Fix 1461: Better loop breaker for manifest_maker

The inconsistency for the `package_data` configuration in sdists
when `include_package_data=True` in #1461 have been causing some
problems for the community for a while, as also shown in #2835.

As pointed out by
[@jaraco](#1461 (comment)),
this was being caused by a mechanism to break the recursion between the
`egg_info` and `sdist` commands.

In summary the loop is caused by the following behaviour:

- the `egg_info` command uses a subclass of `sdist` (`manifest_maker`)
  to calculate the MANIFEST,
- the `sdist` class needs to know the MANIFEST to calculate the data files when
  `include_package_data=True`

Previously, the mechanism to break this loop was to simply ignore
the data files in `sdist` when `include_package_data=True`.

The approach implemented in this change was to replace this mechanism,
by allowing `manifest_maker` to override the `_safe_data_files` method
from `sdist`.

---

Please notice [an extensive experiment]
(https://github.com/abravalheri/experiment-setuptools-package-data)
was carried out to investigate the previous confusing behaviour.

There is also [a simplified theoretical analysis]
(pyscaffold/pyscaffold#535 (comment))
comparing the observed behavior in the experiment and the expected
one. This analysis point out to the same offender indicated by
[@jaraco](#1461 (comment))
(which is being replaced in this change).

changelog.d/1461.change.rst

@@ -0,0 +1,3 @@
+Fix inconsistency with ``include_package_data`` and ``packages_data`` in sdist
+by replacing the loop breaking mechanism between the ``sdist`` and
+``egg_info`` commands -- by :user:`abravalheri`

setuptools/command/build_py.py

@@ -67,6 +67,19 @@ def _get_data_files(self):
         self.analyze_manifest()
         return list(map(self._get_pkg_data_files, self.packages or ()))
 
+    def get_data_files_without_manifest(self):
+        """
+        Generate list of ``(package,src_dir,build_dir,filenames)`` tuples,
+        but without triggering any attempt to analyze or build the manifest.
+        """
+        # Avoid triggering dynamic behavior in __getattr__
+        if 'data_files' in self.__dict__:
+            return self.data_files
+        # Prevent eventual errors from unset `manifest_files`
+        # (that would otherwise be set by `analyze_manifest`)
+        self.__dict__.setdefault('manifest_files', {})
+        return list(map(self._get_pkg_data_files, self.packages or ()))
+
     def _get_pkg_data_files(self, package):
         # Locate package source directory
         src_dir = self.get_package_dir(package)

setuptools/command/egg_info.py

@@ -608,6 +608,17 @@ def prune_file_list(self):
         self.filelist.exclude_pattern(r'(^|' + sep + r')(RCS|CVS|\.svn)' + sep,
                                       is_regex=1)
 
+    def _safe_data_files(self, build_py):
+        """
+        The parent class implementation of this method (``sdist``) will try to
+        include data files, which might cause recursion problems, when
+        ``include_package_data=True``.
+
+        Therefore we have to avoid triggering any attempt of analyzing/building
+        the manifest again.
+        """
+        return build_py.get_data_files_without_manifest()
+
 
 def write_file(filename, contents):
     """Create a file with the specified name and write 'contents' (a

setuptools/command/sdist.py

@@ -114,12 +114,15 @@ def _add_defaults_python(self):
 
     def _safe_data_files(self, build_py):
         """
-        Extracting data_files from build_py is known to cause
-        infinite recursion errors when `include_package_data`
-        is enabled, so suppress it in that case.
+        Since the ``sdist`` class is also used to compute the MANIFEST
+        (via :obj:`setuptools.command.egg_info.manifest_maker`),
+        there might be recursion problems when trying to obtain the list of
+        data_files and ``include_package_data=True`` (which in turn depends on
+        the files included in the MANIFEST).
+
+        To avoid that, ``manifest_maker`` should be able to overwrite this
+        method and avoid recursive attempts to build/analyze the MANIFEST.
         """
-        if self.distribution.include_package_data:
-            return ()
         return build_py.data_files
 
     def _add_data_files(self, data_files):

setuptools/tests/test_sdist.py

@@ -126,6 +126,30 @@ def test_package_data_in_sdist(self):
         assert os.path.join('sdist_test', 'c.rst') not in manifest
         assert os.path.join('d', 'e.dat') in manifest
 
+    def test_package_data_and_include_package_data_in_sdist(self):
+        """Make sure there is no recursion when ``include_package_data=True``.
+
+        The mention to a recursion can be first found in:
+        https://github.com/pypa/setuptools/commit/f6cb3d29d919ff6b9313b8a3281c66cfb368c29b
+        """
+
+        setup_attrs = {**SETUP_ATTRS, 'include_package_data': True}
+        assert setup_attrs['package_data']  # make sure we have both options
+
+        dist = Distribution(setup_attrs)
+        dist.script_name = 'setup.py'
+        cmd = sdist(dist)
+        cmd.ensure_finalized()
+
+        with quiet():
+            cmd.run()
+
+        manifest = cmd.filelist.files
+        assert os.path.join('sdist_test', 'a.txt') in manifest
+        assert os.path.join('sdist_test', 'b.txt') in manifest
+        assert os.path.join('sdist_test', 'c.rst') not in manifest
+        assert os.path.join('d', 'e.dat') in manifest
+
     def test_setup_py_exists(self):
         dist = Distribution(SETUP_ATTRS)
         dist.script_name = 'foo.py'