feat: add error builder property

Author: deandreamatias

example/pubspec.lock

@@ -5,10 +5,10 @@ packages:
     dependency: transitive
     description:
       name: async
-      sha256: d2872f9c19731c2e5f10444b14686eb7cc85c76274bd6c16e1816bff9a3bab63
+      sha256: "758e6d74e971c3e5aceb4110bfd6698efc7f501675bcfe0c775459a8140750eb"
       url: "https://pub.dev"
     source: hosted
-    version: "2.12.0"
+    version: "2.13.0"
   boolean_selector:
     dependency: transitive
     description:

lib/src/form_builder_field.dart

@@ -53,6 +53,7 @@ class FormBuilderField<T> extends FormField<T> {
     super.validator,
     super.restorationId,
     required super.builder,
+    super.errorBuilder,
     required this.name,
     this.valueTransformer,
     this.onChanged,

lib/src/form_builder_field_decoration.dart

@@ -19,6 +19,7 @@ class FormBuilderFieldDecoration<T> extends FormBuilderField<T> {
     super.onChanged,
     super.onReset,
     super.focusNode,
+    super.errorBuilder,
     required super.builder,
     this.decoration = const InputDecoration(),
   }) : assert(
@@ -45,15 +46,25 @@ class FormBuilderFieldDecorationState<
   F get widget => super.widget as F;
 
   /// Get the decoration with the current state
-  InputDecoration get decoration => widget.decoration.copyWith(
-    // Read only allow show error to support property skipDisabled
-    errorText:
+  InputDecoration get decoration {
+    final String? efectiveErrorText =
         widget.enabled || readOnly
             ? widget.decoration.errorText ?? errorText
-            : null,
-    enabled:
-        widget.decoration.enabled ? widget.enabled : widget.decoration.enabled,
-  );
+            : null;
+
+    return widget.decoration.copyWith(
+      // Read only allow show error to support property skipDisabled
+      errorText: widget.errorBuilder != null ? null : efectiveErrorText,
+      error:
+          widget.errorBuilder != null && efectiveErrorText != null
+              ? widget.errorBuilder!(context, efectiveErrorText)
+              : null,
+      enabled:
+          widget.decoration.enabled
+              ? widget.enabled
+              : widget.decoration.enabled,
+    );
+  }
 
   @override
   bool get hasError => super.hasError || widget.decoration.errorText != null;

pubspec.lock

@@ -5,10 +5,10 @@ packages:
     dependency: transitive
     description:
       name: async
-      sha256: d2872f9c19731c2e5f10444b14686eb7cc85c76274bd6c16e1816bff9a3bab63
+      sha256: "758e6d74e971c3e5aceb4110bfd6698efc7f501675bcfe0c775459a8140750eb"
       url: "https://pub.dev"
     source: hosted
-    version: "2.12.0"
+    version: "2.13.0"
   boolean_selector:
     dependency: transitive
     description:

test/src/form_builder_field_decoration_test.dart

@@ -43,6 +43,53 @@ void main() {
       // The field should be valid again
       expect(decorationFieldKey.currentState?.isValid, isTrue);
     });
+
+    testWidgets('when set errorBuilder then show a custom widget on error', (
+      widgetTester,
+    ) async {
+      final decorationFieldKey = GlobalKey<FormBuilderFieldDecorationState>();
+      const name = 'testField';
+      const errorTextField = 'error text field';
+      final errorTextKey = Key('errorTextKey');
+      final widget = FormBuilderFieldDecoration<String>(
+        key: decorationFieldKey,
+        name: name,
+        errorBuilder: (context, errorText) {
+          return Text(
+            errorText,
+            key: errorTextKey,
+            style: const TextStyle(color: Colors.red),
+          );
+        },
+        builder: (FormFieldState<String?> field) {
+          return InputDecorator(
+            decoration: (field as FormBuilderFieldDecorationState).decoration,
+            child: TextField(
+              onChanged: (value) {
+                field.didChange(value);
+              },
+            ),
+          );
+        },
+      );
+
+      await widgetTester.pumpWidget(buildTestableFieldWidget(widget));
+
+      // Initially, the field should be valid
+      expect(decorationFieldKey.currentState?.isValid, isTrue);
+
+      decorationFieldKey.currentState?.invalidate(errorTextField);
+
+      // The field should be invalid
+      expect(decorationFieldKey.currentState?.isValid, isFalse);
+
+      await widgetTester.pumpAndSettle();
+
+      // Check if the custom error widget is displayed
+      expect(find.text(errorTextField), findsOneWidget);
+      expect(find.byKey(errorTextKey), findsOneWidget);
+    });
+
     group('decoration enabled -', () {
       testWidgets(
         'when change the error text then the field should be invalid',