wip: add provider generator.

app/lib/builder/provider_annotation.dart

@@ -0,0 +1,9 @@
+class ProviderModel {
+  const ProviderModel();
+}
+
+class ProviderModelProp {
+  const ProviderModelProp({this.nullable = true});
+
+  final bool nullable;
+}

app/lib/builder/provider_builder.dart

@@ -0,0 +1,6 @@
+import 'package:dde_gesture_manager/builder/provider_generator.dart';
+import 'package:source_gen/source_gen.dart';
+import 'package:build/build.dart';
+
+Builder providerBuilder(BuilderOptions options) =>
+    LibraryBuilder(ProviderGenerator(), generatedExtension: '.provider.dart');

app/lib/builder/provider_generator.dart

@@ -0,0 +1,48 @@
+import 'package:analyzer/dart/element/element.dart';
+import 'package:build/src/builder/build_step.dart';
+import 'package:dde_gesture_manager/builder/provider_annotation.dart';
+import 'package:source_gen/source_gen.dart';
+import 'package:collection/collection.dart';
+
+class AnnotationField {
+  String name;
+  String type;
+
+  AnnotationField(this.name, this.type);
+}
+
+class ProviderGenerator extends GeneratorForAnnotation<ProviderModel> {
+  @override
+  generateForAnnotatedElement(Element element, ConstantReader annotation, BuildStep buildStep) {
+    var className = (element as ClassElement).source.shortName;
+    List<AnnotationField> fields = [];
+    element.fields.forEach((field) {
+      var annotation = field.metadata.firstWhereOrNull(
+          (m) => m.computeConstantValue()?.type?.getDisplayString(withNullability: true) == 'ProviderModelProp');
+      if (annotation != null)
+        fields.add(
+          AnnotationField(
+            field.displayName,
+            field.type.getDisplayString(
+              withNullability: annotation.computeConstantValue()?.getField('nullable')?.toBoolValue() ?? true,
+            ),
+          ),
+        );
+    });
+    return '''
+import 'package:flutter/foundation.dart';
+import 'package:dde_gesture_manager/extensions/compare_extension.dart';
+import '$className';
+
+class ${element.displayName}Provider extends ${element.displayName} with ChangeNotifier {
+  void setProps({
+    ${fields.map((f) => '${f.type.endsWith('?') ? '' : 'required '}${f.type} ${f.name},').join('\n')}
+  }) {
+    bool changed = false;    
+    ${fields.map((f) => 'if (${f.name}.diff(this.${f.name})) {this.${f.name} = ${f.name}; changed = true; }').join('\n')}
+    if (changed) notifyListeners();
+  }
+}
+    ''';
+  }
+}