Re: [PATCH 3/3] builtin/commit-graph.c: support '--input=none'

[Taylor Blau <me@ttaylorr.com>]

On Fri, Jan 31, 2020 at 08:45:59PM +0100, Martin Ågren wrote:
> On Fri, 31 Jan 2020 at 01:30, Taylor Blau <me@ttaylorr.com> wrote:
> > In the previous commit, we introduced '--[no-]merge', and alluded to the
> > fact that '--merge' would be useful for callers who wish to always
> > trigger a merge of an incremental chain.
>
> Hmmm. So it looks like you've already had similar thoughts as I did
> about patch 1/3. At some point, you had a separate `--merge=...` option,
> then later made that `--split=...`. :-) Could you say something about why
> you changed your mind?

Heh :-). Left overs from an earlier version of this series. I think that
I already talked about why this was changed further up in the thread.

> > There is a problem with the above approach, which is that there is no
> > way to specify to the commit-graph builtin that a caller only wants to
> > include commits already in the graph. One can specify '--input=append'
> > to include all commits in the existing graphs, but the absence of
> > '--input=stdin-{commits,packs}' causes the builtin to call
> > 'fill_oids_from_all_packs()'.
>
> (Use one of those options with an empty stdin? Anyway, let's read on.)
>
> > Passing '--input=reachable' (as in 'git commit-graph write
> > --split=merge-all --input=reachable --input=append') works around this
> > issue by making '--input=reachable' effectively a no-op, but this can be
> > prohibitively expensive in large repositories, making it an undesirable
> > choice for some users.
> >
> > Teach '--input=none' as an option to behave as if '--input=append' were
> > given, but to consider no other sources in addition.
>
> `--input=none` almost makes me wonder if it should produce an empty
> commit-graph. But there wouldn't be much point in that... I guess
> another way of defining this would be that it "uses no input, and
> implies `--append`".

I suppose, although (like you) I can't imagine why anybody would want to
do that.

> > This, in conjunction with the option introduced in the previous patch
> > offers the convenient way to force the commit-graph machinery to
> > condense a chain of incrementals without requiring any new commits:
> >
> >   $ git commit-graph write --split=merge-all --input=none
>
> Right.
>
> > --- a/Documentation/git-commit-graph.txt
> > +++ b/Documentation/git-commit-graph.txt
> > @@ -39,24 +39,29 @@ COMMANDS
> >  --------
> >  'write'::
> >
> > -Write a commit-graph file based on the commits found in packfiles.
> > +Write a commit-graph file based on the commits specified:
> > +* With the `--input=stdin-packs` option, generate the new commit graph
> > +by walking objects only in the specified pack-indexes. (Cannot be
> > +combined with `--input=stdin-commits` or `--input=reachable`.)
> >  +
> > -With the `--input=stdin-packs` option, generate the new commit graph by
> > -walking objects only in the specified pack-indexes. (Cannot be combined
> > -with `--input=stdin-commits` or `--input=reachable`.)
> > -+
> > -With the `--input=stdin-commits` option, generate the new commit graph
> > +* With the `--input=stdin-commits` option, generate the new commit graph
> >  by walking commits starting at the commits specified in stdin as a list
> >  of OIDs in hex, one OID per line. (Cannot be combined with
> >  `--input=stdin-packs` or `--input=reachable`.)
> >  +
> > -With the `--input=reachable` option, generate the new commit graph by
> > +* With the `--input=reachable` option, generate the new commit graph by
> >  walking commits starting at all refs. (Cannot be combined with
> >  `--input=stdin-commits` or `--input=stdin-packs`.)
> >  +
> > -With the `--input=append` option, include all commits that are present
> > +* With the `--input=append` option, include all commits that are present
> >  in the existing commit-graph file.
>
> Do these changes above really belong in this commit?

I think so. My thought here was to leave this documentation as-is until
this patch, when adding '--input=none' would... somehow change this, but
trying to construct a reply, I can't seem to come up with why I thought
that this was a good idea in the first place ;-).

> > +* With the `--input=none` option, behave as if `input=append` were
> > +given, but do not walk other packs to find additional commits.
> > +
> > +If none of the above options are given, then commits found in
> > +packfiles are specified.
>
> "specified"? Plus, that also happens for `--input=append` right? (It
> really seems like "append" is an odd one among all the inputs.)

I reworded this slightly to not use "specified", which I agree is indeed
weird.

>
> >         N_("git commit-graph write [--object-dir <objdir>] [--append] "
> > -          "[--split[=<strategy>]] [--input=<reachable|stdin-packs|stdin-commits>] "
> > +          "[--split[=<strategy>]] "
> > +          "[--input=<reachable|stdin-packs|stdin-commits|none>] "
> >            "[--[no-]progress] <split options>"),
>
> Hmm, you've left "--append" the old way.

Fixed, and thanks for noticing.
>
> Martin

Thanks,
Taylor