Issue 22188. Verify that none or all execution flows return.

pkg/analysis_server/lib/src/services/refactoring/extract_method.dart

 // Copyright (c) 2014, 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.
 
 library services.src.refactoring.extract_method;
 
 import 'dart:async';
 
 import 'package:analysis_server/src/protocol_server.dart' hide Element;
 import 'package:analysis_server/src/services/correction/name_suggestion.dart';
 import 'package:analysis_server/src/services/correction/selection_analyzer.dart';
 import 'package:analysis_server/src/services/correction/source_range.dart';
 import 'package:analysis_server/src/services/correction/statement_analyzer.dart';
 import 'package:analysis_server/src/services/correction/status.dart';
 import 'package:analysis_server/src/services/correction/util.dart';
 import 'package:analysis_server/src/services/refactoring/naming_conventions.dart';
 import 'package:analysis_server/src/services/refactoring/refactoring.dart';
 import 'package:analysis_server/src/services/refactoring/refactoring_internal.dart';
 import 'package:analysis_server/src/services/refactoring/rename_class_member.dart';
 import 'package:analysis_server/src/services/refactoring/rename_unit_member.dart';
 import 'package:analysis_server/src/services/search/element_visitors.dart';
 import 'package:analysis_server/src/services/search/search_engine.dart';
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/java_core.dart';
 import 'package:analyzer/src/generated/scanner.dart';
 import 'package:analyzer/src/generated/source.dart';
+import 'package:analyzer/src/generated/resolver.dart' show ExitDetector;
 
 
 const String _TOKEN_SEPARATOR = '\uFFFF';
 
 
 /**
  * Returns the "normalized" version of the given source, which is reconstructed
  * from tokens, so ignores all the comments and spaces.
  */
 String _getNormalizedSource(String src) {
@@ skipping 12 matching lines @@
   });
   return result;
 }
 
 
 /**
  * [ExtractMethodRefactoring] implementation.
  */
 class ExtractMethodRefactoringImpl extends RefactoringImpl implements
     ExtractMethodRefactoring {
+  static const ERROR_EXITS =
+      'Selected statements contain a return statement, but not all possible '
+          'execuion flows exit. Semantics may not be preserved.';
+
   final SearchEngine searchEngine;
   final CompilationUnit unit;
   final int selectionOffset;
   final int selectionLength;
   CompilationUnitElement unitElement;
   SourceRange selectionRange;
   CorrectionUtils utils;
 
   String returnType;
   String name;
@@ skipping 495 matching lines @@
     _parameters.clear();
     _parametersMap.clear();
     _parameterReferencesMap.clear();
     RefactoringStatus result = new RefactoringStatus();
     List<VariableElement> assignedUsedVariables = [];
     unit.accept(new _InitializeParametersVisitor(this, assignedUsedVariables));
     // single expression
     if (_selectionExpression != null) {
       _returnType = _selectionExpression.bestType;
     }
-    // may be ends with "return" statement
+    // verify that none or all execution flows end with a "return"
+    if (_selectionStatements != null) {
+      bool hasReturn = _selectionStatements.any(_mayEndWithReturnStatement);
+      if (hasReturn && !ExitDetector.exits(_selectionStatements.last)) {
+        result.addError(ERROR_EXITS);
+      }
+    }
+    // maybe ends with "return" statement
     if (_selectionStatements != null) {
       _ReturnTypeComputer returnTypeComputer = new _ReturnTypeComputer();
       _selectionStatements.forEach((statement) {
         statement.accept(returnTypeComputer);
       });
       _returnType = returnTypeComputer.returnType;
     }
-    // may be single variable to return
+    // maybe single variable to return
     if (assignedUsedVariables.length == 1) {
       // we cannot both return variable and have explicit return statement
       if (_returnType != null) {
         result.addFatalError(
             'Ambiguous return value: Selected block contains assignment(s) to '
                 'local variables and return statement.');
         return result;
       }
       // prepare to return an assigned variable
       VariableElement returnVariable = assignedUsedVariables[0];
@@ skipping 97 matching lines @@
   }
 
   /**
    * Checks if [node] has a [MethodInvocation].
    */
   static bool _hasMethodInvocation(AstNode node) {
     var visitor = new _HasMethodInvocationVisitor();
     node.accept(visitor);
     return visitor.result;
   }
+
+  /**
+   * Returns `true` if the given [statement] may end with a [ReturnStatement].
+   */
+  static bool _mayEndWithReturnStatement(Statement statement) {
+    _HasReturnStatementVisitor visitor = new _HasReturnStatementVisitor();
+    statement.accept(visitor);
+    return visitor.hasReturn;
+  }
 }
 
 
 /**
  * [SelectionAnalyzer] for [ExtractMethodRefactoringImpl].
  */
 class _ExtractMethodAnalyzer extends StatementAnalyzer {
   _ExtractMethodAnalyzer(CompilationUnit unit, SourceRange selection)
       : super(unit, selection);
 
@@ skipping 147 matching lines @@
 class _HasMethodInvocationVisitor extends RecursiveAstVisitor {
   bool result = false;
 
   @override
   visitMethodInvocation(MethodInvocation node) {
     result = true;
   }
 }
 
 
+class _HasReturnStatementVisitor extends RecursiveAstVisitor {
+  bool hasReturn = false;
+
+  @override
+  visitBlockFunctionBody(BlockFunctionBody node) {
+  }
+
+  @override
+  visitReturnStatement(ReturnStatement node) {
+    hasReturn = true;
+  }
+}
+
+
 class _InitializeOccurrencesVisitor extends GeneralizingAstVisitor<Object> {
   final ExtractMethodRefactoringImpl ref;
   final _SourcePattern selectionPattern;
   final Map<String, String> patternToSelectionName;
 
   bool forceStatic = false;
 
   _InitializeOccurrencesVisitor(this.ref, this.selectionPattern,
       this.patternToSelectionName);
 
@@ skipping 87 matching lines @@
       // next statement
       if (found) {
         beginStatementIndex += selectionCount;
       } else {
         beginStatementIndex++;
       }
     }
   }
 }
 
-
 class _InitializeParametersVisitor extends GeneralizingAstVisitor<Object> {
   final ExtractMethodRefactoringImpl ref;
   final List<VariableElement> assignedUsedVariables;
 
   _InitializeParametersVisitor(this.ref, this.assignedUsedVariables);
 
   @override
   Object visitSimpleIdentifier(SimpleIdentifier node) {
     SourceRange nodeRange = rangeNode(node);
     if (ref.selectionRange.covers(nodeRange)) {
@@ skipping 38 matching lines @@
       }
       // remember declaration names
       if (node.inDeclarationContext()) {
         ref._usedNames.add(node.name);
       }
     }
     return null;
   }
 }
 
+
 class _IsUsedAfterSelectionVisitor extends GeneralizingAstVisitor {
   final ExtractMethodRefactoringImpl ref;
   final VariableElement element;
   bool result = false;
 
   _IsUsedAfterSelectionVisitor(this.ref, this.element);
 
   @override
   visitSimpleIdentifier(SimpleIdentifier node) {
     VariableElement nodeElement = getLocalVariableElement(node);
@@ skipping 103 matching lines @@
       return false;
     }
     for (int i = 0; i < parameterTypes.length; i++) {
       if (other.parameterTypes[i] != parameterTypes[i]) {
         return false;
       }
     }
     return true;
   }
 }