lib/src/rules/prefer_interpolation_to_compose_strings.dart

// Copyright (c) 2017, 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 '../analyzer.dart';
import '../util/dart_type_utilities.dart';

const _desc = r'Use interpolation to compose strings and values.';

const _details = r'''

**PREFER** using interpolation to compose strings and values.

Using interpolation when composing strings and values is usually easier to write
and read than concatenation.

**BAD:**
```
'Hello, ' + name + '! You are ' + (year - birth) + ' years old.';
```

**GOOD:**
```
'Hello, $name! You are ${year - birth} years old.';
```

''';

class PreferInterpolationToComposeStrings extends LintRule
    implements NodeLintRule {
  PreferInterpolationToComposeStrings()
      : super(
            name: 'prefer_interpolation_to_compose_strings',
            description: _desc,
            details: _details,
            group: Group.style);

  @override
  void registerNodeProcessors(
      NodeLintRegistry registry, LinterContext context) {
    final visitor = _Visitor(this);
    registry.addBinaryExpression(this, visitor);
  }
}

class _Visitor extends SimpleAstVisitor<void> {
  final LintRule rule;

  final skippedNodes = <AstNode>{};

  _Visitor(this.rule);

  @override
  void visitBinaryExpression(BinaryExpression node) {
    if (skippedNodes.contains(node)) {
      return;
    }
    if (node.operator.type == TokenType.PLUS) {
      //OK(#735): str1 + str2
      if (node.leftOperand is! StringLiteral &&
          node.rightOperand is! StringLiteral) {
        return;
      }
      //OK: 'foo' + 'bar'
      if (node.leftOperand is StringLiteral &&
          node.rightOperand is StringLiteral) {
        return;
      }
      if (DartTypeUtilities.isClass(
              node.leftOperand.staticType, 'String', 'dart.core') ||
          DartTypeUtilities.isClass(
              node.rightOperand.staticType, 'String', 'dart.core')) {
        DartTypeUtilities.traverseNodesInDFS(node).forEach(skippedNodes.add);
        rule.reportLint(node);
      }
    }
  }
}