Installer: Encapsulate all uses of `._env` and `._path` (#352)

* buildout.cfg: Remove redundancy

Share the eggs definition between the the online and offline tests.

* Remove redundant code

Trying to insert `self._dest` in `self._path`  in `Installer.install()`
is unnecessary since:

 * it's already done in `__init__()`

 * nothing changes either `self._path` or `self._dest` during the
   lifetime of `Installer`

Remove `Installer._load_dist(self, dist)` since it has never been
used in the whole history of Buildout.

Finally, simplify the interface to `._get_dist()` and  `_call_easy_install()`:

All callers to `._get_dist()` add the resulting dist to the WorkingSet. No
reason to do it in `._get_dist()` or to pass the `ws` into
`._call_easy_install()`.

* Be stricter when adding setuptools as requirements

Only do it for namespace package dists that actually need it. I.e. those
that use `pkg_resources.declare_namespace()` instead of
`pkg_util.extend_path()` or PEP 420.

* easy_install: `eggs-directory` may contain more than eggs

Modify the `easy_install.Installer` class to locate not only eggs, but
anything that has a `.dist-info` inside `._dest` (i.e. the Buildout
`eggs-directory`).

This makes it easier for extensions like `buildout.wheel` to add non eggs
inside it: by installing a distribution inside a subdirectory of `._dest` as if
that subdirectory was `site-packages`, you can later locate that
distribution with the Installer.

Conversely, make sure any distribution found in a direct child of `.dest` is
treated as if it was an `egg` distribution (as opposed to a develop
distribution or a site-packages distribution).

All access to `Installer._path` and all access that modifies `._env` is now
done through `Installer` methods, so that Buildout extensions can install
subclasses of `Installer` that alter their behaviour.

* Refactor `_get_dist()` and `_call_easy_install()`

Move the actual invocation of `easy_install` to a module global function
`call_easy_install()`. Simplify its signature so it's simpler to
override in Buildout extensions.

Refactor `._get_dist()` and remove all unpack/install logic into
`_move_to_eggs_dir_and_compile()`, bypassing
`Installer._call_easy_install()`.

`._get_dist()` now calls directly `call_easy_install()` instead. But
only as a fallback to a dictionary lookup of filename extensions to
distribution unpacking methods like:

 - `.egg`: `unpack_egg()`
 - `.whl`: `unpack_wheel()`

This will make it easier for extensions to add support to new dist
formats.

buildout.cfg

@@ -25,9 +25,7 @@ eggs =
 # Tests that can be run wo a network
 [oltest]
 recipe = zc.recipe.testrunner
-eggs =
-  zc.buildout[test]
-  zc.recipe.egg
+eggs = ${test:eggs}
 defaults =
   [
   '-t',

src/zc/buildout/easy_install.py

@@ -169,6 +169,51 @@ def _execute_permission():
 
 _easy_install_cmd = 'from setuptools.command.easy_install import main; main()'
 
+def get_namespace_package_paths(dist):
+    """
+    Generator of the expected pathname of each __init__.py file of the
+    namespaces of a distribution.
+    """
+    base = [dist.location]
+    init = ['__init__.py']
+    for namespace in dist.get_metadata_lines('namespace_packages.txt'):
+        yield os.path.join(*(base + namespace.split('.') + init))
+
+def namespace_packages_need_pkg_resources(dist):
+    if os.path.isfile(dist.location):
+        # Zipped egg, with namespaces, surely needs setuptools
+        return True
+    # If they have `__init__.py` files that use pkg_resources and don't
+    # fallback to using `pkgutil`, then they need setuptools/pkg_resources:
+    for path in get_namespace_package_paths(dist):
+        if os.path.isfile(path):
+            with open(path, 'rb') as f:
+                source = f.read()
+                if (source and
+                        b'pkg_resources' in source and
+                        not b'pkgutil' in source):
+                    return True
+    return False
+
+def dist_needs_pkg_resources(dist):
+    """
+    A distribution needs setuptools/pkg_resources added as requirement if:
+
+        * It has namespace packages declared with:
+        - `pkg_resources.declare_namespace()`
+        * Those namespace packages don't fall back to `pkgutil`
+        * It doesn't have `setuptools/pkg_resources` as requirement already
+    """
+
+    return (
+        dist.has_metadata('namespace_packages.txt') and
+        # This will need to change when `pkg_resources` gets its own
+        # project:
+        'setuptools' not in {r.project_name for r in dist.requires()} and
+        namespace_packages_need_pkg_resources(dist)
+    )
+
+
 class Installer:
 
