Regression: sdists no longer install package data correctly with 35.0.0

Problem description

I have a package that uses setuptools_scm and include_package_data=True to include some Django templates and static files.

With setuptools 34.4.1, installing an sdist will install these package data files without any problems. However, with setuptools 35.0.0, installing the same sdist file will no longer install these package data files.

Note:

• Only installing sdists seem to be affected by this problem. In particular:
  • Generating sdists seems unaffected: both setuptools 34 and 35 generate sdists with the same (correct) distribution content and SOURCES.txt.
  • Installing sdists previously generated with either setuptools version works correctly with 34.4.1, and fails with 35.0.0.
• Wheels seem to be unaffected by this, and build and install fine with both setuptools 34 and 35.

Cause?

As far as I can tell, this regression is due to #436 / #1014, which no longer reads the sdist package’s existing manifest. When the manifest gets regenerated (?), the files that were previously included by setuptools_scm while building the sdist are no longer included anymore.

[jaraco]

Well, now we know. The quick fix is to revert the change. The better fix would be to also write a test to capture this expectation.

[jaraco]

I can PR that as a starting point.

I went ahead and pulled in the commit. Thanks for putting it together and presenting it in such an accessible way.