Add '--skip-signature-check' option.

src/zc/buildout/buildout.py

@@ -220,6 +220,7 @@ _buildout_default_options = _annotate_section({
     'newest': 'true',
     'offline': 'false',
     'dry-run': 'false',
+    'check-signature': 'true',
     'parts-directory': 'parts',
     'prefer-final': 'false',
     'python': 'buildout',
@@ -330,6 +331,7 @@ class Buildout(UserDict.DictMixin):
         self.offline = (buildout_section['offline'] == 'true')
         self.newest = (buildout_section['newest'] == 'true')
         self.dry_run = (buildout_section['dry-run'] == 'true')
+        self.check_signature = (buildout_section['check-signature'] == 'true')
         self.accept_buildout_test_releases = (
             buildout_section['accept-buildout-test-releases'] == 'true')
 
@@ -720,6 +722,19 @@ class Buildout(UserDict.DictMixin):
                     old_options = installed_part_options[part].copy()
                     installed_files = old_options.pop('__buildout_installed__')
                     new_options = self.get(part)
+                    if not self.check_signature:
+                        old_signature = old_options.get(
+                            '__buildout_signature__', None)
+                        new_signature = new_options.get(
+                            '__buildout_signature__', None)
+                        if old_signature != new_signature:
+                            self._logger.info(
+                                '[%s]: __buildout_signature__ is different '
+                                'but ignored.' % part)
+                            if old_signature:
+                                new_options['__buildout_signature__'] = old_signature
+                            else:
+                                del(new_options['__buildout_signature__'])
                     if old_options == new_options:
                         # The options are the same, but are all of the
                         # installed files still there?  If not, we should
@@ -1995,6 +2010,12 @@ Options:
     be uninstalled and what will be installed without doing anything
     in reality.
 
+  --skip-signature-check
+
+    Ignore __buildout_signature__ difference in comparing with the
+    previously installed state.
+
+
 Assignments are of the form: section:option=value and are used to
 provide configuration options that override those given in the
 configuration file.  For example, to run the buildout in offline mode,
@@ -2116,6 +2137,8 @@ def main(args=None):
 
             elif orig_op == '--dry-run':
                     options.append(('buildout', 'dry-run', 'true'))
+            elif orig_op == '--skip-signature-check':
+                    options.append(('buildout', 'check-signature', 'false'))
             elif op:
                 if orig_op == '--help':
                     _help()