Bug fixed:

  Option incrementing and decrementing didn't work for options
  specified on the command line.

CHANGES.txt

@@ -14,6 +14,9 @@ Bugs fixed:
   didn't work in the buildout section.
   https://bugs.launchpad.net/zc.buildout/+bug/420463
 
+- Option incrementing and decrementing didn't work for options
+  specified on the command line.
+
 1.4.0 (2009-08-26)
 ==================
 

src/zc/buildout/buildout.py

@@ -14,31 +14,30 @@
 """Buildout main script
 """
 
+from rmtree import rmtree
+try:
+    from hashlib import md5
+except ImportError:
+    # Python 2.4 and older
+    from md5 import md5
+
+import ConfigParser
+import copy
 import distutils.errors
+import glob
+import itertools
 import logging
 import os
+import pkg_resources
 import re
 import shutil
 import sys
 import tempfile
-import ConfigParser
 import UserDict
-import glob
-import copy
-
-
-import pkg_resources
 import zc.buildout
 import zc.buildout.download
 import zc.buildout.easy_install
 
-from rmtree import rmtree
-
-try:
-    from hashlib import md5
-except ImportError:
-    # Python 2.4 and older
-    from md5 import md5
 
 realpath = zc.buildout.easy_install.realpath
 
@@ -160,9 +159,14 @@ class Buildout(UserDict.DictMixin):
         else:
             base = None
 
-        override = dict((option, (value, 'COMMAND_LINE_VALUE'))
-                        for section, option, value in cloptions
-                        if section == 'buildout')
+
+        cloptions = dict(
+            (section, dict((option, (value, 'COMMAND_LINE_VALUE'))
+                           for (_, option, value) in v))
+            for (section, v) in itertools.groupby(sorted(cloptions),
+                                                  lambda v: v[0])
+            )
+        override = cloptions.get('buildout', {}).copy()
 
         # load user defaults, which override defaults
         if user_defaults:
@@ -178,11 +182,7 @@ class Buildout(UserDict.DictMixin):
                                 data['buildout'].copy(), override))
 
         # apply command-line options
-        for (section, option, value) in cloptions:
-            options = data.get(section)
-            if options is None:
-                options = data[section] = {}
-            options[option] = value, "COMMAND_LINE_VALUE"
+        _update(data, cloptions)
 
         self._annotated = copy.deepcopy(data)
         self._raw = _unannotate(data)

src/zc/buildout/tests.py

@@ -11,11 +11,6 @@
 # FOR A PARTICULAR PURPOSE.
 #
 ##############################################################################
-"""XXX short summary goes here.
-
-$Id$
-"""
-
 from zope.testing import doctest
 from zope.testing import renormalizing
 import os
@@ -2591,7 +2586,31 @@ def increment_buildout_options():
       recipe='zc.buildout:debug'
     """
 
+def increment_on_command_line():
+    r"""
+    >>> write('buildout.cfg', '''
+    ... [buildout]
+    ... parts = p1
+    ... x = 1
+    ... y = a
+    ...     b
+    ...
+    ... [p1]
+    ... recipe = zc.buildout:debug
+    ... foo = ${buildout:x} ${buildout:y}
+    ...
+    ... [p2]
+    ... <= p1
+    ... ''')
 
+    >>> print system(buildout+' buildout:parts+=p2 p1:foo+=bar'),
+    Installing p1.
+      foo='1 a\nb\nbar'
+      recipe='zc.buildout:debug'
+    Installing p2.
+      foo='1 a\nb\nbar'
+      recipe='zc.buildout:debug'
+    """
 
 ######################################################################