New NodeLocator which uses positions of characters, not between them.

R=brianwilkerson@google.com
BUG=

Review URL: https://codereview.chromium.org/1490933002 .

pkg/analyzer/lib/src/generated/ast.dart

@@ -12945,6 +12945,95 @@ class NodeLocator extends UnifyingAstVisitor<Object> {
   }
 }
 
+/**
+ * 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.
+ */
+class NodeLocator2 extends UnifyingAstVisitor<Object> {
+  /**
+   * The inclusive start offset of the range used to identify the node.
+   */
+  int _startOffset = 0;
+
+  /**
+   * The inclusive end offset of the range used to identify the node.
+   */
+  int _endOffset = 0;
+
+  /**
+   * The found node or `null` if there is no such node.
+   */
+  AstNode _foundNode;
+
+  /**
+   * Initialize a newly created locator to locate the deepest [AstNode] for
+   * which `node.offset <= [startOffset]` and `[endOffset] < node.end`.
+   *
+   * If [endOffset] is not provided, then it is considered the same as the
+   * given [startOffset].
+   */
+  NodeLocator2(int startOffset, [int endOffset])
+      : this._startOffset = startOffset,
+        this._endOffset = endOffset == null ? startOffset : endOffset;
+
+  /**
+   * 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) {
+      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) {
+    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;
+    }
+    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));
+    }
+    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.

pkg/analyzer/lib/src/task/dart.dart

@@ -2953,15 +2953,7 @@ abstract class InferStaticVariableTask extends ConstantEvaluationAnalysisTask {
    */
   VariableDeclaration getDeclaration(CompilationUnit unit) {
     VariableElement variable = target;
-    // Usually: Type ^name = ...
-    // Sometimes there is no space after the type: List<Type>^name = ...
-    // So, we need to use an offset within (or right after) the name:
-    //   Type n^ame =
-    //   List<Type>n^ame =
-    //   Type x^=
-    int searchOffset = variable.nameOffset + 1;
-    NodeLocator locator = new NodeLocator(searchOffset);
-    AstNode node = locator.searchWithin(unit);
+    AstNode node = new NodeLocator2(variable.nameOffset).searchWithin(unit);
     VariableDeclaration declaration =
         node.getAncestor((AstNode ancestor) => ancestor is VariableDeclaration);
     if (declaration == null || declaration.name != node) {

pkg/analyzer/test/generated/ast_test.dart

@@ -29,6 +29,7 @@ main() {
   runReflectiveTests(IndexExpressionTest);
   runReflectiveTests(NodeListTest);
   runReflectiveTests(NodeLocatorTest);
+  runReflectiveTests(NodeLocator2Test);
   runReflectiveTests(SimpleIdentifierTest);
   runReflectiveTests(SimpleStringLiteralTest);
   runReflectiveTests(StringInterpolationTest);
@@ -944,6 +945,50 @@ class NodeListTest extends EngineTestCase {
   }
 }
 
+@reflectiveTest
+class NodeLocator2Test extends ParserTestCase {
+  void test_onlyStartOffset() {
+    String code = ' int vv; ';
+    //             012345678
+    CompilationUnit unit = ParserTestCase.parseCompilationUnit(code);
+    TopLevelVariableDeclaration declaration = unit.declarations[0];
+    VariableDeclarationList variableList = declaration.variables;
+    Identifier typeName = variableList.type.name;
+    SimpleIdentifier varName = variableList.variables[0].name;
+    expect(new NodeLocator2(0).searchWithin(unit), same(unit));
+    expect(new NodeLocator2(1).searchWithin(unit), same(typeName));
+    expect(new NodeLocator2(2).searchWithin(unit), same(typeName));
+    expect(new NodeLocator2(3).searchWithin(unit), same(typeName));
+    expect(new NodeLocator2(4).searchWithin(unit), same(variableList));
+    expect(new NodeLocator2(5).searchWithin(unit), same(varName));
+    expect(new NodeLocator2(6).searchWithin(unit), same(varName));
+    expect(new NodeLocator2(7).searchWithin(unit), same(declaration));
+    expect(new NodeLocator2(8).searchWithin(unit), same(unit));
+    expect(new NodeLocator2(9).searchWithin(unit), isNull);
+    expect(new NodeLocator2(100).searchWithin(unit), isNull);
+  }
+
+  void test_startEndOffset() {
+    String code = ' int vv; ';
+    //             012345678
+    CompilationUnit unit = ParserTestCase.parseCompilationUnit(code);
+    TopLevelVariableDeclaration declaration = unit.declarations[0];
+    VariableDeclarationList variableList = declaration.variables;
+    Identifier typeName = variableList.type.name;
+    SimpleIdentifier varName = variableList.variables[0].name;
+    expect(new NodeLocator2(-1, 2).searchWithin(unit), isNull);
+    expect(new NodeLocator2(0, 2).searchWithin(unit), same(unit));
+    expect(new NodeLocator2(1, 2).searchWithin(unit), same(typeName));
+    expect(new NodeLocator2(1, 3).searchWithin(unit), same(typeName));
+    expect(new NodeLocator2(1, 4).searchWithin(unit), same(variableList));
+    expect(new NodeLocator2(5, 6).searchWithin(unit), same(varName));
+    expect(new NodeLocator2(5, 7).searchWithin(unit), same(declaration));
+    expect(new NodeLocator2(5, 8).searchWithin(unit), same(unit));
+    expect(new NodeLocator2(5, 100).searchWithin(unit), isNull);
+    expect(new NodeLocator2(100, 200).searchWithin(unit), isNull);
+  }
+}
+
 @reflectiveTest
 class NodeLocatorTest extends ParserTestCase {
   void test_range() {