making memctx more generally useful

[Christian Ebert]

* Steve Borho on Wednesday, January 02, 2013 at 14:31:01 -0600
> I am in the middle of adding a record-like hunk selection feature to the
> TortoiseHg commit tool; using a patch based memctx to avoid having to
> repeatedly re-write working copy files and potentially bungling the
> dirstate.
> 
> A problem that I have encountered (and based on a quick chat on IRC I am
> not the first) is that memctx.commit() directly calls into
> localrepo.commitctx() bypassing all the logic in localrepo.commit() which
> knows about subrepos, bookmarks, merge state, hooks, etc.
> 
> For the short term; I am duplicating the functionality of
> localrepo.commit() within my partial commit function, but it seems like
> there is a lot of room for improvement here to make the localrepo.commit()
> functionality more reachable.
> 
> Option #1 (minimal)
> 
> add an optional getcctxfn=context.workingctx argument to localrepo.commit()
> so callers can inject their own commit context callback; using the changes
> list and other arguments that localrepo.commit() discovers
> 
> Option #2
> 
> Move localrepo.commit() functionality into workingctx, make memctx derive
> from workingctx
> 
> Option #3
> 
> Split localrepo.commit() into multiple functions which can be called a la
> carte
> 
> Preferences?  Other options?

I always wanted to find a way to use memctx in the keyword
extension but could not and still cannot wrap my head around the
memctx concept.

Performance-wise it would probably most useful for update and
friends, but there I don't see how it could work because we need
to get the last change per file - a bit like hg log -l1 file. But
I might be utterly wrong in my understanding of memctx.

For commit I am quite certain that there must be a way to use it,
and perhaps even to make keyword cooperate with largefiles; see:
http://bz.selenic.com/show_bug.cgi?id=3550

c
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