Re: [RFC PATCH v4 2/3] Show the call history when an alias is looping

From: Jeff King <peff@peff.net>
Date: Sep 8, 2018, 16:29 UTC
Message-ID: <20180908162908.GC9016@sigill.intra.peff.net>
In-Reply-To: <CACsJy8C+VPGyu1D6yeFU3eqzwusv_Q=tobZgvXOtZ=5gYak5dg@mail.gmail.com>

On Sat, Sep 08, 2018 at 03:34:34PM +0200, Duy Nguyen wrote:

Show 13 quoted lines

> On Sat, Sep 8, 2018 at 12:44 AM Tim Schumacher <timschumi@gmx.de> wrote:
> >
> > Just printing the command that the user entered is not particularly
> > helpful when trying to find the alias that causes the loop.
> >
> > Print the history of substituted commands to help the user find the
> > offending alias. Mark the entrypoint of the loop with "<==" and the
> > last command (which looped back to the entrypoint) with "==>".
> 
> An even simpler way to give this information is simply suggest the
> user tries again with GIT_TRACE=1. All alias expansion is shown there
> and we teach the user about GIT_TRACE. But your approach is probably
> more user friendly.

Good point. I'm OK with the amount of code here for the nicer message (but would be happy either way).

If we were going to track cross-process loops like Ævar suggested, I think I'd rather go with a simple counter and just ask the user to run with GIT_TRACE when it exceeds some maximum sanity value. For two reasons:

  1. Passing a counter through the environment is way simpler than
     an arbitrarily-sized list.

  2. When you get into multiple processes, there's potentially more
     going on than just Git commands. You might have a git command which
     runs a hook which runs a third party script which runs a git
     command, which runs a hook, and so on. That full dump is going to
     be more useful.

-Peff