Extract methods to separate _safe_data_files behavior and _add_data_files. Simplify warning.

Author: jaraco

setuptools/command/sdist.py

@@ -126,23 +126,31 @@ def _add_defaults_python(self):
         if self.distribution.has_pure_modules():
             build_py = self.get_finalized_command('build_py')
             self.filelist.extend(build_py.get_source_files())
+            self._add_data_files(self._safe_data_files(build_py))
 
-            # This functionality is incompatible with include_package_data, and
-            # will in fact create an infinite recursion if include_package_data
-            # is True.  Use of include_package_data will imply that
-            # distutils-style automatic handling of package_data is disabled
-
-            if self.distribution.include_package_data:
-                self.warn(
-                    "Either specify package_data manually, or use "
-                    "include_package_data=True, but not both. Proceeding as if "
-                    "package_data was not specified."
-                )
+    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.
+        """
+        if self.distribution.include_package_data:
+            self.warn(
+                "Distutils 'package_data' ignored due to "
+                "'include_package_data'."
+            )
+            return ()
+        return build_py.data_files
 
-            else:
-                for _, src_dir, _, filenames in build_py.data_files:
-                    self.filelist.extend([os.path.join(src_dir, filename)
-                                          for filename in filenames])
+    def _add_data_files(self, data_files):
+        """
+        Add data files as found in build_py.data_files.
+        """
+        self.filelist.extend(
+            os.path.join(src_dir, name)
+            for _, src_dir, _, filenames in data_files
+            for name in filenames
+        )
 
     def _add_defaults_data_files(self):
         try:

setuptools/tests/test_manifest.py

@@ -624,8 +624,5 @@ def test_warning_on_meaningless_parameter_combination(self):
         mm.warn = mock.Mock()
         mm.run()
 
-        mm.warn.assert_called_with(
-            "Either specify package_data manually, or use "
-            "include_package_data=True, but not both. Proceeding as if "
-            "package_data was not specified."
-        )
+        msg = "Distutils 'package_data' ignored due to 'include_package_data'."
+        mm.warn.assert_called_with(msg)