Write .installed.cfg in safe way and only if there's any change.

Also, updating a part does not put it anymore at the end of the list of
installed parts, that was making .installed.cfg too big.

src/zc/buildout/buildout.py

@@ -32,6 +32,7 @@ from cStringIO import StringIO
 import copy
 import datetime
 import distutils.errors
+import errno
 import glob
 import itertools
 import logging
@@ -173,6 +174,12 @@ def _print_annotate(data):
                     line = '   '
     print_()
 
+def _remove_ignore_missing(path):
+    try:
+        os.remove(path)
+    except OSError, e:
+        if e.errno != errno.ENOENT:
+            raise
 
 def _unannotate_section(section):
     for key in section:
@@ -642,10 +649,6 @@ class Buildout(DictMixin):
         installed_part_options['buildout']['installed_develop_eggs'
                                            ] = installed_develop_eggs
 
-        if installed_exists:
-            self._update_installed(
-                installed_develop_eggs=installed_develop_eggs)
-
         # get configured and installed part lists
         conf_parts = self['buildout']['parts']
         conf_parts = conf_parts and conf_parts.split() or []
@@ -719,7 +722,9 @@ class Buildout(DictMixin):
             installed_parts = [p for p in installed_parts if p != part]
 
             if installed_exists:
-                self._update_installed(parts=' '.join(installed_parts))
+                installed_part_options['buildout']['parts'] = (
+                    ' '.join(installed_parts))
+                self._save_installed_options(installed_part_options)
 
         # Check for unused buildout options:
         _check_for_unused_options_in_section(self, 'buildout')
@@ -730,7 +735,6 @@ class Buildout(DictMixin):
             saved_options = self[part].copy()
             recipe = self[part].recipe
             if part in installed_parts: # update
-                need_to_save_installed = False
                 __doing__ = 'Updating %s.', part
                 self._logger.info(*__doing__)
                 old_options = installed_part_options[part]
@@ -747,12 +751,12 @@ class Buildout(DictMixin):
 
                 try:
                     installed_files = self[part]._call(update)
-                except:
+                except Exception:
                     installed_parts.remove(part)
                     self._uninstall(old_installed_files)
-                    if installed_exists:
-                        self._update_installed(
-                            parts=' '.join(installed_parts))
+                    installed_part_options['buildout']['parts'] = (
+                        ' '.join(installed_parts))
+                    self._save_installed_options(installed_part_options)
                     raise
 
                 old_installed_files = old_installed_files.split('\n')
@@ -764,16 +768,7 @@ class Buildout(DictMixin):
                     else:
                         installed_files = list(installed_files)
 
-                    need_to_save_installed = [
-                        p for p in installed_files
-                        if p not in old_installed_files]
-
-                    if need_to_save_installed:
-                        installed_files = (old_installed_files
-                                           + need_to_save_installed)
-
             else: # install
-                need_to_save_installed = True
                 __doing__ = 'Installing %s.', part
                 self._logger.info(*__doing__)
                 installed_files = self[part]._call(recipe.install)
@@ -797,33 +792,18 @@ class Buildout(DictMixin):
             installed_parts.append(part)
             _check_for_unused_options_in_section(self, part)
 
-            if need_to_save_installed:
-                installed_part_options['buildout']['parts'] = (
-                    ' '.join(installed_parts))
-                self._save_installed_options(installed_part_options)
-                installed_exists = True
-            else:
-                assert installed_exists
-                self._update_installed(parts=' '.join(installed_parts))
+            installed_part_options['buildout']['parts'] = (
+                ' '.join(installed_parts))
+            self._save_installed_options(installed_part_options)
 
-        if installed_develop_eggs:
-            if not installed_exists:
-                self._save_installed_options(installed_part_options)
-        elif (not installed_parts) and installed_exists:
-            os.remove(self['buildout']['installed'])
+        installed_part_options['buildout']['parts'] = (
+            ' '.join(installed_parts))
+        self._save_installed_options(installed_part_options)
 
         if self.show_picked_versions or self.update_versions_file:
             self._print_picked_versions()
         self._unload_extensions()
 
-    def _update_installed(self, **buildout_options):
-        installed = self['buildout']['installed']
-        f = open(installed, 'a')
-        f.write('\n[buildout]\n')
-        for option, value in list(buildout_options.items()):
-            _save_option(option, value, f)
-        f.close()
-
     def _uninstall_part(self, part, installed_part_options):
         # uninstall part
         __doing__ = 'Uninstalling %s.', part
@@ -990,12 +970,35 @@ class Buildout(DictMixin):
         installed = self['buildout']['installed']
         if not installed:
             return
-        f = open(installed, 'w')
-        _save_options('buildout', installed_options['buildout'], f)
-        for part in installed_options['buildout']['parts'].split():
-            print_(file=f)
-            _save_options(part, installed_options[part], f)
-        f.close()
+        buildout = installed_options['buildout']
+        installed_parts = buildout['parts'].split()
+        if installed_parts or buildout['installed_develop_eggs']:
+            new = StringIO()
+            buildout['parts'] = ' '.join(installed_parts)
+            _save_options('buildout', buildout, new)
+            for part in installed_parts:
+                print >>new
+                _save_options(part, installed_options[part], new)
+            new = new.getvalue()
+            try:
+                with open(installed) as f:
+                    save = f.read(1+len(new)) != new
+            except IOError, e:
+                if e.errno != errno.ENOENT:
+                    raise
+                save = True
+            if save:
+                installed_tmp = installed + ".tmp"
+                try:
+                    with open(installed_tmp, "w") as f:
+                        f.write(new)
+                        f.flush()
+                        os.fsync(f.fileno())
+                    os.rename(installed_tmp, installed)
+                finally:
+                    _remove_ignore_missing(installed_tmp)
+        else:
+            _remove_ignore_missing(installed)
 
     def _error(self, message, *args):
         raise zc.buildout.UserError(message % args)