Fix a bug in $$ escape handling.

That caused uninstall and install everytime for a part containing $$ in its saved options.
Also it caused broken .installed.cfg in case of error, like the referenced section was not defined.

src/zc/buildout/buildout.py

@@ -702,7 +702,7 @@ class Buildout(DictMixin):
             if part in install_parts:
                 old_options = self.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.get(
                         '__buildout_signature__', None)
@@ -957,7 +957,7 @@ class Buildout(DictMixin):
                         for k, v in _spacey_defaults:
                             value = value.replace(k, v)
                         options[option] = value
-                result[section] = self.Options(self, section, options)
+                result[section] = self.Options(self, section, options).copy()
 
             return result
         else:

src/zc/buildout/buildout.txt

@@ -2135,6 +2135,7 @@ changes, the service shouldn't be changed.
     >>> print_(system(buildout), end='')
     Develop: '/sample-buildout/recipes'
     Updating service.
+    Unused options for service: 'script'.
 
 Now we change the service part to trigger uninstallation and
 re-installation.

src/zc/buildout/tests.py

@@ -1007,6 +1007,7 @@ Uninstall recipes need to be called when a part is removed too:
     uninstalling
     Installing demo.
     installing
+    Unused options for demo: 'x'.
 
 
     >>> write('buildout.cfg', '''

[Julien Muchembled]

Issues:

• Why the change _read_installed_part_options ?
• The new "Unused options" warning in src/zc/buildout/tests.py is a nice side-effect, but not the other: in fact, such warning is irrelevant when updating a part.
• check-signature option does not work anymore.

So I would only keep the change in src/zc/buildout/tests.py and do:

--- a/src/zc/buildout/buildout.py
+++ b/src/zc/buildout/buildout.py
@@ -735,6 +735,7 @@ def install(self, install_args):
                                 new_options['__buildout_signature__'] = old_signature
                             else:
                                 del(new_options['__buildout_signature__'])
+                    new_options = new_options.copy()
                     if old_options == new_options:
                         # The options are the same, but are all of the
                         # installed files still there?  If not, we should
@@ -821,9 +822,9 @@ def install(self, install_args):
                 saved_options['__buildout_installed__'] = installed_files
                 saved_options['__buildout_signature__'] = signature
                 installed_part_options[part] = saved_options
-                part in installed_parts or installed_parts.append(part)
-
-                _check_for_unused_options_in_section(self, part)
+                if part not in installed_parts:
+                    installed_parts.append(part)
+                    _check_for_unused_options_in_section(self, part)
 
         finally:
             installed_path = self['buildout']['installed']

[Julien Muchembled]

Fixed in branch 1.x as described above