[llvm-dev] [RFC] One or many git repositories?

[Chandler Carruth via llvm-dev]

On Wed, Jul 20, 2016 at 6:02 PM Mehdi Amini via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

>
> > On Jul 20, 2016, at 5:56 PM, Renato Golin via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
> >
> > On 21 July 2016 at 01:39, Justin Lebar <jlebar at google.com> wrote:
> >> This is true if you s/checkout/clone/.  With a single repo, you must
> >> clone (download) everything (*), but after you've done so you can use
> >> sparse checkouts to check out (create a working copy of) only llvm and
> >> clang.  So you should only notice the fact that there exist things
> >> other than llvm and clang when you first clone (download) llvm.
> >
> > So, we use that to a certain extent.
> >
> > Linaro's GCC validation uses the full checkout, then do a shallow
> > checkout that only has the updates.
> >
> > Our LLVM scripts, OTOH, clone all repos and use worktree for *all*
> > branches, and we only branch on the repos that we choose, for each
> > "working dir".
> >
> > Our scripts probably would need certain modifications... but it should
> be fine.
> >
> > But I'm not, by far, the most problematic user.
> >
> > The real problem, and why people accepted sub-modules, is that a lot
> > of downstream people only use one or another projects. Mostly LLVM or
> > Clang or libc++.
> >
> > Checking out all of it is bad, but having them officially interlinked,
> > it seems, is worse. IIUC, the problem is that the projects are now
> > built independently on their projects, but more and more CMake changes
> > are creeping in, making it harder and harder to separate their
> > projects from the rest of LLVM. This means they'll now depend on a
> > much larger body of sources that will need to be compiled together,
> > and will probably mean they'll abandon LLVM in favour of something
> > lighter.
> >
> > I honestly don't know how big is that problem, I don't have it myself,
> > but I "can imagine" compiling LLVM and Clang without need would be
> > pretty bad.
>
>
> You seem to imply that all the projects in the single repo would be built
> by default, while it is not part of the proposal.
> Actually I’d expect an opt-in mechanism, so that: `mkdir build-llvm && cd
> build-llvm && cmake ../llvm` only builds LLVM.
>

If we end up with a single repository, I agree and think at least some
level of opt-in for building subprojects is essential.

I would expect at *most* to automatically enable building the set of
subprojects we currently suggest by default in the getting started docs.
Any more than that wouldn't make sense, and I could even imagine defaulting
*fewer* projects at the build system level.


>
> —
> Mehdi
>
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