spread_collections experiment

lib/src/rules/experiments/spread_collections.dart

@@ -0,0 +1,109 @@
+// Copyright (c) 2019, 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/token.dart';
+import 'package:analyzer/dart/ast/visitor.dart';
+import 'package:linter/src/analyzer.dart';
+
+const _desc = r'Use spread collections when possible.';
+
+const _details = r'''
+
+Use spread collections when possible.
+
+Collection literals are excellent when you want to create a new collection out 
+of individual items. But, when existing items are already stored in another 
+collection, spread collection syntax leads to simpler code.
+
+**BAD:**
+
+```
+Widget build(BuildContext context) {
+  return CupertinoPageScaffold(
+    child: ListView(
+      children: [
+        Tab2Header(),
+      ]..addAll(buildTab2Conversation()),
+    ),
+  );
+}
+```
+
+```
+var ints = [1, 2, 3];
+print(['a']..addAll(ints.map((i) => i.toString()))..addAll(['c']));
+```
+
+```
+var things;
+var l = ['a']..addAll(things ?? const []);
+```
+
+
+**GOOD:**
+
+```
+Widget build(BuildContext context) {
+  return CupertinoPageScaffold(
+    child: ListView(
+      children: [
+        Tab2Header(),
+        ...buildTab2Conversation(),
+      ],
+    ),
+  );
+}
+```
+
+```
+var ints = [1, 2, 3];
+print(['a', ...ints.map((i) => i.toString()), 'c');
+```
+
+```
+var things;
+var l = ['a', ...?things];
+```
+''';
+
+class SpreadCollections extends LintRule implements NodeLintRule {
+  SpreadCollections()
+      : super(
+            name: 'spread_collections',
+            description: _desc,
+            details: _details,
+            group: Group.style);
+
+  @override
+  void registerNodeProcessors(NodeLintRegistry registry,
+      [LinterContext context]) {
+    final visitor = new _Visitor(this);
+    registry.addMethodInvocation(this, visitor);
+  }
+}
+
+class _Visitor extends SimpleAstVisitor<void> {
+  final LintRule rule;
+
+  _Visitor(this.rule);
+
+  @override
+  void visitMethodInvocation(MethodInvocation invocation) {
+    if (invocation.methodName.name != 'addAll' ||
+        !invocation.isCascaded ||
+        invocation.argumentList.arguments.length != 1) {
+      return;
+    }
+
+    CascadeExpression cascade = invocation.thisOrAncestorOfType();
+    NodeList<Expression> sections = cascade.cascadeSections;
+    Expression target = cascade.target;
+    if (target is! ListLiteral || sections[0] != invocation) {
+      return;
+    }
+
+    rule.reportLint(invocation.methodName);
+  }
+}

test/integration_test.dart

@@ -13,6 +13,7 @@ import 'package:test/test.dart';
 import 'package:yaml/yaml.dart';
 
 import 'mocks.dart';
+import 'rules/experiments/experiments.dart';
 
 main() {
   defineTests();
@@ -820,7 +821,9 @@ defineTests() {
         expect(
             configuredLints,
             unorderedEquals(Analyzer.facade.registeredRules
-                .where((r) => r.maturity != Maturity.deprecated)
+                .where((r) =>
+                    r.maturity != Maturity.deprecated &&
+                    !experiments.contains(r))
                 .map((r) => r.name)));
       });
     });

test/rule_test.dart

@@ -25,6 +25,7 @@ import 'package:path/path.dart' as p;
 import 'package:test/test.dart';
 
 import 'mock_sdk.dart';
+import 'rules/experiments/experiments.dart';
 
 main() {
   defineSanityTests();
@@ -56,6 +57,22 @@ defineRuleTests() {
 //        });
 //      }
     });
+    group('experiments', () {
+      registerLintRuleExperiments();
+
+      for (var entry
+          in new Directory(p.join(ruleDir, 'experiments')).listSync()) {
+        if (entry is! Directory) continue;
+        var analysisOptionsFile =
+            new File(p.join(entry.path, 'analysis_options.yaml'));
+        var analysisOptions = analysisOptionsFile.readAsStringSync();
+        var ruleName = p.basename(entry.path);
+        var testFile = new File(p.join(entry.path, '$ruleName.dart'));
+        testRule(p.basename(ruleName), testFile,
+            analysisOptions: analysisOptions);
+      }
+    });
+
     group('pub', () {
       for (var entry in new Directory(p.join(ruleDir, 'pub')).listSync()) {
         if (entry is! Directory) continue;

test/rules/experiments/experiments.dart

@@ -0,0 +1,16 @@
+// Copyright (c) 2019, 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:linter/src/analyzer.dart';
+import 'package:linter/src/rules/experiments/spread_collections.dart';
+
+
+final experiments = [
+  new SpreadCollections(),
+];
+
+void registerLintRuleExperiments() {
+  experiments.forEach(Analyzer.facade.register);
+}
+

test/rules/experiments/spread_collections/analysis_options.yaml

@@ -0,0 +1,3 @@
+analyzer:
+  enable-experiment:
+    - control-flow-collections

test/rules/experiments/spread_collections/spread_collections.dart

@@ -0,0 +1,33 @@
+// Copyright (c) 2019, 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.
+
+
+f() {
+  var ints = [1, 2, 3];
+  print(['a']..addAll(ints.map((i) => i.toString()))..addAll(['c'])); // LINT
+}
+
+var l = ['a']..addAll(['b']); // LINT
+
+var l1 = [];
+var l2 = l1..addAll(['b']); //OK
+
+var things;
+var l3 = ['a']..addAll(things ?? const []); // LINT
+var l4 = ['a']..addAll(things ?? []); //LINT
+
+// Control flow.
+
+bool condition;
+var l5 = ['a']..addAll(condition ? things : const []); // LINT
+var l6 = ['a']..addAll(condition ? things : []); // LINT
+
+class A {
+ void addAll(Iterable iterable) { }
+}
+
+g() {
+  new A()..addAll(['a']); // OK
+}
+