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

Jeff King [off-list ref] 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.

quoted

 *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.