[wkrd] Warn when bootstrap finds .{dist|egg}-info

And avoid creating a .egg-link pointing to their location.

src/zc/buildout/buildout.py

@@ -764,13 +764,7 @@ class Buildout(DictMixin):
 
         # XXX Note: except if the current modules are not eggs. In particular,
         # this concerns .dist-info packages installed by pip in site-packages
-        # or elsewhere: setuptools does not distinguish dists installed by pip
-        # from actual develop dists. This may lead to the creation of .egg-link
-        # files in ./develop-eggs linking to the original location.
-        # A special-case exception is made when the location is site-packages
-        # to avoid putting links to site-packages in ./develop-eggs. This is
-        # merely a mitigation and does not preclude other shared locations
-        # being linked in ./develop-eggs.
+        # or elsewhere.
 
         # Sort the working set to keep entries with single dists first.
         options = self['buildout']
@@ -787,6 +781,9 @@ class Buildout(DictMixin):
         # Now copy buildout and setuptools eggs, and record destination eggs.
         # XXX Note: dists using .dist-info format - e.g. packages installed by
         # pip in site-packages - will be seen as develop dists and not copied.
+        # Instead of linking them in ./develop-eggs like actual develop dists,
+        # a warning is emitted to avoid linking a directory that can contain
+        # multiple dists, with unintended and unexpected results later.
         egg_entries = []
         develop_dists = []
         for dist in ws:
@@ -800,12 +797,19 @@ class Buildout(DictMixin):
                         "Consider using 'buildout:extra-paths=' to install it "
                         "from scratch in isolation directly in eggs-directory."
                         % (dist, dist.location))
-                    # XXX: TODO: Ideally we should be able to distinguish
-                    # .dist-info dists from develop dists, and support bundling
-                    # .dist-info packages into individual '.dist' bundles that
-                    # could be put in ./eggs, with support in buildout for
-                    # using such distribution.
                     continue
+                elif zc.buildout.easy_install.is_externally_managed_dist(dist):
+                    # Exception for .dist-info and .egg-info
+                    self._logger.warning(
+                        "Distribution %s (%s) is a .dist-info or a .egg-info. "
+                        "Avoiding creating a link in develop-eggs-directory.\n"
+                        "Consider using 'buildout:extra-paths=' to install it "
+                        "from scratch in isolation directly in eggs-directory."
+                        % (dist, dist.location))
+                    continue
+                # XXX: Maybe support bundling <project>.dist-info and <project>
+                # into a containing <project>.dist directory and copying it in
+                # ./eggs when the dist found is a .dist-info.
                 dest = os.path.join(self['buildout']['develop-eggs-directory'],
                                     dist.key + '.egg-link')
                 with open(dest, 'w') as fh:

src/zc/buildout/easy_install.py

@@ -1910,6 +1910,16 @@ UNPACKERS = {
 }
 
 
+def is_dist_info(dist):
+    return isinstance(dist, pkg_resources.DistInfoDistribution)
+
+def is_egg_info(dist):
+    return isinstance(dist, pkg_resources.EggInfoDistribution)
+
+def is_externally_managed_dist(dist):
+    return is_dist_info(dist) or is_egg_info(dist)
+
+
 def _get_matching_dist_in_location(dist, location):
     """
     Check if `locations` contain only the one intended dist.