     _versions = {}
@@ -195,7 +240,7 @@ class Installer:
                  check_picked=True,
                  ):
         assert executable == sys.executable, (executable, sys.executable)
-        self._dest = dest
+        self._dest = dest if dest is None else pkg_resources.normalize_path(dest)
         self._allow_hosts = allow_hosts
 
         if self._install_from_cache:
@@ -213,13 +258,11 @@ class Installer:
 
         self._index_url = index
         path = (path and path[:] or []) + buildout_and_setuptools_path
-        if dest is not None and dest not in path:
-            path.insert(0, dest)
         self._path = path
         if self._dest is None:
             newest = False
         self._newest = newest
-        self._env = pkg_resources.Environment(path)
+        self._env = self._make_env()
         self._index = _get_index(index, links, self._allow_hosts)
         self._requirements_and_constraints = []
         self._check_picked = check_picked
@@ -227,6 +270,39 @@ class Installer:
         if versions is not None:
             self._versions = normalize_versions(versions)
 
+    def _make_env(self):
+        full_path = self._get_dest_dist_paths() + self._path
+        env = pkg_resources.Environment(full_path)
+        # this needs to be called whenever self._env is modified (or we could
+        # make an Environment subclass):
+        self._eggify_env_dest_dists(env, self._dest)
+        return env
+
+    def _env_rescan_dest(self):
+        self._env.scan(self._get_dest_dist_paths())
+        self._eggify_env_dest_dists(self._env, self._dest)
+
+    def _get_dest_dist_paths(self):
+        dest = self._dest
+        if dest is None:
+            return []
+        eggs = glob.glob(os.path.join(dest, '*.egg'))
+        dists = [os.path.dirname(dist_info) for dist_info in
+                 glob.glob(os.path.join(dest, '*', '*.dist-info'))]
+        # sort them like pkg_resources.find_on_path() would
+        return pkg_resources._by_version_descending(set(eggs + dists))
+
+    @staticmethod
+    def _eggify_env_dest_dists(env, dest):
+        """
+        Make sure everything found under `dest` is seen as an egg, even if it's
+        some other kind of dist.
+        """
+        for project_name in env:
+            for dist in env[project_name]:
+                if os.path.dirname(dist.location) == dest:
+                    dist.precedence = pkg_resources.EGG_DIST
+
     def _version_conflict_information(self, name):
         """Return textual requirements/constraint information for debug purposes
 
@@ -330,48 +406,17 @@ class Installer:
             str(req))
         return best_we_have, None
 
-    def _load_dist(self, dist):
-        dists = pkg_resources.Environment(dist.location)[dist.project_name]
-        assert len(dists) == 1
-        return dists[0]
-
-    def _call_easy_install(self, spec, ws, dest, dist):
+    def _call_easy_install(self, spec, dest, dist):
 
         tmp = tempfile.mkdtemp(dir=dest)
         try:
-            path = setuptools_path
-
-            args = [sys.executable, '-c',
-                    ('import sys; sys.path[0:0] = %r; ' % path) +
-                    _easy_install_cmd, '-mZUNxd', tmp]
-            level = logger.getEffectiveLevel()
-            if level > 0:
-                args.append('-q')
-            elif level < 0:
-                args.append('-v')
-
-            args.append(spec)
-
-            if level <= logging.DEBUG:
-                logger.debug('Running easy_install:\n"%s"\npath=%s\n',
-                             '" "'.join(args), path)
-
-            sys.stdout.flush() # We want any pending output first
-
-            exit_code = subprocess.call(list(args))
+            paths = call_easy_install(spec, tmp)
 
             dists = []
-            env = pkg_resources.Environment([tmp])
+            env = pkg_resources.Environment(paths)
             for project in env:
                 dists.extend(env[project])
 
-            if exit_code:
-                logger.error(
-                    "An error occurred when trying to install %s. "
-                    "Look above this message for any errors that "
-                    "were output by easy_install.",
-                    dist)
-
             if not dists:
                 raise zc.buildout.UserError("Couldn't install: %s" % dist)
 
@@ -397,9 +442,7 @@ class Installer:
 
             result = []
             for d in dists:
-                newloc = _move_to_eggs_dir_and_compile(d, dest)
-                [d] = pkg_resources.Environment([newloc])[d.project_name]
-                result.append(d)
+                result.append(_move_to_eggs_dir_and_compile(d, dest))
 
             return result
 
@@ -482,7 +525,7 @@ class Installer:
 
         return dist.clone(location=new_location)
 
