feat: Add CohereRanker for 2.0

[AnushreeBannadabhavi]

Related Issues

• Fixes CohereRanker haystack-core-integrations#645

Proposed Changes:

Add CohereRanker for Haystack 2.0.
Performs reranking of documents using Cohere reranking models. Reranks retrieved documents based on semantic relevance to a query.
For more information refer to Cohere reranker

How did you test it?

• Tests have been added in test_cohere.py
• Tested the component usage in a pipeline using the following code:

from haystack import Document, Pipeline
from haystack.document_stores.in_memory import InMemoryDocumentStore
from haystack.components.retrievers.in_memory import InMemoryBM25Retriever
from haystack.components.rankers import CohereRanker

# Note set your API key by running the below command in your terminal
# export CO_API_KEY="<your key>"

docs = [Document(content="Paris is in France"), 
        Document(content="Berlin is in Germany"),
        Document(content="Lyon is in France")]
document_store = InMemoryDocumentStore()
document_store.write_documents(docs)

retriever = InMemoryBM25Retriever(document_store = document_store)
ranker = CohereRanker(model="rerank-english-v2.0", top_k=3)

document_ranker_pipeline = Pipeline()
document_ranker_pipeline.add_component(instance=retriever, name="retriever")
document_ranker_pipeline.add_component(instance=ranker, name="ranker")

document_ranker_pipeline.connect("retriever.documents", "ranker.documents")

query = "Cities in France"
res = document_ranker_pipeline.run(data={"retriever": {"query": query, "top_k": 3}, 
                                   "ranker": {"query": query, "top_k": 2}})
print(res)

Notes for the reviewer

• When the list of documents to rerank is empty, Cohere raises an ApiError with the message invalid request: list of documents must not be empty.

raise ApiError(status_code=_response.status_code, body=_response_json)
cohere.core.api_error.ApiError: status_code: 400, body: {'message': 'invalid request: list of documents must not be empty'}

• The current implementation does not handle the empty document list scenario in CohereRanker since the exception raised by cohere is descriptive. However, I can add a check in the CohereRanker itself to handle such a scenario.

Checklist

• I have read the contributors guidelines and the code of conduct
• I have updated the related issue with new insights and changes
• I added unit tests and updated the docstrings
• I've used one of the conventional commit types for my PR title: fix:, feat:, build:, chore:, ci:, docs:, style:, refactor:, perf:, test:.
• I documented my code
• I ran pre-commit hooks and fixed any issue

[coveralls]

Pull Request Test Coverage Report for Build 8501345442

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.05%) to 89.584%

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Totals
Change from base Build 8466615213:	0.05%
Covered Lines:	5616
Relevant Lines:	6269

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💛 - Coveralls

[AnushreeBannadabhavi]

Hi @anakin87 and @dfokina!
I added "cohere==5.1.7" under dependencies in pyproject.toml (7fbe9bf) which causes the CI to fail due to a license issue. On the Cohere repo, it is mentioned that the license is MIT license. I'm not sure why the license compliance fails.

Previously, I included "cohere==5.1.7" under extra-dependencies in [tool.hatch.envs.test] and the license compliance was successful. However, this resulted in a different error where the test_for_missing_dependencies() test in test_imports.py failed.

I think I'm not adding cohere in the right place in pyproject.toml. It'd be great if you can provide some feedback here. Thank you!

[anakin87]

Hey, @AnushreeBannadabhavi!

Thank you for your contribution.

Starting from Haystack 2.0, the integrations maintained by us live here: https://github.com/deepset-ai/haystack-core-integrations

So, I would ask you to close this PR and open a similar one in the haystack-core-integrations repository, following these guidelines.

Feel free to ask for clarification (if needed).

[AnushreeBannadabhavi]

Thanks @anakin87! Will open a PR in https://github.com/deepset-ai/haystack-core-integrations shortly

[anakin87]

I will close this one and wait for the other 💙