The following invalid code snippet triggers an ICE since GCC 4.0.1:
template<intunion A;
struct A;
bug.cc:2: error: redeclaration of 'A<<anonymous>' as a non-template
bug.cc:2: internal compiler error: tree check: expected class 'type', have
'exceptional' (error_mark) in xref_tag, at cp/decl.c:9670
Please submit a full bug report, [etc.]

Comment #1 from reichelt at gcc dot gnu dot org 2006-08-14 08:30
Testing a patch.

Comment #2 from patchapp at dberlin dot org 2006-08-15 00:45
Subject: Bug number PR c++/28710
A patch for this bug has been added to the patch tracker.
The mailing list url for the patch is

Comment #3 from pinskia at gcc dot gnu dot org 2006-08-16 05:41
Confirmed.

Comment #4 from reichelt at gcc dot gnu dot org 2006-08-17 08:06
Subject: Bug 28710

Author: reichelt
Date: Thu Aug 17 08:06:27 2006
New Revision: 116211

URL:
Log:
PR c++/28710
* decl.c (xref_tag): Improve error message. Return early on error.

* gdg/template/redecl4.C: New test.

Added:

Modified:
trunk/gcc/cp/ChangeLog
trunk/gcc/cp/decl.c
trunk/gcc/testsuite/ChangeLog

Comment #5 from reichelt at gcc dot gnu dot org 2006-08-17 08:12
Subject: Bug 28710

Author: reichelt
Date: Thu Aug 17 08:12:00 2006
New Revision: 116212

URL:
Log:
PR c++/28710
* decl.c (xref_tag): Improve error message. Return early on error.

* gdg/template/redecl4.C: New test.

Added:

Modified:

Comment #5 from reichelt at gcc dot gnu dot org 2006-08-17 08:12
Subject: Bug 28710

Author: reichelt
Date: Thu Aug 17 08:12:00 2006
New Revision: 116212

URL:
Log:
PR c++/28710
* decl.c (xref_tag): Improve error message. Return early on error.

* gdg/template/redecl4.C: New test.

Added:

Modified:

Comment #6 from reichelt at gcc dot gnu dot org 2006-08-17 08:55
Subject: Bug 28710

Author: reichelt
Date: Thu Aug 17 08:55:17 2006
New Revision: 116216

URL:
Log:
PR c++/28710
* decl.c (xref_tag): Improve error message. Return early on error.

* gdg/template/redecl4.C: New test.

Added:

Modified:

Comment #7 from reichelt at gcc dot gnu dot org 2006-08-17 08:57
Fixed on mainline, 4.1 branch, and 4.0 branch.