-    def _get_dist(self, requirement, ws, for_buildout_run=False):
+    def _get_dist(self, requirement, ws):
         __doing__ = 'Getting distribution for %r.', str(requirement)
 
         # Maybe an existing dist is already the best dist that satisfies the
@@ -518,37 +561,13 @@ class Installer:
                     raise zc.buildout.UserError(
                         "Couldn't download distribution %s." % avail)
 
-                if dist.location.endswith('.whl'):
-                    dist = wheel_to_egg(dist, tmp)
-
-                if dist.precedence == pkg_resources.EGG_DIST:
-                    # It's already an egg, just fetch it into the dest
-                    newloc = _move_to_eggs_dir_and_compile(dist, self._dest)
-
-                    # Getting the dist from the environment causes the
-                    # distribution meta data to be read.  Cloning isn't
-                    # good enough.
-                    dists = pkg_resources.Environment([newloc])[
-                        dist.project_name]
-                else:
-                    # It's some other kind of dist.  We'll let easy_install
-                    # deal with it:
-                    dists = self._call_easy_install(
-                        dist.location, ws, self._dest, dist)
-                    for dist in dists:
-                        if for_buildout_run:
-                            # ws is the global working set and we're
-                            # installing buildout, setuptools, extensions or
-                            # recipes. Make sure that whatever correct version
-                            # we've just installed is the active version,
-                            # hence the ``replace=True``.
-                            ws.add(dist, replace=True)
+                dists = [_move_to_eggs_dir_and_compile(dist, self._dest)]
 
             finally:
                 if tmp != self._download_cache:
                     shutil.rmtree(tmp)
 
-            self._env.scan([self._dest])
+            self._env_rescan_dest()
             dist = self._env.best_match(requirement, ws)
             logger.info("Got %s.", dist)
 
@@ -556,23 +575,32 @@ class Installer:
             dists = [dist]
 
         if not self._install_from_cache and self._use_dependency_links:
+            self._add_dependency_links_from_dists(dists)
+
+        if self._check_picked:
+            self._check_picked_requirement_versions(requirement, dists)
+
+        return dists
+
+    def _add_dependency_links_from_dists(self, dists):
+        reindex = False
+        links = self._links
         for dist in dists:
             if dist.has_metadata('dependency_links.txt'):
                 for link in dist.get_metadata_lines('dependency_links.txt'):
                     link = link.strip()
-                        if link not in self._links:
+                    if link not in links:
                         logger.debug('Adding find link %r from %s',
                                      link, dist)
-                            self._links.append(link)
-                            self._index = _get_index(self._index_url,
-                                                     self._links,
-                                                     self._allow_hosts)
+                        links.append(link)
+                        reindex = True
+        if reindex:
+            self._index = _get_index(self._index_url, links, self._allow_hosts)
 
-        if self._check_picked:
-            # Check whether we picked a version and, if we did, report it:
+    def _check_picked_requirement_versions(self, requirement, dists):
+        """ Check whether we picked a version and, if we did, report it """
         for dist in dists:
-                if not (
-                    dist.precedence == pkg_resources.DEVELOP_DIST
+            if not (dist.precedence == pkg_resources.DEVELOP_DIST
                 or
                 (len(requirement.specs) == 1
                  and
@@ -588,14 +616,8 @@ class Installer:
                                              dist.version)
                         )
 
-        return dists
-
     def _maybe_add_setuptools(self, ws, dist):
-        if dist.has_metadata('namespace_packages.txt'):
-            for r in dist.requires():
-                if r.project_name in ('setuptools', 'setuptools'):
-                    break
-            else:
+        if dist_needs_pkg_resources(dist):
             # We have a namespace package but no requirement for setuptools
             if dist.precedence == pkg_resources.DEVELOP_DIST:
                 logger.warn(
@@ -610,7 +632,6 @@ class Installer:
                 for dist in self._get_dist(requirement, ws):
                     ws.add(dist)
 
-
     def _constrain(self, requirement):
         """Return requirement with optional [versions] constraint added."""
         constraint = self._versions.get(requirement.project_name.lower())
@@ -632,10 +653,6 @@ class Installer:
             "Base installation request: %s" % repr(specs)[1:-1])
 
         for_buildout_run = bool(working_set)
-        path = self._path
-        dest = self._dest
-        if dest is not None and dest not in path:
-            path.insert(0, dest)
 
         requirements = [self._constrain(pkg_resources.Requirement.parse(spec))
                         for spec in specs]
@@ -646,8 +663,7 @@ class Installer:
             ws = working_set
 
         for requirement in requirements:
-            for dist in self._get_dist(requirement, ws,
-                                       for_buildout_run=for_buildout_run):
+            for dist in self._get_dist(requirement, ws):
                 ws.add(dist)
                 self._maybe_add_setuptools(ws, dist)
 
