Add 'dry_run' option (-d) and 'ignore __buildout_signature__ difference' option (-S).

src/zc/buildout/buildout.py

@@ -219,6 +219,8 @@ _buildout_default_options = _annotate_section({
     'log-level': 'INFO',
     'newest': 'true',
     'offline': 'false',
+    'dry_run': 'false',
+    'check_signature': 'true',
     'parts-directory': 'parts',
     'prefer-final': 'false',
     'python': 'buildout',
@@ -328,6 +330,8 @@ class Buildout(UserDict.DictMixin):
         self._logger = logging.getLogger('zc.buildout')
         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')
 
@@ -705,7 +709,16 @@ class Buildout(UserDict.DictMixin):
                 if part in install_parts:
                     old_options = installed_part_options[part].copy()
                     installed_files = old_options.pop('__buildout_installed__')
-                    new_options = self.get(part)
+                    new_options = self.get(part).copy()
+                    if not self.check_signature:
+                        old_signature = old_options.pop(
+                            '__buildout_signature__', None)
+                        new_signature = new_options.pop(
+                            '__buildout_signature__', None)
+                        if old_signature != new_signature:
+                            self._logger.info(
+                                '[%s]: __buildout_signature__ is different '
+                                'but ignored.' % part)
                     if old_options == new_options:
                         # The options are the same, but are all of the
                         # installed files still there?  If not, we should
@@ -750,6 +763,8 @@ class Buildout(UserDict.DictMixin):
                 if part in installed_parts: # update
                     __doing__ = 'Updating %s.', part
                     self._logger.info(*__doing__)
+                    if self.dry_run:
+                        continue
                     old_options = installed_part_options[part]
                     old_installed_files = old_options['__buildout_installed__']
 
@@ -775,6 +790,8 @@ class Buildout(UserDict.DictMixin):
                 else: # install
                     __doing__ = 'Installing %s.', part
                     self._logger.info(*__doing__)
+                    if self.dry_run:
+                        continue
                     installed_files = self[part]._call(recipe.install)
                     if installed_files is None:
                         self._logger.warning(
@@ -794,7 +811,9 @@ class Buildout(UserDict.DictMixin):
 
         finally:
             installed_path = self['buildout']['installed']
-            if installed_parts:
+            if self.dry_run:
+                pass
+            elif installed_parts:
                 new = StringIO()
                 buildout = installed_part_options['buildout']
                 buildout['parts'] = ' '.join(installed_parts)
@@ -830,6 +849,8 @@ class Buildout(UserDict.DictMixin):
         # uninstall part
         __doing__ = 'Uninstalling %s.', part
         self._logger.info(*__doing__)
+        if self.dry_run:
+            return
 
         # run uninstall recipe
         recipe, entry = _recipe(installed_part_options[part])
@@ -1959,6 +1980,17 @@ Options:
     Squelch warnings about using an executable with a broken -S
     implementation.
 
+  -d
+
+    Dry-run mode.  With this setting, buildout will display what will
+    be uninstalled and what will be installed without doing anything
+    in reality.
+
+  -S
+
+    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,
@@ -2029,7 +2061,7 @@ def main(args=None):
         if args[0][0] == '-':
             op = orig_op = args.pop(0)
             op = op[1:]
-            while op and op[0] in 'vqhWUoOnNDAs':
+            while op and op[0] in 'vqhWUoOnNDAsdS':
                 if op[0] == 'v':
                     verbosity += 10
                 elif op[0] == 'q':
@@ -2050,6 +2082,10 @@ def main(args=None):
                     debug = True
                 elif op[0] == 's':
                     ignore_broken_dash_s = True
+                elif op[0] == 'd':
+                    options.append(('buildout', 'dry_run', 'true'))
+                elif op[0] == 'S':
+                    options.append(('buildout', 'check_signature', 'false'))
                 else:
                     _help()
                 op = op[1:]