Re: [PATCH] patch-ids.c: cache patch IDs in a notes tree

[John Keeping <john@keeping.me.uk>]

On Sat, May 11, 2013 at 02:10:01PM -0700, Linus Torvalds wrote:
> On Sat, May 11, 2013 at 12:54 PM, John Keeping <john@keeping.me.uk> wrote:
> > This adds a new configuration variable "patchid.cacheRef" which controls
> > whether (and where) patch IDs will be cached in a notes tree.
> 
> Patch ID's aren't stable wrt different diff options, so I think this
> is potentially a very bad idea.

Hmm... I hadn't realised that.  Looking a bit closer, it looks like
init_patch_ids sets up its own diffopts so its not affected by the
command line (except for pathspecs which would be easy to check for).
Of course that still means it can be affected by settings in the user's
configuration.

It's a pity that this can't be done since it gives a significant
performance improvement for some tasks that I perform relatively
frequently.  Is there a reason patch IDs couldn't be generated using
fixed diff options?  Since there's no way to control it from the command
line it seems surprising that the results of "log --cherry" might be
different based on what's in your config.

That could go either way I suppose - is it useful to be able to change
patch IDs based on command line arguments or is it wrong that as we add
persistent diff settings to the configuration we've been silently
changing the behaviour of "git patch-id" and "git cherry".