Implement eol_at_end_of_file rule

example/all.yaml

@@ -67,6 +67,7 @@ linter:
     - empty_catches
     - empty_constructor_bodies
     - empty_statements
+    - eol_at_end_of_file
     - exhaustive_cases
     - file_names
     - flutter_style_todos

lib/src/formatter.dart

@@ -246,7 +246,10 @@ class SimpleFormatter implements ReportFormatter {
     var tableWidth = max(_summaryLength, longest + largestCountGuess);
     var pad = tableWidth - longest;
     var line = ''.padLeft(tableWidth, '-');
-    out..writeln(line)..writeln('Counts')..writeln(line);
+    out
+      ..writeln(line)
+      ..writeln('Counts')
+      ..writeln(line);
     for (var code in codes) {
       out
         ..write(code.padRight(longest))

lib/src/rules.dart

@@ -69,6 +69,7 @@ import 'rules/do_not_use_environment.dart';
 import 'rules/empty_catches.dart';
 import 'rules/empty_constructor_bodies.dart';
 import 'rules/empty_statements.dart';
+import 'rules/eol_at_end_of_file.dart';
 import 'rules/exhaustive_cases.dart';
 import 'rules/file_names.dart';
 import 'rules/flutter_style_todos.dart';
@@ -266,6 +267,7 @@ void registerLintRules({bool inTestMode = false}) {
     ..register(EmptyCatches())
     ..register(EmptyConstructorBodies())
     ..register(EmptyStatements())
+    ..register(EolAtEndOfFile())
     ..register(ExhaustiveCases())
     ..register(FileNames())
     ..register(FlutterStyleTodos())

lib/src/rules/eol_at_end_of_file.dart

@@ -0,0 +1,66 @@
+// 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:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/ast/visitor.dart';
+
+import '../analyzer.dart';
+
+const _desc = r'Put a single newline at end of file.';
+
+const _details = r'''
+
+**DO** put a single newline at the end of non-empty files.
+
+**BAD:**
+```dart
+a {
+}
+```
+
+**GOOD:**
+```dart
+b {
+}
+    <-- newline
+''';
+
+class EolAtEndOfFile extends LintRule implements NodeLintRule {
+  EolAtEndOfFile()
+      : super(
+            name: 'eol_at_end_of_file',
+            description: _desc,
+            details: _details,
+            group: Group.style);
+
+  @override
+  void registerNodeProcessors(
+      NodeLintRegistry registry, LinterContext context) {
+    var visitor = _Visitor(this, context);
+    registry.addCompilationUnit(this, visitor);
+  }
+}
+
+class _Visitor extends SimpleAstVisitor<void> {
+  final LintRule rule;
+  final LinterContext context;
+
+  _Visitor(this.rule, this.context);
+
+  @override
+  void visitCompilationUnit(CompilationUnit node) {
+    var content = context.currentUnit.content;
+    if (content.isNotEmpty &&
+        (!content.endsWithNewline || content.endsWithMultipleNewlines)) {
+      rule.reportLintForOffset(content.trimRight().length, 1);
+    }
+  }
+}
+
+extension on String {
+  bool get endsWithNewline => newline.any(endsWith);
+  static const newline = ['\n', '\r'];
+  bool get endsWithMultipleNewlines => multipleNewlines.any(endsWith);
+  static const multipleNewlines = ['\n\n', '\r\r', '\r\n\r\n'];
+}

lib/src/rules/unnecessary_getters_setters.dart

@@ -103,7 +103,9 @@ class _Visitor extends SimpleAstVisitor<void> {
         isSimpleGetter(getter) &&
         getterElement.metadata.isEmpty &&
         setterElement.metadata.isEmpty) {
-      rule..reportLint(getter.name)..reportLint(setter.name);
+      rule
+        ..reportLint(getter.name)
+        ..reportLint(setter.name);
     }
   }
 }

test/integration/eol_at_end_of_file.dart

@@ -0,0 +1,34 @@
+// 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:analyzer/src/lint/io.dart';
+import 'package:analyzer/src/lint/linter.dart';
+import 'package:linter/src/analyzer.dart';
+import 'package:linter/src/cli.dart' as cli;
+import 'package:test/test.dart';
+
+import '../mocks.dart';
+import '../test_constants.dart';
+
+void main() {
+  group('eol_at_end_of_file', () {
+    var currentOut = outSink;
+    var collectingOut = CollectingSink();
+    setUp(() => outSink = collectingOut);
+    tearDown(() {
+      collectingOut.buffer.clear();
+      outSink = currentOut;
+    });
+    test('eol at end of file', () async {
+      await cli.runLinter([
+        '$integrationTestDir/eol_at_end_of_file',
+        '--rules=eol_at_end_of_file',
+      ], LinterOptions());
+      expect(
+          collectingOut.trim(), contains('5 files analyzed, 3 issues found'));
+      expect(collectingOut.trim(),
+          contains('Put a single newline at end of file'));
+    });
+  });
+}

test_data/integration/eol_at_end_of_file/lintconfig.yaml

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

test_data/integration/eol_at_end_of_file/src/multipleComments.dart

@@ -0,0 +1,4 @@
+void multipleComments() {
+}
+// This is just a placeholder.
+// This file should be replaced with useful code.

test_data/integration/eol_at_end_of_file/src/multipleNewLines.dart

@@ -0,0 +1,3 @@
+void multipleNewlines() {
+}
+

test_data/integration/eol_at_end_of_file/src/newline.dart

@@ -0,0 +1,2 @@
+void newline() {
+}

test_data/integration/eol_at_end_of_file/src/noNewline.dart

@@ -0,0 +1,2 @@
+void noNewline() {
+}

test_data/rules/eol_at_end_of_file.dart

@@ -0,0 +1,8 @@
+// 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.
+
+// test w/ `dart test -N eol_at_end_of_file`
+
+bar() {
+} //LINT

tool/doc.dart

@@ -487,7 +487,7 @@ linter:
         .where((r) => r.maturity != Maturity.deprecated)
         .map((r) => r.name)
         .toList()
-          ..sort();
+      ..sort();
     for (var rule in sortedRules) {
       sb.write('    - $rule\n');
     }