Contributes to rapidsai/build-planning#54.

The libraft-headers and libraft-headers-only conda packages are bundling rmm's headers. I believe that's because the librmm conda package isn't available in the libraft* conda build environment, and as a result it's getting rmm via CPM (thanks to rapids-cmake).

As a result, this project and any that depend on it are seeing warnings like the following in conda builds where conda's path_conflict setting is set to warn or prevent (like #2245):

This transaction has incompatible packages due to a shared path.
  packages: rapidsai-nightly/linux-64::librmm-24.04.00a38-cuda11_240326_ga98931b9_38, rapidsai-nightly/linux-64::libraft-headers-only-24.04.00a93-cuda11_240326_g9637b3c2_93
  path: 'include/rmm/mr/device/arena_memory_resource.hpp'

To fix that, this proposes the following changes:

• make librmm a host dependency of the following conda packages: libraft-headers-only, libraft-headers

Benefits of this change

• slightly smaller libraft-headers and libraft-headers-only conda packages
• reduced risk of runtime and installation issues caused by file clobbering

Notes for reviewers

History of changes to the librmm dependency for libraft-headers:

• both run and host: Adjusting conda packaging to remove duplicate dependencies #508
• both run and host, but ignoring its run_exports: Remove duplicate librmm runtime dependency #1264
• just run, but ignoring its run_exports: Remove extraneous host pinnings from libraft-headers-only. #2102

In particular, #2102 referred to the host dependency on librmm as "extraneous" but from a packaging perspective, I don't think it is. librmm being in host means it'll be present in the build environment, which means its headers will be found instead of downloaded, and therefore not packaging into the libraft* conda packages.

How I tested this

Built all the raft conda packages locally from branch-24.06 and confirmed that they contain rmm headers. Then again from this branch and confirmed they were gone.

docker run \
    --rm \
    --env-file "${PWD}/aws-creds.env" \
    -v $(pwd):/opt/work \
    -w /opt/work \
    -it rapidsai/ci-conda:cuda12.2.2-ubuntu22.04-py3.10-amd64 \
    bash

CI="true" \
  ci/build_cpp.sh

# On 'branch-24.06', this showed the rmm headers being packaged.
# On this branch, they're omitted.
tar --bzip2 -tf \
  /tmp/conda-bld-output/linux-64/libraft-headers-only-24.06.00a50-cuda12_240430_g1e0e2283_50.tar.bz2 \
| grep 'include/rmm' \
| wc -l

Also checked the CI logs from conda-cpp-build jobs here. On other recent PRs, I see CPM downloading rmm ...

-- CPM: Adding package [email protected] (branch-24.06)

... and all the rmm headers getting installed as part of the libraft-headers package

-- Installing: /opt/conda/conda-bld/_h_env_placehold_placehold_..._placeho/include/rmm/cuda_stream.hpp

(build link)

Here, I see librmm coming through via the conda package requirements ...

The following NEW packages will be INSTALLED:
    ...
    librmm:                      24.06.00a17-cuda12_240430_g26fa9ecb_17 rapidsai-nightly

... and being used instead of downloads via CPM ...

-- CPM: Using local package [email protected]

... and no installation of the rmm headers as part of building any libraft packages.

(build link)