Add type safety check for validation

urfave · Jun 27, 2023 · 51cb2ef · 51cb2ef
1 parent 6858650
commit 51cb2ef
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Showing 2 changed files with 19 additions and 2 deletions.
diff --git a/errors.go b/errors.go
@@ -199,3 +199,12 @@ func handleMultiError(multiErr MultiError) int {
 	}
 	return code
 }
+
+type typeError[T any] struct {
+	other any
+}
+
+func (te *typeError[T]) Error() string {
+	var t T
+	return fmt.Sprintf("Expected type %T got instead %T", t, te.other)
+}
diff --git a/flag_impl.go b/flag_impl.go
@@ -154,7 +154,11 @@ func (f *FlagBase[T, C, V]) Apply(set *flag.FlagSet) error {
 
 		// Validate the given default or values set from external sources as well
 		if f.Validator != nil {
-			if err := f.Validator(f.value.Get().(T)); err != nil {
+			if v, ok := f.value.Get().(T); !ok {
+				return &typeError[T]{
+					other: f.value.Get(),
+				}
+			} else if err := f.Validator(v); err != nil {
 				return err
 			}
 		}
@@ -176,7 +180,11 @@ func (f *FlagBase[T, C, V]) Apply(set *flag.FlagSet) error {
 					return err
 				}
 				if f.Validator != nil {
-					if err := f.Validator(f.value.Get().(T)); err != nil {
+					if v, ok := f.value.Get().(T); !ok {
+						return &typeError[T]{
+							other: f.value.Get(),
+						}
+					} else if err := f.Validator(v); err != nil {
 						return err
 					}
 				}