Lint rule: Do not override fields.

lib/src/rules/overriden_field.dart

+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+library linter.src.rules.overriden_field;
+
+import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/ast/visitor.dart';
+import 'package:analyzer/dart/element/element.dart';
+import 'package:analyzer/src/generated/resolver.dart';
+import 'package:linter/src/linter.dart';
+
+const desc = r'Do not override fields.';
+
+const details = r'''
+
+**DO** Do not override fields.
+
+**BAD:**
+```
+class Base {
+  Object field = 'lorem';
+
+  Object something = 'change';
+}
+
+class Bad1 extends Base {
+  @override
+  final field = 'ipsum'; // LINT
+}
+
+class Bad2 extends Base {
+  @override
+  Object something = 'done'; // LINT
+}
+```
+
+**GOOD:**
+```
+class Base {
+  Object field = 'lorem';
+
+  Object something = 'change';
+}
+
+class Ok extends Base {
+  Object newField; // OK
+
+  final Object newFinal = 'ignore'; // OK
+}
+```
+
+''';
+
+class OverridenField extends LintRule {
+  OverridenField()
+      : super(
+            name: 'overriden_field',
+            description: desc,
+            details: details,
+            group: Group.style);
+
+  @override
+  AstVisitor getVisitor() => new _Visitor(this);
+}
+
+class _Visitor extends SimpleAstVisitor {
+  InheritanceManager _manager;
+
+  final LintRule rule;
+  _Visitor(this.rule);
+
+  @override
+  visitCompilationUnit(CompilationUnit node) {
+    LibraryElement library = node?.element?.library;
+    _manager = library == null ? null : new InheritanceManager(library);
+  }
+
+  @override
+  visitFieldDeclaration(FieldDeclaration node) {
+    node.fields.variables.forEach((VariableDeclaration variable) {
+      ExecutableElement member = _getOverriddenMember(variable.element);
+      if (member is PropertyAccessorElement && member.isSynthetic) {
+        rule.reportLint(variable.name);
+      }
+    });
+  }
+
+  ExecutableElement _getOverriddenMember(Element member) {
+    if (member == null || _manager == null) {
+      return null;
+    }
+
+    ClassElement classElement =
+        member.getAncestor((element) => element is ClassElement);
+    if (classElement == null) {
+      return null;
+    }
+
+    return _manager.lookupInheritance(classElement, member.name);
+  }
+}