egg_info: Split manifest_maker._add_egg_info into its own method

On Sat, Oct 11, 2014 at 04:23:37PM -0000, Jason R. Coombs wrote [1]:
> I suggest implementing the functionality as a separate method with a
> docstring explaining the purpose.

so that's what we have here. The docstring is adapted from the
cbd4f603 (egg_info: Search egg-base for files to add to the manifest,
2014-10-16) commit message.

It's a lot of docs for a single command (although there is a newsted
list comprehension), so I'm fine if you drop this commit before
merging. The motivation behind the lines would still be available in
the version control history:

  $ hg blame -c setuptools/command/egg_info.py | grep -A1 ei_cmd.egg_base
  cbd4f6038604: if ei_cmd.egg_base != os.curdir:
  cbd4f6038604: self.filelist.allfiles.extend([
  cbd4f6038604: os.path.join(ei_cmd.egg_base, path)
  cbd4f6038604: for path in distutils.filelist.findall(ei_cmd.egg_base)])
  80108b046cb6: self.filelist.include_pattern("*", prefix=ei_cmd.egg_info)
  $ hg log -vr cbd4f6038604
  changeset: 3163:cbd4f6038604
  ...
  description:
  egg_info: Search egg-base for files to add to the manifest
  Before this commit, this:

    $ mkdir -p /tmp/xyz/{home,lib,scripts,data,egg}
    $ cat >/tmp/xyz/home/.pydistutils.cfg <<EOF
  ...

[1]: https://bitbucket.org/pypa/setuptools/pull-request/85/egg_info-search-egg-base-for-files-to-add/diff#comment-3418032

setuptools/command/egg_info.py

@@ -326,11 +326,28 @@ class manifest_maker(sdist):
             self.read_manifest()
         ei_cmd = self.get_finalized_command('egg_info')
         if ei_cmd.egg_base != os.curdir:
-            self.filelist.allfiles.extend([
-                os.path.join(ei_cmd.egg_base, path)
-                for path in distutils.filelist.findall(ei_cmd.egg_base)])
+            self._add_egg_info(cmd=ei_cmd)
         self.filelist.include_pattern("*", prefix=ei_cmd.egg_info)
 
+    def _add_egg_info(self, cmd):
+        """Add paths for egg-info files for an external egg-base.
+
+        The egg-info files are written to egg-base.  If egg-base is
+        outside the current working directory, we need a separate step
+        (this method) to search the egg-base directory when creating
+        the manifest.  We use distutils.filelist.findall (which is
+        really the version monkeypatched in by setuptools/__init__.py)
+        to perform the search.
+
+        Since findall records relative paths, prefix the returned
+        paths with cmd.egg_base, so add_default's include_pattern call
+        (which is looking for the absolute cmd.egg_info) will match
+        them.
+        """
+        self.filelist.allfiles.extend([
+            os.path.join(cmd.egg_base, path)
+            for path in distutils.filelist.findall(cmd.egg_base)])
+
     def prune_file_list(self):
         build = self.get_finalized_command('build')
         base_dir = self.distribution.get_fullname()