Subject: Re: [PATCH v2 2/3] transport.c: introduce core.alternateRefsCommand

From: Taylor Blau <[email-masked]>
Date: Tue, 25 Sep 2018 18:06:06 -0700

On Fri, Sep 21, 2018 at 02:09:08PM -0700, Junio C Hamano wrote:
> Taylor Blau <[email-masked]> writes:
>
> > +core.alternateRefsCommand::
> > +	When listing references from an alternate (e.g., in the case of ".have"), use
>
> It is not clear how (e.g.,...) connects to what is said in the
> sentence.  "When advertising tips of available history from an
> alternate, use ..." without saying ".have" may be less cryptic.
>
> I dunno.

Thanks, I think that I tend to overuse both "e.g.," and "i.e.,". I took
your suggestion as above, which I think looks better than my original
prose.

> > +	the shell to execute the specified command instead of
> > +	linkgit:git-for-each-ref[1]. The first argument is the path of the alternate.
>
> "The path" meaning the absolute path?  Relative to the original
> object store?  Something else?

It's the absolute path, and I've updated the documentation to clarify it
as such.

> > +	Output must be of the form: `%(objectname) SPC %(refname)`.
> > ++
> > +This is useful when a repository only wishes to advertise some of its
> > +alternate's references as ".have"'s. For example, to only advertise branch
> > +heads, configure `core.alternateRefsCommand` to the path of a script which runs
> > +`git --git-dir="$1" for-each-ref refs/heads`.
> > +
> >  core.bare::
> >  	If true this repository is assumed to be 'bare' and has no
> >  	working directory associated with it.  If this is the case a
> > diff --git a/t/t5410-receive-pack.sh b/t/t5410-receive-pack.sh
> > new file mode 100755
> > index 0000000000..2f21f1cb8f
> > --- /dev/null
> > +++ b/t/t5410-receive-pack.sh
> > @@ -0,0 +1,54 @@
> > +#!/bin/sh
> > +
> > +test_description='git receive-pack test'
> > +
> > +. ./test-lib.sh
> > +
> > +test_expect_success 'setup' '
> > +	test_commit one &&
> > +	git update-ref refs/heads/a HEAD &&
> > +	test_commit two &&
> > +	git update-ref refs/heads/b HEAD &&
> > +	test_commit three &&
> > +	git update-ref refs/heads/c HEAD &&
> > +	git clone --bare . fork &&
> > +	git clone fork pusher &&
> > +	(
> > +		cd fork &&
> > +		git config receive.advertisealternates true &&
>
> Hmph.  Do we have code to support this configuration variable?

We don't ;-). Peff's explanation of why is accurate, and the mistake is
mine.

> > +		cat <<-EOF | git update-ref --stdin &&
>
> Style: writing "<<-\EOF" instead would allow readers' eyes to
> coast over without having to look for $variable_references in
> the here-doc.
>
> > +		delete refs/heads/a
> > +		delete refs/heads/b
> > +		delete refs/heads/c
> > +		delete refs/heads/master
> > +		delete refs/tags/one
> > +		delete refs/tags/two
> > +		delete refs/tags/three

Thanks, it ended up being much cleaner to write <<-\EOF, and avoid the
unnecessary cat(1) entirely.

> So, the original created one/two/three/a/b/c/master, fork is a bare
> clone of it and has all these things, and then you deleted all of
> these?  What does fork have after this is done?  HEAD that is
> dangling?
>
> > +		EOF
> > +		echo "../../.git/objects" >objects/info/alternates
>
> When viewed from fork/objects, ../../.git is the GIT_DIR of the
> primary test repository, so that is where we borrow objects from.
>
> If we pruned the objects from fork's object store before this echo,
> we would have an almost empty repository that borrows from its
> alternates everything, which may make a more realistic sample case,
> but because you are only focusing on the ref advertisement, it does
> not matter that your fork is full of duplicate objects that are
> available from the alternates.

I could go either way. You're right in that we have only a dangling HEAD
reference in the fork, and that all of the objects are still there. I
suppose that we could gc the objects that are there, but I think (as you
note above) that it doesn't make a huge difference either way.

> > +expect_haves () {
> > +	printf "%s .have\n" $(git rev-parse $@) >expect
>
> Quote $@ inside dq pair, like $(git rev-parse "$@").

Thanks, I fixed this (per your and Eric's suggestion), but ended up
removing the function entirely anyway.

> > +extract_haves () {
> > +	depacketize - | grep '\.have' | sed -e 's/\\0.*$//g'
> > +}
>
> Don't pipe grep into sed, especially when both the pattern to filter
> and the operation to perform are simple.
>
> I am not sure what you are trying to achive with 'g' in
> s/pattern$//g; The anchor at the rightmost end of the pattern makes
> sure that the pattern matches only once per line at the end anyway,
> so "do this howmanyever times as we have match on each line" would
> not make any difference, no?

I admit to not fully understanding when the trailing `/g` is and is not
useful. Anyway, I took Peff's suggestion below to convert this 'grep |
sed' pipeline into a Perl invocation, which I think ended up much
cleaner.

Thanks,
Taylor