@@ -691,13 +707,12 @@ class Installer:
                     if not for_buildout_run:
                         raise VersionConflict(err, ws)
             if dist is None:
-                if dest:
+                if self._dest:
                     logger.debug('Getting required %r', str(req))
                 else:
                     logger.debug('Adding required %r', str(req))
                 self._log_requirement(ws, req)
-                for dist in self._get_dist(req, ws,
-                                           for_buildout_run=for_buildout_run):
+                for dist in self._get_dist(req, ws):
                     ws.add(dist)
                     self._maybe_add_setuptools(ws, dist)
             if dist not in req:
@@ -775,9 +790,7 @@ class Installer:
                 setuptools.command.setopt.edit_config(
                     setup_cfg, dict(build_ext=build_ext))
 
-                dists = self._call_easy_install(
-                    base, pkg_resources.WorkingSet(),
-                    self._dest, dist)
+                dists = self._call_easy_install(base, self._dest, dist)
 
                 return [dist.location for dist in dists]
             finally:
@@ -1564,6 +1577,84 @@ class IncompatibleConstraintError(zc.buildout.UserError):
 IncompatibleVersionError = IncompatibleConstraintError # Backward compatibility
 
 
+def call_easy_install(spec, dest):
+    """
+    Call `easy_install` from setuptools as a subprocess to install a
+    distribution specified by `spec` into `dest`.
+    Returns all the paths inside `dest` created by the above.
+    """
+    path = setuptools_path
+
+    args = [sys.executable, '-c',
+            ('import sys; sys.path[0:0] = %r; ' % path) +
+            _easy_install_cmd, '-mZUNxd', dest]
+    level = logger.getEffectiveLevel()
+    if level > 0:
+        args.append('-q')
+    elif level < 0:
+        args.append('-v')
+
+    args.append(spec)
+
+    if level <= logging.DEBUG:
+        logger.debug('Running easy_install:\n"%s"\npath=%s\n',
+                        '" "'.join(args), path)
+
+    sys.stdout.flush() # We want any pending output first
+
+    exit_code = subprocess.call(list(args))
+
+    if exit_code:
+        logger.error(
+            "An error occurred when trying to install %s. "
+            "Look above this message for any errors that "
+            "were output by easy_install.",
+            spec)
+    return glob.glob(os.path.join(dest, '*'))
+
+
+def unpack_egg(location, dest):
+    # Buildout 2 no longer installs zipped eggs,
+    # so we always want to unpack it.
+    dest = os.path.join(dest, os.path.basename(location))
+    setuptools.archive_util.unpack_archive(location, dest)
+
+
+WHEEL_TO_EGG_WARNING = """
+Using unpack_wheel() shim over deprecated wheel_to_egg().
+Please update your wheel extension implementation for one that installs a .whl
+handler in %s.UNPACKERS
+""".strip() % (__name__,)
+
+def unpack_wheel(location, dest):
+    logger.warning(WHEEL_TO_EGG_WARNING)
+    # Deprecated backward compatibility shim. Please do not use.
+    basename = os.path.basename(location)
+    dists = setuptools.package_index.distros_for_location(location, basename)
+    wheel_to_egg(list(dists)[0], dest)
+    
+
+UNPACKERS = {
+    # Buildout 2 no longer installs zipped eggs, so we always want to unpack it.
+    '.egg': unpack_egg,
+    '.whl': unpack_wheel,
+}
+
+
+def _get_matching_dist_in_location(dist, location):
+    """
+    Check if `locations` contain only the one intended dist.
+    Return the dist with metadata in the new location.
+    """
+    # Getting the dist from the environment causes the
+    # distribution meta data to be read.  Cloning isn't
+    # good enough.
+    env = pkg_resources.Environment([location])
+    dists = [ d for project_name in env for d in env[project_name] ]
+    dist_infos = [ (d.project_name, d.version) for d in dists ]
+    if dist_infos == [(dist.project_name, dist.version)]:
+        return dists.pop()
+
 def _move_to_eggs_dir_and_compile(dist, dest):
     """Move distribution to the eggs destination directory.
 
