egg_info: Touch 'egg-info' directory

'tox' determines whether a package should be rebuilt by comparing the
timestamp of the package's 'egg-info' directory and its 'setup.py' or
'setup.cfg' files [1][2]. Unfortunately this checks the 'egg-info'
directory itself, which is not updated, unlike the contents of that
directory. This means that 'tox' will always rebuild the package once
one of the two setup files has been updated.

While this is clearly a bug in 'tox' that should be fixed separately,
there is merit in using this as a heuristic so enable it.

[1] https://github.com/tox-dev/tox/blob/3.1.0/src/tox/venv.py#L253-L257
[2] https://github.com/tox-dev/tox/blob/3.1.0/src/tox/venv.py#L221-L244Signed-off-by: Stephen Finucane <stephen@that.guru>

changelog.d/1427.change.rst

+Set timestamp of ``.egg-info`` directory whenever ``egg_info`` command is run.

setuptools/command/egg_info.py

@@ -281,6 +281,7 @@ class egg_info(InfoCommon, Command):
 
     def run(self):
         self.mkpath(self.egg_info)
+        os.utime(self.egg_info, None)
         installer = self.distribution.fetch_build_egg
         for ep in iter_entry_points('egg_info.writers'):
             ep.require(installer=installer)

setuptools/tests/test_egg_info.py

+import datetime
 import sys
 import ast
 import os
 import glob
 import re
 import stat
+import time
 
 from setuptools.command.egg_info import egg_info, manifest_maker
 from setuptools.dist import Distribution
@@ -146,6 +148,21 @@ class TestEggInfo:
         ]
         assert sorted(actual) == expected
 
+    def test_rebuilt(self, tmpdir_cwd, env):
+        """Ensure timestamps are updated when the command is re-run."""
+        self._create_project()
+
+        self._run_egg_info_command(tmpdir_cwd, env)
+        timestamp_a = os.path.getmtime('foo.egg-info')
+
+        # arbitrary sleep just to handle *really* fast systems
+        time.sleep(.001)
+
+        self._run_egg_info_command(tmpdir_cwd, env)
+        timestamp_b = os.path.getmtime('foo.egg-info')
+
+        assert timestamp_a != timestamp_b
+
     def test_manifest_template_is_read(self, tmpdir_cwd, env):
         self._create_project()
         build_files({