Docs feedback: Merge request search has undocumented filtration possibilities
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https://docs.gitlab.com/ee/api/search.html#scope-merge_requests-2
According to the documentation, you can only perform basic search upon `/api/v4/projects/6/merge_requests`. But it is in fact possible to search based on the source branch by using the key `source_branch` as a parameter (in place of `search`).
With reference to the documentation, an example request would be: `curl --header "PRIVATE-TOKEN: <your_access_token>" "https://gitlab.example.com/api/v4/projects/6/merge_requests/source_branch=jaja-test&target_branch=master"`
This functionality is very useful if you only have a branch name and want to discover the id of the merge request linked to it.
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