[Distutils] What metadata does pip actually need about sdists?

[Marcus Smith]

> 2) after unpacking this sdist it then calls 'setup.py egg_info' to get
> the full metadata for the wheel


I wouldn't say "get the full metadata for the wheel".  it's not a wheel
yet.
`egg_info` run so we can use the pkg_resources api to find the dependencies.



> Specifically what it does with this is
> extract the setup_requires and install_requires fields


specifically, we call `requires` on pkg_resources distribution objects
https://github.com/pypa/pip/blob/develop/pip/req/req_set.py#L583



> 3) eventually it actually builds the package, and this produces a
> wheel (or wheel equivalent) that has its own metadata (which often
> matches the metadata from egg_info in step (2), but not always)
>

"not always"?  not following your point
they're 2 different formats, but should contain the same essential
information.
here's the wheel code that does the conversion
https://bitbucket.org/pypa/wheel/src/1cb7374c9ea4d5c82992f1d9b24cf7168ca87707/wheel/metadata.py?at=default&fileviewer=file-view-default#metadata.py-90



> name and version before it runs egg_info, I assume that what this
> means is that it's crucial for pip to have static access to dependency
> information?


yes



> It would be somewhat convenient if sdists did list their binary
> dependencies:


not sure about your insertion of "binary" here.
pip is concerned with finding python project dependencies (i.e. name and
version constraints) in the sdist
and then based on the current install environment, it will further
constrain the wheels chosen based on architecture and python implementation.
and to be perfectly clear, none of this deals with non-python OS/Distro
requirements.



> 3) if any of the packages-to-be-installed are sdists, then fetch them,
> run egg_info or build them or whatever to get their real dependencies,
> add these to the graph, and go to step 1
>

this is the pain we don't want in the future.

since we're simply talking about name/version constraints (not
platform/python), It's hard to conceive that we'd agree on an sdist spec
that didn't include that.



> Do the relevant pip maintainers
> even read this mailing list? :-)
>

I try  :  )
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