Re: Segfault in git when using git logs

[Elijah Newren <newren@gmail.com>]

On Tue, Nov 3, 2020 at 3:21 AM Christian Couder
<christian.couder@gmail.com> wrote:
>
> On Tue, Nov 3, 2020 at 11:19 AM SZEDER Gábor <szeder.dev@gmail.com> wrote:
> >
> > On Mon, Nov 02, 2020 at 09:43:21AM -0500, Jeff King wrote:
>
> > > but I'm not clear on how "--follow" and "-L" are supposed to interact.
> >
> > They shouldn't, I would say.  Though it would be great if their
> > rename-following logic would be unified.  In particular, line-level
> > log does a better job at rename following in some ways, notably it can
> > track multiple files at once, while '--follow' can only handle a
> > single file.  So I think the rename following logic should be
> > extracted from 'line-log.c' and made more generic, and it should be
> > used to implement '--follow', removing some restrictions of the
> > latter, not to mention removing the duplicated logic.
> >
> > (This might be a good GSoC project, though some of Linus' remarks in
> > 750f7b668f (Finally implement "git log --follow", 2007-06-19) like
> > "you did have to know and understand the internal git diff generation
> > machinery pretty well, and had to really be able to follow how commit
> > generation interacts with generating patches and generating the log"
> > and "this patch does seem to be firmly in the core "Linus or Junio"
> > territory" are worrying...)
>
> Thanks for the suggestion!
>
> For the Outreachy round starting next December, we have proposed a
> project to accelerate rename detection and range-diff based on:
>
> https://github.com/gitgitgadget/git/issues/519
>
> I am not sure how much it is related to this though.

As worded, the project is only tangentially related.  If someone were
to plumb better rename following through, then this Outreachy project
might make the underlying internals faster, but that's it.  However,
it's a certainly an interesting related project.

Also, I'll note that there is some code coming with merge-ort that
should help write an improved --follow implementation, and, in fact,
was specially added with that goal in mind.  merge-ort adds to
diffcore-rename.c the ability to limit rename detection to either
relevant_sources (e.g. only consider removed filenames matching these
paths for rename detection) or relevant_targets (e.g. only include
added files matching these paths for rename detection), or both.  The
relevant_targets was not useful within the merge-ort implementation,
but since I was adding relevant_sources it seemed like a natural
pairing; I added it for completeness and was specifically thinking how
it would be useful for log --follow when I did so.  (I also think the
strmap API will also make it a bit easier to implement an improved
--follow.)  One of my goals was to use the relevant_targets ability as
part of an improved log --follow implementation after getting the rest
of the merge-ort stuff done, but it might be a useful intern project
instead.