Issues #92, #148: refactor to use common code between two rules (#221)

* Issues #92, #148: refactor to use common code between two rules

* Issues #92, #148: fixed code formatting

* Issues #92, #148: simplified to use expr.accept(visitor)

* Issues #92, #148: removed unnecessary super call

Author: tozpeak

lib/src/common/visitors/select_expression_identifiers_visitor.dart

@@ -0,0 +1,15 @@
+import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/ast/visitor.dart';
+
+/// This visitor is used to select all SimpleIdentifiers from Expression
+class SelectExpressionIdentifiersVisitor extends RecursiveAstVisitor<void> {
+  final _identifiers = <SimpleIdentifier>{};
+
+  /// List of SimpleIdentifiers mentioned in expression
+  Set<SimpleIdentifier> get identifiers => _identifiers;
+
+  @override
+  void visitSimpleIdentifier(SimpleIdentifier node) {
+    _identifiers.add(node);
+  }
+}

lib/src/lints/avoid_unnecessary_return_variable/avoid_unnecessary_return_variable_rule.dart

@@ -2,6 +2,7 @@ import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element2.dart';
 import 'package:analyzer/error/listener.dart';
 import 'package:custom_lint_builder/custom_lint_builder.dart';
+import 'package:solid_lints/src/common/visitors/select_expression_identifiers_visitor.dart';
 import 'package:solid_lints/src/lints/avoid_unnecessary_return_variable/visitors/avoid_unnecessary_return_variable_visitor.dart';
 import 'package:solid_lints/src/models/rule_config.dart';
 import 'package:solid_lints/src/models/solid_lint_rule.dart';
@@ -116,23 +117,10 @@ Rewrite the variable evaluation into return statement instead.""",
   }
 
   bool _isExpressionImmutable(Expression expr) {
-    switch (expr) {
-      case Literal _:
-        return true;
-
-      case final PrefixedIdentifier prefixed:
-        return _isExpressionImmutable(prefixed.prefix) &&
-            _isExpressionImmutable(prefixed.identifier);
-
-      case final BinaryExpression binExpr:
-        return _isExpressionImmutable(binExpr.leftOperand) &&
-            _isExpressionImmutable(binExpr.rightOperand);
+    final visitor = SelectExpressionIdentifiersVisitor();
+    expr.accept(visitor);
 
-      case final SimpleIdentifier identifier:
-        return _isSimpleIdentifierImmutable(identifier);
-    }
-
-    return false;
+    return visitor.identifiers.every(_isSimpleIdentifierImmutable);
   }
 
   bool _isSimpleIdentifierImmutable(SimpleIdentifier identifier) {