Add visitors that throw by default

pkg/analyzer/lib/dart/element/element.dart

Index: pkg/analyzer/lib/dart/element/element.dart
diff --git a/pkg/analyzer/lib/dart/element/element.dart b/pkg/analyzer/lib/dart/element/element.dart
index c235ea3e60a1de32c1bd7caee9e0592378b410f0..34853d07d5088fe6f8d5711bfe40f0bbe524ad68 100644
--- a/pkg/analyzer/lib/dart/element/element.dart
+++ b/pkg/analyzer/lib/dart/element/element.dart
@@ -719,7 +719,7 @@ abstract class Element implements AnalysisTarget, ResolutionTarget {
    * 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
@@ -1017,7 +1017,7 @@ abstract class ElementLocation {
 /**
  * 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);