster) == 0 {
-		validationErrors = append(validationErrors, fmt.Errorf("cluster was not specified for Context %v", contextName))
+		validationErrors = append(validationErrors, fmt.Errorf("cluster was not specified for context %q", contextName))
 	} else if _, exists := config.Clusters[context.Cluster]; !exists {
-		validationErrors = append(validationErrors, fmt.Errorf("cluster, %v, was not found for Context %v", context.Cluster, contextName))
+		validationErrors = append(validationErrors, fmt.Errorf("cluster %q was not found for context %q", context.Cluster, contextName))
 	}
 
 	if (len(context.Namespace) != 0) && !util.IsDNS952Label(context.Namespace) {
-		validationErrors = append(validationErrors, fmt.Errorf("namespace, %v, for context %v, does not conform to the kubernetes DNS952 rules", context.Namespace, contextName))
+		validationErrors = append(validationErrors, fmt.Errorf("namespace %q for context %q does not conform to the kubernetes DNS952 rules", context.Namespace, contextName))
 	}
 
 	return validationErrors