fix file_names diagnostic offset (dart-lang/linter#3020)

* fix file_names diagnostic offset

* test fix

lib/src/rules/file_names.dart

@@ -70,7 +70,7 @@ class _Visitor extends SimpleAstVisitor<void> {
     if (declaredElement != null) {
       var fileName = declaredElement.source.shortName;
       if (!isValidDartFileName(fileName)) {
-        rule.reportLint(node);
+        rule.reportLintForOffset(0, 0);
       }
     }
   }

test/integration_test.dart

@@ -28,7 +28,6 @@ import 'integration/depend_on_referenced_packages.dart'
     as depend_on_referenced_packages;
 import 'integration/directives_ordering.dart' as directives_ordering;
 import 'integration/exhaustive_cases.dart' as exhaustive_cases;
-import 'integration/file_names.dart' as file_names;
 import 'integration/flutter_style_todos.dart' as flutter_style_todos;
 import 'integration/lines_longer_than_80_chars.dart'
     as lines_longer_than_80_chars;
@@ -190,7 +189,6 @@ void ruleTests() {
     cancel_subscriptions.main();
     depend_on_referenced_packages.main();
     directives_ordering.main();
-    file_names.main();
     flutter_style_todos.main();
     lines_longer_than_80_chars.main();
     only_throw_errors.main();

test/rules/all.dart

@@ -7,6 +7,7 @@ import 'avoid_function_literals_in_foreach_calls.dart'
 import 'avoid_init_to_null.dart' as avoid_init_to_null;
 import 'avoid_shadowing_type_parameters.dart'
     as avoid_shadowing_type_parameters;
+import 'file_names.dart' as file_names;
 import 'missing_whitespace_between_adjacent_strings.dart'
     as missing_whitespace_between_adjacent_strings;
 import 'non_constant_identifier_names.dart' as non_constant_identifier_names;
@@ -35,6 +36,7 @@ void main() {
   avoid_function_literals_in_foreach_calls.main();
   avoid_init_to_null.main();
   avoid_shadowing_type_parameters.main();
+  file_names.main();
   missing_whitespace_between_adjacent_strings.main();
   non_constant_identifier_names.main();
   null_closures.main();

test/rules/file_names.dart

@@ -0,0 +1,46 @@
+// Copyright (c) 2021, 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.
+
+import 'package:test_reflective_loader/test_reflective_loader.dart';
+
+import '../rule_test_support.dart';
+
+main() {
+  defineReflectiveSuite(() {
+    defineReflectiveTests(FileNamesInvalidTest);
+    defineReflectiveTests(FileNamesNonStrictTest);
+  });
+}
+
+@reflectiveTest
+class FileNamesInvalidTest extends LintRuleTest {
+  @override
+  String get lintRule => 'file_names';
+
+  @override
+  String get testFilePath => '$testPackageLibPath/a-test.dart';
+
+  test_invalidName() async {
+    await assertDiagnostics(r'''
+class A { }
+''', [
+      lint('file_names', 0, 0),
+    ]);
+  }
+}
+
+@reflectiveTest
+class FileNamesNonStrictTest extends LintRuleTest {
+  @override
+  String get lintRule => 'file_names';
+
+  @override
+  String get testFilePath => '$testPackageLibPath/non-strict.css.dart';
+
+  test_validName() async {
+    await assertNoDiagnostics(r'''
+class A { }
+''');
+  }
+}