+ unnecessary_breaks (dart-archive/linter#3981)

* + unnecessary_breaks

* ++

* --

* feedback

* typo

* + pattern feature checking

Author: pq

example/all.yaml

@@ -167,6 +167,7 @@ linter:
     - unawaited_futures
     - unnecessary_await_in_return
     - unnecessary_brace_in_string_interps
+    - unnecessary_breaks
     - unnecessary_const
     - unnecessary_constructor_name
     - unnecessary_final

lib/src/rules.dart

@@ -176,6 +176,7 @@ import 'rules/type_init_formals.dart';
 import 'rules/unawaited_futures.dart';
 import 'rules/unnecessary_await_in_return.dart';
 import 'rules/unnecessary_brace_in_string_interps.dart';
+import 'rules/unnecessary_breaks.dart';
 import 'rules/unnecessary_const.dart';
 import 'rules/unnecessary_constructor_name.dart';
 import 'rules/unnecessary_final.dart';
@@ -399,6 +400,7 @@ void registerLintRules({bool inTestMode = false}) {
     ..register(UnawaitedFutures())
     ..register(UnnecessaryAwaitInReturn())
     ..register(UnnecessaryBraceInStringInterps())
+    ..register(UnnecessaryBreaks())
     ..register(UnnecessaryConst())
     ..register(UnnecessaryConstructorName())
     ..register(UnnecessaryFinal())

lib/src/rules/unnecessary_breaks.dart

@@ -0,0 +1,100 @@
+// Copyright (c) 2023, 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/analysis/features.dart';
+import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/ast/visitor.dart';
+
+import '../analyzer.dart';
+
+const _desc = r"Don't use explicit `break`s when a break is implied.";
+
+const _details = r'''
+Only use a `break` in a non-empty switch case statement if you need to break
+before the end of the case body.  Dart does not support fallthrough execution
+for non-empty cases, so `break`s at the end of non-empty switch case statements
+are unnecessary.
+
+**BAD:**
+```dart
+switch (1) {
+  case 1:
+    print("one");
+    break;
+  case 2:
+    print("two");
+    break;
+}
+```
+
+**GOOD:**
+```dart
+switch (1) {
+  case 1:
+    print("one");
+  case 2:
+    print("two");
+}
+```
+
+```dart
+switch (1) {
+  case 1:
+  case 2:
+    print("one or two");
+}
+```
+
+```dart
+switch (1) {
+  case 1:
+    break;
+  case 2:
+    print("just two");
+}
+```
+''';
+
+class UnnecessaryBreaks extends LintRule {
+  static const LintCode code = LintCode(
+      'unnecessary_breaks', "Unnecessary 'break' statement.",
+      correctionMessage: "Try removing the 'break'.");
+
+  UnnecessaryBreaks()
+      : super(
+            name: 'unnecessary_breaks',
+            description: _desc,
+            details: _details,
+            group: Group.style);
+
+  @override
+  LintCode get lintCode => code;
+
+  @override
+  void registerNodeProcessors(
+      NodeLintRegistry registry, LinterContext context) {
+    if (!context.isEnabled(Feature.patterns)) return;
+    var visitor = _Visitor(this);
+    registry.addBreakStatement(this, visitor);
+  }
+}
+
+class _Visitor extends SimpleAstVisitor {
+  final LintRule rule;
+
+  _Visitor(this.rule);
+
+  @override
+  visitBreakStatement(BreakStatement node) {
+    if (node.label != null) return;
+    var parent = node.parent;
+    if (parent is SwitchPatternCase) {
+      var statements = parent.statements;
+      if (statements.length == 1) return;
+      if (node == statements.last) {
+        rule.reportLint(node);
+      }
+    }
+  }
+}

test/rules/all.dart

@@ -84,6 +84,7 @@ import 'type_init_formals_test.dart' as type_init_formals;
 import 'unawaited_futures_test.dart' as unawaited_futures;
 import 'unnecessary_brace_in_string_interps_test.dart'
     as unnecessary_brace_in_string_interps;
+import 'unnecessary_breaks_test.dart' as unnecessary_breaks;
 import 'unnecessary_const_test.dart' as unnecessary_const;
 import 'unnecessary_null_checks_test.dart' as unnecessary_null_checks;
 import 'unnecessary_overrides_test.dart' as unnecessary_overrides;
@@ -155,6 +156,7 @@ void main() {
   type_init_formals.main();
   unawaited_futures.main();
   unnecessary_brace_in_string_interps.main();
+  unnecessary_breaks.main();
   unnecessary_const.main();
   unnecessary_null_checks.main();
   unnecessary_overrides.main();

test/rules/unnecessary_breaks_test.dart

@@ -0,0 +1,111 @@
+// Copyright (c) 2023, 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(UnnecessaryBreaksTest);
+  });
+}
+
+@reflectiveTest
+class UnnecessaryBreaksTest extends LintRuleTest {
+  @override
+  List<String> get experiments => ['patterns', 'records'];
+
+  @override
+  String get lintRule => 'unnecessary_breaks';
+
+  test_switch_pre30_ok() async {
+    await assertNoDiagnostics(r'''
+// @dart=2.19    
+f() {
+  switch (1) {
+    case 1:
+      f();
+      break;
+  }
+}
+''');
+  }
+
+  test_switchPatternCase() async {
+    await assertDiagnostics(r'''
+f() {
+  switch (1) {
+    case 1:
+      f();
+      break;
+    case 2:
+      f();
+  }
+}
+''', [
+      lint(50, 6),
+    ]);
+  }
+
+  test_switchPatternCase_empty_ok() async {
+    await assertNoDiagnostics(r'''
+f() {
+  switch (1) {
+    case 1:
+      break;
+    case 2:
+      f();
+  }
+}
+''');
+  }
+
+  test_switchPatternCase_labeled_ok() async {
+    await assertNoDiagnostics(
+      r'''
+f() {
+  l:
+  switch (1) {
+    case 1:
+      break l;
+    case 2:
+      f();
+  }
+}
+''',
+    );
+  }
+
+  test_switchPatternCase_notDirectChild_ok() async {
+    await assertNoDiagnostics(r'''
+f(bool c) {
+  switch (1) {
+    case 1:
+      if (c) break;
+      f(true);
+    case 2:
+      f(true);
+  }
+}
+''');
+  }
+
+  test_switchPatternCase_notLast_ok() async {
+    await assertDiagnostics(r'''
+f(bool c) {
+  switch (1) {
+    case 1:
+      break;
+      f(true);
+    case 2:
+      f(true);
+  }
+}
+''', [
+      // No lint.
+      error(HintCode.DEAD_CODE, 58, 8),
+    ]);
+  }
+}