The following invalid code snippet generates a bogus error message since
GCC 3.1:
#define foo - ## >>
foo;
bug.c:2:1: error: pasting "->" and ">>" does not give a valid preprocessing
token
bug.c:2: error: expected identifier or '(' before '->' token
The problem is that we tried to paste "-" and ">>" and not "->" and ">>".
GCC 3.0.x produced a correct diagnostic.

Comment #1 from mmitchel at gcc dot gnu dot org 2006-10-11 22:30
This patch is K, thanks.

Comment #2 from jakub at gcc dot gnu dot org 2006-10-12 09:26
Subject: Bug 28709

Author: jakub
Date: Thu 12 09:25:59 2006
New Revision: 117664

URL:
Log:
PR preprocessor/28709
* macro.c (paste_tokens): Do error reporting here, use BUF with the
spelled LHS token as opposed to spelling it again.
(paste_all_tokens): Don't report errors here, just break on failure.

* gcc.dg/cpp/paste14.c: New test.

Added:

Modified:
trunk/gcc/testsuite/ChangeLog
trunk/libcpp/ChangeLog
trunk/libcpp/macro.c

Comment #4 from tromey at gcc dot gnu dot org 2006-12-28 04:22
FWIW what happens here is that 'foo;' is turned into
'->>;' by cpp; then the second error is emitted by the
C parser. You can easily see this by comparing the -E output
against the output.

The problem here is that paste_tokens backs up over
the '>>' token, but it leaves the half-pasted '->' token
in *plhs. I have a fix that I'm testing.

Comment #5 from patchapp at dberlin dot org 2007-01-01 21:57
Subject: Bug number PR preprocessor/28709
A patch for this bug has been added to the patch tracker.
The mailing list url for the patch is

Comment #6 from gdr at gcc dot gnu dot org 2007-02-03 18:54
Won't fix in GCC-4.0.x. Adjusting milestone.

Comment #7 from ahs3 at fc dot hp dot com 2007-03-07 00:49
Is this code snippet related to this bug, or a new one entirely?

#define LABEL(a, b) a##b##:

int main () {
LABEL(all,done)
return 0;
}

If I compile it:

$ gcc -o foo.o foo.c
foo.c:4:1: error: pasting "alldone" and ":" does not give a valid preprocessing
token

However, if I use -E first, and compile the result, the snippet compiles
properly,

Comment #8 from pinskia at gcc dot gnu dot org 2007-03-07 00:58
(In reply to comment #7)
Is this code snippet related to this bug, or a new one entirely?
Actually the error message is fully correct in that case.

$ gcc -o foo.o foo.c
foo.c:4:1: error: pasting "alldone" and ":" does not give a valid preprocessing
token

However, if I use -E first, and compile the result, the snippet compiles
properly,

I don't, I get an error even with -E on the mainline, 3.3.5, and 4.0.2:
gcc t.c -E -o t.i
t.c:4:1: error: pasting "alldone" and ":" does not give a valid preprocessing
token

Comment #9 from ahs3 at fc dot hp dot com 2007-03-07 18:43
Ah, my fault; I wasn't being clear. I still get the error message with -E,
that is true. However, the resulting code from cpp I thought was correct -- it
just produces what I thought was a normal C label, and if I ignore the error
message, I can compile the output from -E just fine. It seems to me that if
cpp no longer recognizes ##, then the message should say so ('deprecated cpp
token', or something); if cpp does recognize ##, then I don't think the error
message should be produced at all since the resulting tokens ('alldone:') are
valid C source.

If none of those are the case, what bit of info am I not understanding? And
I'm still not sure this is the same bug as the original report -- it seems
similar, but let me know if it's something different entirely.

Thanks.

Comment #10 from pinskia at gcc dot gnu dot org 2007-03-07 21:39
(In reply to comment #9)
If none of those are the case, what bit of info am I not understanding?

Yes "alldone:" are really two seperate tokens in C :).
If you change the definition of LABEL to:
#define LABEL(a, b) a##b :

it works exactly the same as you want it to work.

And yes it is unrelated to this bug really.

Comment #11 from tromey at gcc dot gnu dot org 2007-04-25 01:29
Bug 31182 has been marked as a duplicate of this bug.

Comment #12 from tromey at gcc dot gnu dot org 2007-05-02 20:33
Subject: Bug 28709

Author: tromey
Date: Wed May 2 19:33:44 2007
New Revision: 124356

URL:
Log:
libcpp
PR preprocessor/28709:
* macro.c (paste_tokens): Remove PASTE_LEFT from the old lhs.
gcc/testsuite
PR preprocessor/28709:
* gcc.dg/cpp/pr28709.c: New file.

Added:

Modified:
trunk/gcc/testsuite/ChangeLog
trunk/libcpp/ChangeLog
trunk/libcpp/macro.c

Comment #13 from tromey at gcc dot gnu dot org 2007-05-02 20:34
I checked in the follow-up patch to the trunk.
So this fully works on 4.3.