Bug#1115227: libllvm19: Installing libllvm19:i386 on a AMD64 system with libllvm19 already installed will force apt to remove libllvm19 and dependent packages.

[Simon McVittie]

Control: forcemerge 1115227 1115194

On Mon, 15 Sep 2025 at 11:58:26 +0000, Sylvestre Ledru wrote:
>In general, it would be nice to add tests in:
>
>[2]https://salsa.debian.org/pkg-llvm-team/llvm-toolchain/-/blob/snapshot/debian
>/qualify-clang.sh?ref_type=heads
>
>to make sure these features don't regress. 
>(it can be as simple as looking at the dpkg output if the right fields are
>present)

I'll put it on my list, but it's a very long list, so please don't 
assume I'll get there any time soon!

How is this test run? Is it an autopkgtest, or do maintainers run it 
manually, or both, or what?

Ideally the test for multiarch co-installability would genuinely 
co-install amd64 and i386 packages to make sure it still works, but the 
autopkgtest infrastructure doesn't make that particularly 
straightforward. nss-mdns has a couple of tests that do co-install 
packages, such as 
<https://salsa.debian.org/debian/nss-mdns/-/blob/debian/master/debian/tests/multiarch-remove?ref_type=heads>.

>Should I just revert ? 
>
>[3]https://salsa.debian.org/pkg-llvm-team/llvm-toolchain/-/commit/fb68d9241f1338333cf5260136378e4a7ef43308

No, some of that commit was genuinely fixing RC bugs - for example 
libmlir- at LLVM_VERSION@ wasn't co-installable, because all architectures' 
instances of it install /usr/lib/llvm-19/lib/libMLIR.so.19.1 or similar, 
so having Multi-Arch: Same on libmlir-19 was a RC bug.

The goal is that each package should have Multi-Arch: same if and only 
if it doesn't collide with other architectures' instances of the same 
package. Normally this means that libraries in 
/usr/lib/${DEB_HOST_MULTIARCH} should be Multi-Arch: same, but 
everything in /usr/lib/llvm-19 should not. libllvm19 is in the first 
category, libmlir-19 is in the second, and I don't know which of the 
other library packages fit where.

There is a longer analysis in https://bugs.debian.org/1115194 indicating 
that this might have been partially caused by a `git cherry-pick` doing 
fuzzy matching between different packages' d/control stanzas - the list 
of packages that are M-A: same or 

Ideally /usr/lib/llvm-19 would split into 
/usr/lib/${DEB_HOST_MULTIARCH}/llvm-19 (#1111182) but that's a larger 
and more complicated request and should probably be postponed until 
after the more immediate problem is fixed.

     smcv