Re: [PATCH 2/2] xdiff: implement empty line chunk heuristic

[Jeff King <peff@peff.net>]

On Wed, Apr 20, 2016 at 09:09:53AM -0700, Junio C Hamano wrote:

> "Michael S. Tsirkin" <mst@redhat.com> writes:
> 
> > FWIW IIRC what that commit is about is ability to reorder the chunks in
> > a patch without changing patch-id. Not about keeping id stable across
> > git revisions.
> 
> OK, but "reorder the chunks" is not meant to stay to be the _ONLY_
> purpose for an option whose name is a broad "--[un]stable", but
> merely one (and only) possible cause of patch-id instability that
> happened to be noticed as an issue back then and was dealt with that
> commit, no?  In other words, the intent of the "--stable" feature is
> to give a stable ID that is not affected by random end-user settings
> (e.g. diff.orderfile) and if somebody invents a new configurable knob
> in the future, they are supposed to pay attention to the "--stable"
> feature or existing users who do use "--stable" will be broken, no?

I forgot that we added "--stable". Evne if it is not meant to be about
stability across versions, is there any reason _not_ to turn off
this heuristic for --stable (or for patch-ids in general)?

I guess maybe that creates some inconsistency between generating a
patch-id directly, and making one from a diff given on stdin (though I
don't know that we can promise much about the latter in the general
case; we can fix file ordering, but we don't have enough information to
tweak other aspects).

-Peff