Fix overriden_field false positive (#246).

Fixes: https://github.com/dart-lang/linter/issues/246

Net-net: we need to ensure that the overridden field is in the same library as the overrider.

BUG=
[email protected]

Review URL: https://codereview.chromium.org//1991283003 .

Author: pq

lib/src/rules/overriden_field.dart

@@ -113,8 +113,9 @@ class _Visitor extends SimpleAstVisitor {
 
   PropertyAccessorElement _getOverriddenMember(Element member) {
     String memberName = member.name;
+    LibraryElement library = member.library;
     bool isOverriddenMember(PropertyAccessorElement a) =>
-        a.isSynthetic && a.name == memberName;
+        a.library == library && a.isSynthetic && a.name == memberName;
     bool containsOverridenMember(InterfaceType i) =>
         i.accessors.any(isOverriddenMember);
     ClassElement classElement = member.enclosingElement;

test/_data/overridden_field/lintconfig.yaml

@@ -0,0 +1,2 @@
+rules:
+  - overridden_field

test/_data/overridden_field/src/a.dart

@@ -0,0 +1,4 @@
+/// A.
+class A {
+  int _hidden;
+}

test/_data/overridden_field/src/b.dart

@@ -0,0 +1,6 @@
+import 'a.dart';
+
+/// B.
+class B extends A {
+  int _hidden;
+}

test/integration_test.dart

@@ -150,6 +150,32 @@ defineTests() {
       });
     });
 
+    group('overridden_field', () {
+      IOSink currentOut = outSink;
+      CollectingSink collectingOut = new CollectingSink();
+      setUp(() {
+        exitCode = 0;
+        outSink = collectingOut;
+      });
+      tearDown(() {
+        collectingOut.buffer.clear();
+        outSink = currentOut;
+        exitCode = 0;
+      });
+
+      // https://github.com/dart-lang/linter/issues/246
+      test('overrides across libraries', () {
+        dartlint.main([
+          'test/_data/overridden_field',
+          '-c',
+          'test/_data/overridden_field/lintconfig.yaml'
+        ]);
+        expect(exitCode, 0);
+        expect(collectingOut.trim(),
+            stringContainsInOrder(['2 files analyzed, 0 issues found, in']));
+      });
+    });
+
     group('examples', () {
       test('lintconfig.yaml', () {
         var src = readFile('example/lintconfig.yaml');