Migrate widget field when convert Stateless-based and Stateful-based …

…to each other. (#3275)

In the official Dart `analysis_server` , when converting between
Flutter's `StatefulWidget` and `StatelessWidget`, the `widget` field
used in `StatefulWidget` is automatically added or removed.
However, this was not supported in the Assists within riverpod_lint.

In this PR, I have improved it to include the migration of that field in
the conversion.

packages/riverpod_lint/CHANGELOG.md

@@ -2,6 +2,7 @@
 
 - Fix `async_value_nullable_pattern` false positive when used with generics
   that have non-nullable type constrains.
+- Add migration widget field when convert Stateless-based and Stateful-based to each other.
 
 ## 2.3.7 - 2023-11-27
 

packages/riverpod_lint/lib/src/assists/convert_to_stateful_base_widget.dart

@@ -1,7 +1,11 @@
 import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/ast/token.dart';
+import 'package:analyzer/dart/ast/visitor.dart';
+import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/source/source_range.dart';
 // ignore: implementation_imports, somehow not exported by analyzer
 import 'package:analyzer/src/generated/source.dart' show Source;
+import 'package:analyzer_plugin/utilities/change_builder/change_builder_dart.dart';
 import 'package:collection/collection.dart';
 import 'package:custom_lint_builder/custom_lint_builder.dart';
 
@@ -83,6 +87,51 @@ class ConvertToStatefulBaseWidget extends RiverpodAssist {
       final widgetClass = node.thisOrAncestorOfType<ClassDeclaration>();
       if (widgetClass == null) return;
 
+      final nodesToMove = <ClassMember>{};
+      final elementsToMove = <Element>{};
+      final visitor = _FieldFinder();
+      for (final member in widgetClass.members) {
+        if (member is ConstructorDeclaration) {
+          member.accept(visitor);
+        }
+      }
+      final fieldsAssignedInConstructors = visitor.fieldsAssignedInConstructors;
+
+      for (final member in widgetClass.members) {
+        if (member is FieldDeclaration && !member.isStatic) {
+          for (final fieldNode in member.fields.variables) {
+            final fieldElement = fieldNode.declaredElement as FieldElement?;
+            if (fieldElement == null) continue;
+            if (!fieldsAssignedInConstructors.contains(fieldElement)) {
+              nodesToMove.add(member);
+              elementsToMove.add(fieldElement);
+
+              final getter = fieldElement.getter;
+              if (getter != null) {
+                elementsToMove.add(getter);
+              }
+
+              final setter = fieldElement.setter;
+              if (setter != null) {
+                elementsToMove.add(setter);
+              }
+            }
+          }
+        } else if (member is MethodDeclaration && !member.isStatic) {
+          nodesToMove.add(member);
+          elementsToMove.add(member.declaredElement!);
+        }
+      }
+
+      for (final node in nodesToMove) {
+        final visitor = _ReplacementEditBuilder(
+          widgetClass.declaredElement!,
+          elementsToMove,
+          builder,
+        );
+        node.accept(visitor);
+      }
+
       final buildMethod = node
           .thisOrAncestorOfType<ClassDeclaration>()
           ?.members
@@ -186,3 +235,78 @@ class $createdStateClassName extends $baseStateName<${widgetClass.name}> {
     });
   }
 }
+
+// Original implemenation in
+// package:analysis_server/lib/src/services/correction/dart/flutter_convert_to_stateful_widget.dart
+class _FieldFinder extends RecursiveAstVisitor<void> {
+  Set<FieldElement> fieldsAssignedInConstructors = {};
+
+  @override
+  void visitFieldFormalParameter(FieldFormalParameter node) {
+    final element = node.declaredElement;
+    if (element is FieldFormalParameterElement) {
+      final field = element.field;
+      if (field != null) {
+        fieldsAssignedInConstructors.add(field);
+      }
+    }
+
+    super.visitFieldFormalParameter(node);
+  }
+
+  @override
+  void visitSimpleIdentifier(SimpleIdentifier node) {
+    if (node.parent is ConstructorFieldInitializer) {
+      final element = node.staticElement;
+      if (element is FieldElement) {
+        fieldsAssignedInConstructors.add(element);
+      }
+    }
+    if (node.inSetterContext()) {
+      final element = node.writeOrReadElement;
+      if (element is PropertyAccessorElement) {
+        final field = element.variable;
+        if (field is FieldElement) {
+          fieldsAssignedInConstructors.add(field);
+        }
+      }
+    }
+  }
+}
+
+class _ReplacementEditBuilder extends RecursiveAstVisitor<void> {
+  _ReplacementEditBuilder(
+    this.widgetClassElement,
+    this.elementsToMove,
+    this.builder,
+  );
+
+  final ClassElement widgetClassElement;
+  final Set<Element> elementsToMove;
+  final DartFileEditBuilder builder;
+
+  @override
+  void visitSimpleIdentifier(SimpleIdentifier node) {
+    if (node.inDeclarationContext()) {
+      return;
+    }
+    final element = node.staticElement;
+    if (element is ExecutableElement &&
+        element.enclosingElement == widgetClassElement &&
+        !elementsToMove.contains(element)) {
+      final offset = node.offset;
+      final qualifier =
+          element.isStatic ? widgetClassElement.displayName : 'widget';
+
+      final parent = node.parent;
+      if (parent is InterpolationExpression &&
+          parent.leftBracket.type ==
+              TokenType.STRING_INTERPOLATION_IDENTIFIER) {
+        builder.addSimpleInsertion(offset, '{$qualifier.');
+        builder.addSimpleInsertion(offset + node.length, '}');
+      } else {
+        builder.addSimpleInsertion(offset, '$qualifier.');
+      }
+    }
+  }
+}