Re: [gentoo-dev] [RFC] Introducing LLVM_TARGET

[Sam James <sam@gentoo.org>]

Michał Górny <mgorny@gentoo.org> writes:

> [[PGP Signed Part:Undecided]]
> Hi,
>
> TL;DR: Given that (not really surprising) the current approach for LLVM
> dependencies doesn't work, I think it's time to give up and introduce
> LLVM_TARGETS.  This would probably mean introduce llvm-r1.eclass.
>
> However, since random apps tend to require old versions of LLVM, I do
> wonder if we should set the default value globally, or have the eclass
> generate IUSE defaults, so that everything works out of the box.
>

I need to think about this bit.

>
> The problem roughly is that right now we rely on depstrings like:
>
> DEPEND="
>   <sys-devel/clang-19:=
>   <sys-devel/llvm-19:=
>   || (
>     ( sys-devel/clang:18 sys-devel/llvm:18 )
>     ( sys-devel/clang:17 sys-devel/llvm:17 )
>     ( sys-devel/clang:16 sys-devel/llvm:16 )
>   )
> "
>
> This kinda works, in the sense that it will enforce that you have
> a single matching version of LLVM+Clang, and the eclass will use it. 
> However, the := deps on top may be entirely mismatched.  For example, if
> you have llvm:18 and clang:17 (+ llvm:17) installed, you'd get:
>
>   sys-devel/clang:17=
>   sys-devel/llvm:18=
>
> When more packages land on the list, this could lead to quite a mess.
>
> So what'd we go for would effectively be:
>
> DEPEND="
>   llvm_target_16? ( sys-devel/clang:16 sys-devel/llvm:16 )
>   llvm_target_17? ( sys-devel/clang:17 sys-devel/llvm:17 )
>   llvm_target_18? ( sys-devel/clang:18 sys-devel/llvm:18 )
> "
>
> WDYT?

We should mention that https://bugs.gentoo.org/923228 was the motivation
that tipped us over the edge here.

We should also consider the https://bugs.gentoo.org/880671 /
https://bugs.gentoo.org/821955 case, as I think this is going to end up
solving that too, actually.

But yeah, I like it. It solves a request we've had from users for a
while ("let me choose") and it solves these silly dep games.

Thank you!