[merge] Control-backspace to drop into the debugger

[Martin Pool]

On 4/17/07, Robert Collins <robertc at robertcollins.net> wrote:
> On Tue, 2007-04-17 at 15:16 +1000, Martin Pool wrote:
> >
> > That puts you into pdb if an error occurs.  This puts you in at any
> > time of your choosing.  They're different.
> >
> > I should maybe explain them in HACKING as well.
>
> Well if you do BZR_PDB=1 then hit ctrl-\, won't you be put into pdb ?

No, because sigquit just terminates Python.  It doesn't get turned
into an exception like sigint does.

You can set BZR_PDB and then press C-c, but then you're in postmortem
debugger mode, and the process is already shutting down. You can
continue but then the process terminates.

> I guess I'm wondering if its /desirable/ to have this hook active all th
> time.

Well the downsides are:

- Some more code is loaded unconditionally.  The change to bzr rocks
benchmark time seems to be in the noise.
- People may be confused if they hit C-\ accidentally.  I put the
message in to try to make it clear.
- Processes may get stuck if they're running noninteractively and get
a sigquit, but that shouldn't just randomly happen.

Personally I think it's quite useful to have always available.

John's very cool --profile-imports showed that I was loading pdb all
the time when it's not needed, so here's an updated bundle.

-- 
Martin
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