Adds a link verb to buildout allowing to just link to local buildout directories

if the current buildout is already compiled

src/zc/buildout/buildout.py

@@ -1799,6 +1799,17 @@ def _open(base, filename, seen, dl_options, override, downloaded):
         os.remove(downloaded_filename)
 
     options = result.get('buildout', {})
+    link = options.pop('link', "")
+    shared_path = shared_stack_path(link)
+    if link and shared_path:
+        shared_item_set = set(os.listdir(shared_path))
+        current_item_set = set(os.listdir('.'))
+        for item in shared_item_set - current_item_set:
+            os.symlink(os.path.join(shared_path, item), item)
+        Buildout.install = lambda *args : None
+    elif link:
+      options['extends'] = link
+
     extends = options.pop('extends', None)
     if 'extended-by' in options:
         raise zc.buildout.UserError(
@@ -1833,6 +1844,12 @@ def _open(base, filename, seen, dl_options, override, downloaded):
     seen.pop()
     return result
 
+def shared_stack_path(link):
+  # md5digest copied from slapos.core. Better to copy/paste more than adding
+  # dependencies to buildout
+  link_md5 = md5(link).hexdigest()
+  shared_stack_path = os.path.join('/', 'opt', 'slapgrid', link_md5)
+  return (shared_stack_path if os.path.exists(shared_stack_path) else None)
 
 ignore_directories = '.svn', 'CVS', '__pycache__'
 _dir_hashes = {}