@@ -1575,7 +1666,7 @@ def _move_to_eggs_dir_and_compile(dist, dest):
     running in parallel.  So we copy to a temporary directory first.
     See discussion at https://github.com/buildout/buildout/issues/307
 
-    We return the new location.
+    We return the new distribution with properly loaded metadata.
     """
     # First make sure the destination directory exists.  This could suffer from
     # the same kind of race condition as the rest: if we check that it does not
@@ -1587,23 +1678,26 @@ def _move_to_eggs_dir_and_compile(dist, dest):
         if not os.path.isdir(dest):
             # Unknown reason.  Reraise original error.
             raise
-    newloc = os.path.join(
-        dest, os.path.basename(dist.location))
     tmp_dest = tempfile.mkdtemp(dir=dest)
     try:
-        tmp_egg_dir = os.path.join(tmp_dest, os.path.basename(dist.location))
-        if os.path.isdir(dist.location):
-            # We got a directory. It must have been obtained locally.
+        if (os.path.isdir(dist.location) and
+                dist.precedence >= pkg_resources.BINARY_DIST):
+            # We got a pre-built directory. It must have been obtained locally.
             # Just copy it.
-            shutil.copytree(dist.location, tmp_egg_dir)
+            tmp_loc = os.path.join(tmp_dest, os.path.basename(dist.location))
+            shutil.copytree(dist.location, tmp_loc)
         else:
-            # It is a zipped egg.  Buildout 2 no longer installs zipped eggs,
-            # so we always want to unpack it.
-            setuptools.archive_util.unpack_archive(
-                dist.location, tmp_egg_dir)
-        # We have copied the egg. Now try to rename/move it.
+            # It is an archive of some sort.
+            # Figure out how to unpack it, or fall back to easy_install.
+            _, ext = os.path.splitext(dist.location)
+            unpacker = UNPACKERS.get(ext, call_easy_install)
+            unpacker(dist.location, tmp_dest)
+            [tmp_loc] = glob.glob(os.path.join(tmp_dest, '*'))
+
+        # We have installed the dist. Now try to rename/move it.
+        newloc = os.path.join(dest, os.path.basename(tmp_loc))
         try:
-            os.rename(tmp_egg_dir, newloc)
+            os.rename(tmp_loc, newloc)
         except OSError:
             # Might be for various reasons.  If it is because newloc already
             # exists, we can investigate.
@@ -1611,7 +1705,8 @@ def _move_to_eggs_dir_and_compile(dist, dest):
                 # No, it is a different reason.  Give up.
                 raise
             # Try to use it as environment and check if our project is in it.
-            if not pkg_resources.Environment([newloc])[dist.project_name]:
+            newdist = _get_matching_dist_in_location(dist, newloc)
+            if newdist is None:
                 # Path exists, but is not our package.  We could
                 # try something, but it seems safer to bail out
                 # with the original error.
@@ -1627,7 +1722,9 @@ def _move_to_eggs_dir_and_compile(dist, dest):
             # There were no problems during the rename.
             # Do the compile step.
             redo_pyc(newloc)
+            newdist = _get_matching_dist_in_location(dist, newloc)
+            assert newdist is not None  # newloc above is missing our dist?!
     finally:
         # Remember that temporary directories must be removed
         shutil.rmtree(tmp_dest)
-    return newloc
+    return newdist

src/zc/buildout/tests.py

@@ -836,12 +836,15 @@ and we will get setuptools included in the working set.
     ...        'zc.buildout.easy_install', level=logging.WARNING)
     >>> logging.getLogger('zc.buildout.easy_install').propagate = False
 
-    >>> [dist.project_name
+    >>> def get_working_set(*project_names):
+    ...     paths = [join(sample_buildout, 'eggs'),
+    ...              join(sample_buildout, 'develop-eggs')]
+    ...     return [
+    ...        dist.project_name
     ...        for dist in zc.buildout.easy_install.working_set(
-    ...    ['foox'], sys.executable,
-    ...    [join(sample_buildout, 'eggs'),
-    ...     join(sample_buildout, 'develop-eggs'),
-    ...     ])]
+    ...            project_names, sys.executable, paths)
+    ...     ]
+    >>> get_working_set('foox')
     ['foox', 'setuptools']
 
     >>> print_(handler)
@@ -851,13 +854,15 @@ and we will get setuptools included in the working set.
 
