bug#67062: 30.0.50; [PATCH] Abbreviate the revision in 'vc-annotate' (for Git)

[Jim Porter]

On 12/14/2023 1:58 PM, Dmitry Gutov wrote:
> Do we need this option? I'm probably missing something, but IIUC a new 
> variable to control the behavior was suggested as an alternative to 
> using a new backend action. But here we add a new backend action anyway.

I had originally tried to do this purely with adding some variables and 
then using the existing backend functions. However, that would have 
resulted in 'vc-working-revision' returning either the full Git SHA or 
the short form depending on those options.

I didn't think that would be a safe idea, since a) other callers of 
'vc-working-revision' might not be prepared to handle short Git SHAs, 
and b) 'vc-working-revision' caches the revision, so it's not as easy as 
just setting a variable that controls the behavior: you'd need some 
special logic for invalidating the cache, or perhaps ignoring the cache 
when 'vc-use-short-revisions' is non-nil or something. All of those 
issues scared me enough that I wanted to avoid altering the behavior of 
'vc-working-revision' in any way.

While this patch does add a new backend action, it's purely optional and 
no other backend needs to be aware of it at all. I suppose I could 
hardcode the Git behavior in 'vc-short-revision', but that didn't seem 
to me to have any benefits over this version.