Check whether we have a result instead of throwing an exception in NodeLocator.

pkg/analyzer/lib/src/dart/ast/utilities.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 analyzer.src.dart.ast.utilities;
 
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
@@ skipping 3672 matching lines @@
    * Search within the given AST [node] for an identifier representing an
    * element in the specified source range. Return the element that was found,
    * or `null` if no element was found.
    */
   AstNode searchWithin(AstNode node) {
     if (node == null) {
       return null;
     }
     try {
       node.accept(this);
-    } on NodeLocator_NodeFoundException {
-      // A node with the right source position was found.
     } catch (exception, stackTrace) {
       AnalysisEngine.instance.logger.logInformation(
           "Unable to locate element at offset ($_startOffset - $_endOffset)",
           new CaughtException(exception, stackTrace));
       return null;
     }
     return _foundNode;
   }
 
   @override
   Object visitNode(AstNode node) {
+    // Don't visit a new tree if the result has been already found.
+    if (_foundNode != null) {
+      return null;
+    }
+    // Check whether the current node covers the selection.
     Token beginToken = node.beginToken;
     Token endToken = node.endToken;
     // Don't include synthetic tokens.
     while (endToken != beginToken) {
       if (endToken.type == TokenType.EOF || !endToken.isSynthetic) {
         break;
       }
       endToken = endToken.previous;
     }
     int end = endToken.end;
     int start = node.offset;
     if (end < _startOffset) {
       return null;
     }
     if (start > _endOffset) {
       return null;
     }
+    // Check children.
     try {
       node.visitChildren(this);
-    } on NodeLocator_NodeFoundException {
-      rethrow;
     } catch (exception, stackTrace) {
       // Ignore the exception and proceed in order to visit the rest of the
       // structure.
       AnalysisEngine.instance.logger.logInformation(
           "Exception caught while traversing an AST structure.",
           new CaughtException(exception, stackTrace));
     }
+    // Found a child.
+    if (_foundNode != null) {
+      return null;
+    }
+    // Check this node.
     if (start <= _startOffset && _endOffset <= end) {
       _foundNode = node;
-      throw new NodeLocator_NodeFoundException();
     }
     return null;
   }
 }
 
 /**
  * An object used to locate the [AstNode] associated with a source range.
  * More specifically, they will return the deepest [AstNode] which completely
  * encompasses the specified range.
  */
@@ skipping 27 matching lines @@
   /**
    * Search within the given AST [node] and return the node that was found,
    * or `null` if no node was found.
    */
   AstNode searchWithin(AstNode node) {
     if (node == null) {
       return null;
     }
     try {
       node.accept(this);
-    } on NodeLocator_NodeFoundException {} catch (exception, stackTrace) {
+    } catch (exception, stackTrace) {
       AnalysisEngine.instance.logger.logInformation(
           "Unable to locate element at offset ($_startOffset - $_endOffset)",
           new CaughtException(exception, stackTrace));
       return null;
     }
     return _foundNode;
   }
 
   @override
   Object visitNode(AstNode node) {
+    // Don't visit a new tree if the result has been already found.
+    if (_foundNode != null) {
+      return null;
+    }
+    // Check whether the current node covers the selection.
     Token beginToken = node.beginToken;
     Token endToken = node.endToken;
     // Don't include synthetic tokens.
     while (endToken != beginToken) {
       if (endToken.type == TokenType.EOF || !endToken.isSynthetic) {
         break;
       }
       endToken = endToken.previous;
     }
     int end = endToken.end;
     int start = node.offset;
     if (end <= _startOffset) {
       return null;
     }
     if (start > _endOffset) {
       return null;
     }
+    // Check children.
     try {
       node.visitChildren(this);
-    } on NodeLocator_NodeFoundException {
-      rethrow;
     } catch (exception, stackTrace) {
       // Ignore the exception and proceed in order to visit the rest of the
       // structure.
       AnalysisEngine.instance.logger.logInformation(
           "Exception caught while traversing an AST structure.",
           new CaughtException(exception, stackTrace));
     }
+    // Found a child.
+    if (_foundNode != null) {
+      return null;
+    }
+    // Check this node.
     if (start <= _startOffset && _endOffset < end) {
       _foundNode = node;
-      throw new NodeLocator_NodeFoundException();
     }
     return null;
   }
 }
 
 /**
- * An exception used by [NodeLocator] to cancel visiting after a node has been
- * found.
- */
-class NodeLocator_NodeFoundException extends RuntimeException {}
-
-/**
  * An object that will replace one child node in an AST node with another node.
  */
 class NodeReplacer implements AstVisitor<bool> {
   /**
    * The node being replaced.
    */
   final AstNode _oldNode;
 
   /**
    * The node that is replacing the old node.
@@ skipping 3919 matching lines @@
    * Safely visit the given [token], printing the [suffix] after the token if it
    * is non-`null`.
    */
   void _visitTokenWithSuffix(Token token, String suffix) {
     if (token != null) {
       _writer.print(token.lexeme);
       _writer.print(suffix);
     }
   }
 }