Re: [PATCH 1/2] add setup step to filter-branch

[Junio C Hamano <gitster@pobox.com>]

Jeff King <peff@peff.net> writes:

> I have a feeling that if we were ever to rewrite filter-branch, it would
> probably be worth allowing people to write snippets in a better language
> (possibly even a domain-specific language). I'm sure that most of the
> program being written in shell doesn't help, but if we're spawning one
> or more shell instances per commit (plus the Git programs they spawn!),
> it's always going to be slow.
>
> But I suspect that would be an uphill battle, as our only stable API
> involves starting external processes anyway. You'd probably do better to
> pick a language you like and rewrite it in using libgit2's bindings to
> that language. It's not feature complete, but basic stuff like "put this
> entry in the tree" is certainly mature.
>
>>  *1* The issue is *not* that these individual filter commands expect
>>      <command> written as a shell scriptlet; it is that these
>>      scriptlets expect to be evaled inside a single shell process,
>>      making an update to a shell variable in one command visible to
>>      the next command that runs.
>
> I think you'd need a shell "helper" that's a single long-running process
> and just reads "eval the index snippet now" instructions from the C
> controller. At which point I don't think Andreas's "setup" feature is
> any harder to support. We just send an "eval the setup snippet"
> instruction first.

Yes.  I do not think this particular one makes things any worse than
it already is.  As I said, I do not have a strong opinion against
the topic; as long as people find the feature useful, I do not mind
applying it.

Thanks.