     >>> handler.clear()
 
-On the other hand, if we have a regular egg, rather than a develop egg:
+On the other hand, if we have a zipped egg, rather than a develop egg:
 
     >>> os.remove(join('develop-eggs', 'foox.egg-link'))
 
-    >>> _ = system(join('bin', 'buildout') + ' setup foo bdist_egg -d'
-    ...            + join(sample_buildout, 'eggs'))
-
+    >>> _ = system(join('bin', 'buildout') + ' setup foo bdist_egg')
+    >>> foox_dist = join('foo', 'dist')
+    >>> import glob
+    >>> [foox_egg] = glob.glob(join(foox_dist, 'foox-*.egg'))
+    >>> _ = shutil.copy(foox_egg, join(sample_buildout, 'eggs'))
     >>> ls('develop-eggs')
     -  zc.recipe.egg.egg-link
 
@@ -870,17 +875,27 @@ On the other hand, if we have a regular egg, rather than a develop egg:
 
 We do not get a warning, but we do get setuptools included in the working set:
 
-    >>> [dist.project_name
-    ...  for dist in zc.buildout.easy_install.working_set(
-    ...    ['foox'], sys.executable,
-    ...    [join(sample_buildout, 'eggs'),
-    ...     join(sample_buildout, 'develop-eggs'),
-    ...     ])]
+    >>> get_working_set('foox')
+    ['foox', 'setuptools']
+
+    >>> print_(handler, end='')
+
+Likewise for an unzipped egg:
+
+    >>> foox_egg_basename = os.path.basename(foox_egg)
+    >>> os.remove(join(sample_buildout, 'eggs', foox_egg_basename))
+    >>> _ = zc.buildout.easy_install.install(
+    ...     ['foox'], join(sample_buildout, 'eggs'), links=[foox_dist],
+    ...     index='file://' + foox_dist)
+    >>> ls('develop-eggs')
+    -  zc.recipe.egg.egg-link
+
+    >>> get_working_set('foox')
     ['foox', 'setuptools']
 
     >>> print_(handler, end='')
 
-We get the same behavior if the it is a dependency that uses a
+We get the same behavior if it is a dependency that uses a
 namespace package.
 
 
@@ -903,12 +918,7 @@ namespace package.
     Develop: '/sample-buildout/foo'
     Develop: '/sample-buildout/bar'
 
-    >>> [dist.project_name
-    ...  for dist in zc.buildout.easy_install.working_set(
-    ...    ['bar'], sys.executable,
-    ...    [join(sample_buildout, 'eggs'),
-    ...     join(sample_buildout, 'develop-eggs'),
-    ...     ])]
+    >>> get_working_set('bar')
     ['bar', 'foox', 'setuptools']
 
     >>> print_(handler, end='')
@@ -916,6 +926,32 @@ namespace package.
       Develop distribution: foox 0.0.0
     uses namespace packages but the distribution does not require setuptools.
 
+On the other hand, if the distribution uses ``pkgutil.extend_path()`` to
+implement its namespaces, even if just as fallback from the absence of
+``pkg_resources``, then ``setuptools`` shoudn't be added as requirement to
+its unzipped egg:
+
+    >>> foox_installed_egg = join(sample_buildout, 'eggs', foox_egg_basename)
+    >>> namespace_init = join(foox_installed_egg, 'stuff', '__init__.py')
+    >>> write(namespace_init,
+    ... """try:
+    ...     __import__('pkg_resources').declare_namespace(__name__)
+    ... except ImportError:
+    ...     __path__ = __import__('pkgutil').extend_path(__path__, __name__)
+    ... """)
+
+    >>> os.remove(join('develop-eggs', 'foox.egg-link'))
+    >>> os.remove(join('develop-eggs', 'bar.egg-link'))
+    >>> get_working_set('foox')
+    ['foox']
+
+The same goes for packages using PEP420 namespaces
+
+    >>> os.remove(namespace_init)
+    >>> get_working_set('foox')
+    ['foox']
+
+Cleanup:
 
     >>> logging.getLogger('zc.buildout.easy_install').propagate = True
     >>> handler.uninstall()
@@ -3155,8 +3191,7 @@ class UnitTests(unittest.TestCase):
         def wheel_to_egg(dist, dest):
             newloc = os.path.join(dest, egg_name)
             shutil.copy(dist.location, newloc)
-            return pkg_resources.Distribution.from_location(newloc,
-                                                            'demo-0.3.whl')
+            return pkg_resources.Distribution.from_filename(newloc)
         zc.buildout.easy_install.wheel_to_egg = wheel_to_egg
         egg_dir = os.path.join(self.sample_buildout, 'eggs')
         self.assertFalse(egg_name in os.listdir(egg_dir))