pip install farm-haystack[all-gpu] installs faiss-cpu, breaking FAISS

[ZanSara]

Describe the bug

• Installing Haystack with all GPU dependencies with pip install farm-haystack[all-gpu] will install also faiss-cpu, which does not play well with faiss-gpu. This should not happen.
• If the two are installed together, there seems to be a difficulty in using faiss-gpu: for example, faiss.get_num_gpus() returns 0.

Investigation results

• The issue was investigated with pipdeptree.
• The issue seems to come from the beir package, which requires faiss-cpu explicitly but is installed in the all-gpu group.
• Unfortunately, installing beir in all-gpu makes sense, because it's a benchmarking package.

Action to take

• Raise an issue on beir regarding their management of the FAISS dependency
• On the dependency faiss beir-cellar/beir#71
• Maybe we could consider volunteering to fix it

To Reproduce

• In a fresh Python env: pip install farm-haystack[all-gpu]
  • Note: this issue does not happen when doing pip install farm-haystack[faiss-gpu]

Error message

> pip freeze | grep faiss
faiss-cpu==1.7.2
faiss-gpu==1.7.2

Expected behavior

> pip freeze | grep faiss
faiss-gpu==1.7.2

Additional context

• https://discord.com/channels/993534733298450452/1019114526454595594

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