pkg/linter/lib/src/rules/unnecessary_string_interpolations.dart

// Copyright (c) 2020, 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/analysis_rule/analysis_rule.dart';
import 'package:analyzer/analysis_rule/rule_context.dart';
import 'package:analyzer/analysis_rule/rule_visitor_registry.dart';
import 'package:analyzer/dart/ast/ast.dart';
import 'package:analyzer/dart/ast/visitor.dart';
import 'package:analyzer/dart/element/nullability_suffix.dart';
import 'package:analyzer/error/error.dart';

import '../analyzer.dart';
import '../diagnostic.dart' as diag;

const _desc = r'Unnecessary string interpolation.';

class UnnecessaryStringInterpolations extends AnalysisRule {
  new()
    : super(
        name: LintNames.unnecessary_string_interpolations,
        description: _desc,
      );

  @override
  DiagnosticCode get diagnosticCode => diag.unnecessaryStringInterpolations;

  @override
  void registerNodeProcessors(
    RuleVisitorRegistry registry,
    RuleContext context,
  ) {
    var visitor = _Visitor(this);
    registry.addStringInterpolation(this, visitor);
  }
}

class _Visitor(final AnalysisRule rule) extends SimpleAstVisitor<void> {
  @override
  void visitStringInterpolation(StringInterpolation node) {
    if (node.parent is AdjacentStrings) return;
    if (node.elements.length == 3) {
      var start = node.elements.first as InterpolationString;
      var interpolation = node.elements[1] as InterpolationExpression;
      var end = node.elements[2] as InterpolationString;
      if (start.value.isEmpty && end.value.isEmpty) {
        var staticType = interpolation.expression.staticType;
        if (staticType != null &&
            staticType.isDartCoreString &&
            staticType.nullabilitySuffix != NullabilitySuffix.question) {
          rule.reportAtNode(node);
        }
      }
    }
  }
}