[llvm-dev] RFC: Dealing with out of tree changes and the LLVM git monorepo

[Mehdi AMINI via llvm-dev]

Le lun. 5 nov. 2018 à 07:43, David Greene <dag at cray.com> a écrit :

> Mehdi AMINI <joker.eph at gmail.com> writes:
>
> >     > If you want a monorepo view for all of your branches' histories
> >     > too it's more involved, but I'm not sure anyone really needs
> >     > that. In any case, even if someone does want that the nature of
> >     > the zipper approach means it could be done later
> >     > non-destructively.
> >
> >     That's true, but then they would suffer the same duplication of
> >     history that motivated you to create the zippered repository in
> >     the first place.
> >
> > It isn't clear to me why it would suffer from the same duplication of
> > history?
> > The duplication of history is only due to the *rewrite* of the git
> > hash between the individual repo and the monorepo.
> > If we were starting with a subtree merge and later add a "zipped"
> > history, we would only add the merges commit without rewriting
> > anything I think.
>
> I'm not sure how this after-the-fact merge would work.  How was the
> zippered monorepo history created?  Do a subtree merge of each
> subproject and then...?
>
> I was imagining someone taking their existing subproject repository tree
> and simply pushing their local branches to a clone of the zippered
> monorepo (ZMR).  So their commits would exist as branches off the ZMR's
> subproject histories.  To then get them merged into a "proper" monorepo
> history would require...<something>...to merge a subproject commit with
> an appropriate zippered commit to create a zippered local branch.
> That's effectively two commits for each local downstream subproject
> commit.


Yes, but that's the case for the zipper repo anyway: one merge per commit.
The point is that the second commit is just a trivial merge, it wouldn't
show up in a file `git log` for example.
In the linear rewritten monorepo, adding the history taken from the
existing git mirror would lead to duplicated commits, as in *identical*
commit / commit with the same diff but different git hashes. I'd expect git
log to show us the two commits in the git log of a single file.

-- 
Mehdi
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