Lint rule: Do not override fields.

lib/src/rules/final_override_non_final.dart

Index: lib/src/rules/final_override_non_final.dart
diff --git a/lib/src/rules/final_override_non_final.dart b/lib/src/rules/final_override_non_final.dart
new file mode 100644
index 0000000000000000000000000000000000000000..4ad91506c7a91691297e13c0de1b3a8aadd4aa53
--- /dev/null
+++ b/lib/src/rules/final_override_non_final.dart
@@ -0,0 +1,112 @@
+// 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.final_override_non_final;

[pquitslund, 2016/04/11 16:20:32]

As per the previous comment, I think a rule name like `overridden_field` may
read slightly better.

Open to other ideas though!

[Alexei Diaz, 2016/04/11 17:30:49]

Done

+
+import 'package:linter/src/linter.dart';

[pquitslund, 2016/04/11 16:20:32]

We generally sort our members. (Alphabetically.)

In IntelliJ, that can be done using the menu Code>Sort Members in Dart File.

[Alexei Diaz, 2016/04/11 17:30:49]

I guess I overlooked it because I took for granted the dart formatter would sort
them.

+import 'package:analyzer/dart/ast/visitor.dart';
+import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/element/element.dart';
+import 'package:analyzer/src/generated/resolver.dart';
+
+const desc = r'Field overriden';

[pquitslund, 2016/04/11 16:20:32]

To stay consistent with the other lint descriptions maybe change to: 

`Do not override fields.`

[Alexei Diaz, 2016/04/11 17:30:49]

Done

+
+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 FinalOverrideNonFinal extends LintRule {
+  FinalOverrideNonFinal()
+      : super(
+            name: 'final_override_non_final',
+            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) {
+    void reportIfFinalFieldIsOverriden(VariableDeclaration variable) {
+      ExecutableElement member = _getOverriddenMember(variable.element);
+      final parentClass = member.enclosingElement as ClassElement;
+      parentClass.fields.forEach((FieldElement field) {
+        if (field.name == node.fields.variables.first.name.name &&
+            field.getter != null &&
+            field.setter != null) {
+          rule.reportLint(variable.name);
+        }
+      });
+    }
+    ;

[pquitslund, 2016/04/11 16:20:32]

Unneeded `;`?

[Alexei Diaz, 2016/04/11 17:30:50]

Done

+
+    node.fields.variables
+        .where((v) => v?.element != null && v.element.isOverride)
+        .forEach(reportIfFinalFieldIsOverriden);
+  }
+
+  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);
+  }
+}