updated after some feedback from distutils-SIG and MAL

pep-0390.txt

@@ -62,6 +62,24 @@ fields. If an option that corresponds to a Metadata field is given to
 ``setup()``, it will override the value that was possibly present in
 ``setup.cfg``.
 
+Notice that ``setup.py`` is still used and can be required to define some
+options that are not part of the Metadata fields. For instance, the
+``sdist`` command can use options like ``packages`` or ``scripts``.
+
+
+Multi-lines values
+==================
+
+Some Metadata fields can have multiple values. To keep ``setup.cfg`` compatible
+with ``ConfigParser`` and the RFC 822 ``LONG HEADER FIELDS`` (see section 3.1.1),
+these are expressed with ``,``-separated values::
+
+    requires = pywin32, bar > 1.0, foo
+
+When this variable is read, the values are parsed and transformed into a list:
+``['pywin32', 'bar > 1.0', 'foo']``.
+
+
 Context-dependant sections
 ==========================
 
@@ -75,8 +93,8 @@ environment. Here's some examples::
    version = 0.6.4
 
    [metadata:sys_platform == 'win32']
-   requires = pywin32
+   requires = pywin32, bar > 1.0
-   requires = bar > 1.0
+   obsoletes = pywin31
 
    [metadata:os_machine == 'i386']
    requires = foo
@@ -107,11 +125,14 @@ where ``EXPR`` belongs to any of those:
 - python_version = '%s.%s' % (sys.version_info[0], sys.version_info[1])
 - os_name = os.name
 - sys_platform = sys.platform
-- os_version = os.uname()[3]
+- platform_version = platform.version()
-- os_machine = os.uname()[4]
+- platform_machine = platform.machine()
 - a free string, like ``2.4``, or ``win32``
 
-Distutils will provide a function that is able to read the metadata
+Notice that ``in`` is restricted to strings, meaning that it is not possible
+to use other sequences like tuples or lists on the left side.
+
+Distutils will provide a function that is able to generate the metadata
 of a distribution, given a ``setup.cfg`` file, for the execution environment::
 
    >>> from distutils.util import local_metadata
@@ -121,11 +142,66 @@ of a distribution, given a ``setup.cfg`` file, for the execution environment::
 This means that a vanilla Python will be able to read the metadata of a
 package without running any third party code.
 
+Notice that this feature is not restricted to the ``metadata`` namespace.
+Consequently, any other section can be extended with such context-dependant
+sections.
+
+Impact on PKG-INFO generation and PEP 314
+=========================================
+
+When ``PKG-INFO`` is generated by Distutils, every field that relies on a
+condition will have that condition written at the end of the line, after a `;`
+separator::
+
+    Metadata-Version: 1.2
+    Name: distribute
+    Version: 0.6.4
+    ...
+    Requires: pywin32, bar > 1.0; sys_platform == 'win32'
+    Requires: foo; os_machine == 'i386'
+    Requires: bar; python_version == '2.4' or python_version == '2.5'
+    Requires: baz; 'linux' in sys_platform
+    Obsoletes = pywin31; sys_platform == 'win32'
+    ...
+    Classifier: Development Status :: 5 - Production/Stable
+    Classifier: Intended Audience :: Developers
+    Classifier: License :: OSI Approved :: Python Software Foundation License
+
+Notice that this file can be opened with the ``DistributionMetadata`` class.
+This class will be able to use the micro-language using the execution
+environment.
+
+Let's run in on a ``Python 2.5 i386 Linux``::
+
+    >>> from distutils.dist import DistributionMetadata
+    >>> metadata = DistributionMetadata('PKG_INFO')
+    >>> metadata.get_requires()
+    ['foo', 'bar', 'baz']
+
+The execution environment can be overriden in case we want to get the meyadata
+for another environment::
+
+    >>> env = {'python_version': '2.4',
+    ...        'os_name': 'nt',
+    ...        'sys_platform': 'win32',
+    ...        'platform_version': 'MVCC++ 6.0'
+    ...        'platform_machine': 'i386'}
+    ...
+    >>> metadata = DistributionMetadata('PKG_INFO', environment=env)
+    >>> metadata.get_requires()
+    ['bar > 1.0', 'foo', 'bar']
+
+PEP 314 is changed accordingly, meaning that each field will be able to
+have that extra condition marker.
+
 Compatiblity
 ============
 
-This change is fully backward compatible since it just adds a section in the
+This change is is based on a new metadata ``1.2`` format meaning that
-``ConfigParser``-compatible ``setup.cfg`` file.
+Distutils will be able to distinguish old PKG-INFO files from new ones.
+
+The ``setup.cfg`` file change will stay ``ConfigParser``-compatible and
+will not break existing ``setup.cfg`` files.
 
 Limitations
 ===========