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Subject: [gentoo-dev] [RFC] Introducing LLVM_TARGET
From: =?UTF-8?Q?Micha=C5=82_G=C3=B3rny?= <mgorny@gentoo.org>
To: gentoo-dev@lists.gentoo.org
Date: Mon, 05 Feb 2024 18:07:00 +0100
Organization: Gentoo
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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.


The problem roughly is that right now we rely on depstrings like:

DEPEND=3D"
  <sys-devel/clang-19:=3D
  <sys-devel/llvm-19:=3D
  || (
    ( 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.=20
However, the :=3D 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=3D
  sys-devel/llvm:18=3D

When more packages land on the list, this could lead to quite a mess.

So what'd we go for would effectively be:

DEPEND=3D"
  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?

--=20
Best regards,
Micha=C5=82 G=C3=B3rny


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