gud breakage: ^done,changelist=[]

[Nick Roberts]

 > Anyone using gud from CVS?  It has been broken for me for quite some
 > time now, but it used to break `only' after about 100 prompts or so;
 > usually enough to nail the bug.

It can only help us if you report the bug when you first find it.

 > With current CVS (emacs -q), it breaks after less than 20 prompts when
 > debugging lilypond

There haven't been any significant changes in this code for the last three
months or so. Perhaps its breaking earlier because liypond has changed.
 
 >     M-x gdb
 >     gdb --annotate=2 lily/out/lilypond

That's odd because gud has used "--annotate=3" for over a year. However, it
shouldn't make any difference at the moment.

 ...
 >     (gdb) b main
 >     Breakpoint 1 at 0x81742a0: file main.cc, line 463.
 >     (gdb) r
 >     Starting program: 
 > /var/fred/cvs/savannah/lilypond/lilypond/lily/out/lilypond 
 >     [Thread debugging using libthread_db enabled]
 >     [New Thread 16384 (LWP 1314)]
 >     [Switching to Thread 16384 (LWP 1314)]

C++ and multithreaded, that might be pushing it a bit. If you don't use any
features of the new mode you can get the old behaviour using "gdb -fullname"
(read the debugger section in the Emacs manual).

 >     Breakpoint 1, main (argc=1, argv=0xbfffeb04) at main.cc:463
 >     (gdb) n
 > 
 > 17 times RET gives
 > 
 >     (gdb) 
 >     ^done,changelist=[]
 >     (gdb) 
 >     (gdb) list
 >     ^done,changelist=[]
 ...

It appears to have lost an annotation somewhere and can't recover. It is
probably the mode but it could also be that GDB fails to emit the right
annotation under this particular circumstance.

Please set the variable gdb-enable-debug-log (which records the transactions
between gdb and emacs) to t, trigger the bug and post the value of
gdb-debug-log to emacs-pretest-bugs.

Nick