Bug#1102278: coinstallation failure of various llvm-toolchain-20 packages

[Simon McVittie]

Control: tags -1 + patch

On Mon, 07 Apr 2025 at 09:44:53 +0200, Helmut Grohne wrote:
>[Various -dev packages] fail to coinstall despite explicitly declaring that
>capability via Multi-Arch: same. Most of them install
>architecture-dependent files to architecture-independent filenames below
>/usr/lib/llvm-20/lib. Please either move those files to multiarch
>locations or remove the Multi-Arch: same annotations.

There is a merge request from Bo YU at 
<https://salsa.debian.org/pkg-llvm-team/llvm-toolchain/-/merge_requests/164>, 
although it conflicts with subsequent changes to the 20 branch (only in 
the changelog entry, I think). Perhaps a maintainer or contributor could 
rebase it? Alternatively, Yuce Kurum's implementation of essentially the 
same thing from the 19 branch could be merged into 20.

I'm tagging this as "patch" even though there is not a 100% 
ready-to-apply patch for this, because the actual change (dropping 
Multi-Arch: same in several places) is quite simple.

The snapshot branch in git (clang 21 prereleases, not yet in Debian 
unstable or exerimental) will also need equivalent changes.

As a note to contributors, if a merge request adds a changelog entry, 
that guarantees that it will conflict with all other changes made at 
around the same time, so in my experience it is often better to write 
the text you would want to see in the changelog into the git commit 
message instead, something like this:

     Drop Multi-Arch: same from packages installing to non-multiarch paths

     Closes: #1102278

and then rely on the package's maintainer (or the non-maintainer DD 
preparing and signing a NMU) to run `gbp dch` before uploading. 
(But if that contradicts the LLVM maintainers' workflow, then please 
listen to them, not to me.)

     smcv