[fix] Sign develop eggs with directory hash

Mark .dist-info eggs installed by buildout as develop to distinguish
them from .dist-info eggs from the system and decide how to sign the
egg accordingly (with directory hash or with version).

src/zc/buildout/buildout.py

@@ -2322,6 +2322,25 @@ def _dir_hash(dir):
     _dir_hashes[dir] = dir_hash = hash.hexdigest()
     return dir_hash
 
+def _is_develop(dist):
+    # Best effort guess on whether a dist was installed as develop dist
+    if dist.precedence != pkg_resources.DEVELOP_DIST:
+        return False
+    elif dist.location == zc.buildout.easy_install.python_lib:
+        return False
+    elif isinstance(dist, pkg_resources.EggInfoDistribution):
+        return True
+    elif isinstance(dist, pkg_resources.DistInfoDistribution):
+        dist_info = dist.egg_info
+        try:
+            with open(os.path.join(dist_info, 'INSTALLER')) as f:
+                return zc.buildout.easy_install.DEVELOP_INSTALLER in f.read()
+        except IOError as e:
+            if e.errno != errno.ENOENT:
+                raise
+        return False
+    return True
+
 def _dists_sig(dists):
     seen = set()
     result = []
@@ -2329,11 +2348,8 @@ def _dists_sig(dists):
         if dist in seen:
             continue
         seen.add(dist)
-        location = dist.location
-        if (dist.precedence == pkg_resources.DEVELOP_DIST
-            and location != zc.buildout.easy_install.python_lib
-            and not isinstance(dist, pkg_resources.DistInfoDistribution)):
-            result.append(dist.project_name + '-' + _dir_hash(location))
+        if _is_develop(dist):
+            result.append(dist.project_name + '-' + _dir_hash(dist.location))
         else:
             result.append(dist.project_name + '-' + dist.version)
     return result

src/zc/buildout/easy_install.py

@@ -1178,6 +1178,7 @@ def _detect_distutils_scripts(egg_name, directory):
         _develop_distutils_scripts[egg_name] = scripts_found
 
 
+DEVELOP_INSTALLER = 'buildout:develop'
 def develop(setup, dest, build_ext=None, executable=None, verbosity=-10):
     if executable is not None: # BBB
         assert executable == sys.executable, (executable, sys.executable)
@@ -1313,6 +1314,10 @@ def develop(setup, dest, build_ext=None, executable=None, verbosity=-10):
                     "Falling back to project's root directory"
                     % (directory, packages),)
                 import_path = directory
+            # Mark this dist as installed by buildout as develop
+            if entry.endswith('.dist-info'):
+                with open(os.path.join(entry_path, 'INSTALLER'), 'w') as f:
+                    f.write(DEVELOP_INSTALLER)
             # Move the .dist-info folder to the import path like setuptools.
             move(entry_path, os.path.join(import_path, project_name + ext))
             # Create a temporary .egg-link.