Restore and deprecate if_invalid

Author: yevhenii-nadtochii

src/main/proto/spine/options.proto

@@ -148,7 +148,8 @@ extend google.protobuf.FieldOptions {
     //
     bool validate = 73821;
 
-    // Reserved 73822 for deleted `(if_invalid)` option.
+    // See `IfInvalidOption`.
+    IfInvalidOption if_invalid = 73822 [deprecated = true];
 
     // See `GoesOption`.
     GoesOption goes = 73823;
@@ -868,6 +869,46 @@ message PatternOption {
     }
 }
 
+// Specifies the message to show if a validated field happens to be invalid.
+//
+// It is applicable only to fields marked with `(validate)`.
+//
+message IfInvalidOption {
+
+    // Do not specify error message for `(validate)`, it is no longer used by
+    // the validation library.
+    option deprecated = true;
+
+    // The default error message.
+    option (default_message) = "The field `${parent.type}.${field.path}` of the type `${field.type}` is invalid. The field value: `${field.value}`.";
+
+    // A user-defined validation error format message.
+    //
+    // Use `error_msg` instead.
+    //
+    string msg_format = 1 [deprecated = true];
+
+    // A user-defined error message.
+    //
+    // The specified message may include the following placeholders:
+    //
+    // 1. `${field.path}` – the field path.
+    // 2. `${field.value}` - the field value.
+    // 3. `${field.type}` – the fully qualified name of the field type.
+    // 4. `${parent.type}` – the fully qualified name of the field declaring type.
+    //
+    // The placeholders will be replaced at runtime when the error is constructed.
+    //
+    // Example: Using the `(if_invalid)` option.
+    //
+    //     message Transaction {
+    //         TransactionDetails details = 1 [(validate) = true,
+    //                                         (if_invalid).error_msg = "The `${field.path}` field is invalid."];
+    //    }
+    //
+    string error_msg = 2;
+}
+
 // Specifies that another field must be present if the option's target field is present.
 //
 // Unlike the `required_field` that handles combination of required fields, this option is useful