Add visitors that throw by default

pkg/analyzer/lib/dart/element/element.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.
 
 /**
  * Defines the element model. The element model describes the semantic (as
  * opposed to syntactic) structure of Dart code. The syntactic structure of the
  * code is modeled by the [AST structure](../ast/ast.dart).
  *
  * The element model consists of two closely related kinds of objects: elements
@@ skipping 701 matching lines @@
    *
    * This method is expensive, because resolved AST might have been already
    * evicted from cache, so parsing and resolving will be performed.
    */
   CompilationUnit get unit;
 
   /**
    * Use the given [visitor] to visit this element. Return the value returned by
    * the visitor as a result of visiting this element.
    */
-  /*=T*/ accept/*<T>*/(ElementVisitor<dynamic/*=T*/> visitor);
+  /*=T*/ accept/*<T>*/(ElementVisitor<dynamic/*=T*/ > visitor);

[Paul Berry, 2017/01/09 17:36:51]

Unintentional change?

[Brian Wilkerson, 2017/01/09 18:08:07]

Yes. The formatter appears to be inserting it, but I don't know why because it
doesn't do so elsewhere. I manually removed it, but it might reappear the next
time the file is formatted.

[Paul Berry, 2017/01/09 18:17:56]

FYI, Bob: possible formatter bug.

[Bob Nystrom, 2017/01/11 01:19:38]

Hmm, yeah. It tries to handle most of the generic method comment stuff
correctly. (They are not formatted like regular /* */ comments in some ways.)
But it's not a heavily tested code path, and it's effectively deprecated now, so
I'm not inclined to improve it.

We have real syntax for generic methods. :)

[Paul Berry, 2017/01/11 04:17:09]

Fair enough.  Thanks for checking!

 
   /**
    * Return the documentation comment for this element as it appears in the
    * original source (complete with the beginning and ending delimiters), or
    * `null` if this element does not have a documentation comment associated
    * with it. This can be a long-running operation if the information needed to
    * access the comment is not cached.
    *
    * Throws [AnalysisException] if the documentation comment could not be
    * determined because the analysis could not be performed
@@ skipping 277 matching lines @@
   /**
    * Return an encoded representation of this location that can be used to
    * create a location that is equal to this location.
    */
   String get encoding;
 }
 
 /**
  * An object that can be used to visit an element structure.
  *
- * Clients may implement this class.
+ * Clients may not extend, implement or mix-in this class.
  */
 abstract class ElementVisitor<R> {
   R visitClassElement(ClassElement element);
 
   R visitCompilationUnitElement(CompilationUnitElement element);
 
   R visitConstructorElement(ConstructorElement element);
 
   R visitExportElement(ExportElement element);
 
@@ skipping 998 matching lines @@
   DartType get type;
 
   /**
    * Return a representation of the value of this variable, forcing the value
    * to be computed if it had not previously been computed, or `null` if either
    * this variable was not declared with the 'const' modifier or if the value of
    * this variable could not be computed because of errors.
    */
   DartObject computeConstantValue();
 }