fix #25739, incorrectly expanding a generic comment multiple times

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

Index: pkg/analyzer/lib/src/generated/parser.dart
diff --git a/pkg/analyzer/lib/src/generated/parser.dart b/pkg/analyzer/lib/src/generated/parser.dart
index 7a39b047f1529df3d789f1a7f3a7410b8becf33b..c5933ee7245ca82118246af6a42aea7ad12cb621 100644
--- a/pkg/analyzer/lib/src/generated/parser.dart
+++ b/pkg/analyzer/lib/src/generated/parser.dart
@@ -3948,6 +3948,15 @@ class Parser {
           String comment = t.lexeme.substring(prefixLen, t.lexeme.length - 2);
           Token list = _scanGenericMethodComment(comment, t.offset + prefixLen);
           if (list != null) {
+            // Remove the tokens from the comment stream.
+            if (t.previous != null) {
+              t.previous.setNext(t.next);
+            } else {
+              assert(_currentToken.precedingComments == t);
+              // The implementation types all have this setter, but the Token
+              // interface does not.
+              (_currentToken as dynamic).precedingComments = t.next;

[Jennifer Messerly, 2016/02/10 19:15:07]

not enthused about this... suggestions? :)

[Bob Nystrom, 2016/02/12 17:40:47]

Yeah, this seems gross to me, but I don't know the parser well enough to suggest
an alternative.

When I was poking at this, I considered resynthesizing the token without the
comment, but that seemed like a lot of work too.

[Brian Wilkerson, 2016/02/12 17:56:55]

I just turned Token into an interface, and replaced it in the type hierarchy
with SimpleToken, which is clearly marked as internal implementation, so that
opens some options.

(1) We could add a setter to SimpleToken, although it would have to throw an
exception if the token cannot support comments.

(2) We could add an internal interface ("TokenWithComment"?), implement it in
all of the existing "*WithComment" classes, and add the setter there, which
would avoid the possibility of throwing an exception.

(3) We could define TokenWithComment as a simple class and mix it in to all of
the existing "*WithComment" classes.

+            }
             // Insert the tokens into the stream.
             _injectTokenList(list);
             return true;