Remove the module-level get_src_requirement().

[cjerdonek]

This is my last preparatory refactoring before posting a PR for issue #5031.

[cjerdonek]

This PR removes the module-level get_src_requirement() function inside pip's vcs module.

There are a number of reasons for this:

1. The function is used only once in the entire code base (in the get_requirement_info() method that this PR is modifying), so we have the ability to inline it.

2. Inlining the function lets us DRY up the calls to dist.as_requirement() to a single place, which we do in this PR.

3. Other than calling dist.as_requirement(), all the function does is add a logger.warning() call in a try-except.

4. Moving the logging call to get_requirement_info() lets us see how the logging call fits in with the rest of the logging calls inside get_requirement_info() and puts us in a position to remove duplicate or similar logging calls (there are such) and adjust the comments accordingly.

5. Inlining the function lets us combine the try-except block in get_src_requirement() with the try-except logic in get_requirement_info().

[pradyunsg]

I like the control flow changes here - they make things easier to follow and more readable.

[pradyunsg]

I don't think this needs to be a classmethod since it doesn't actually use cls. It can probably be a module level function.

[cjerdonek]

I don't think this needs to be a classmethod since it doesn't actually use cls. It can probably be a module level function.

@pradyunsg Good observation -- thanks! I've made that change.

When making that change, I noticed an additional simplification that can be made. Not only the cls argument, but also the dependency_links argument can be removed. This was made possible by PR #5869, but I didn't notice it then.

Does it still look okay to you now? Thanks again.

[cjerdonek]

Thanks, @pradyunsg and @xavfernandez!

[pradyunsg]

Post merge approval from me. :)