Special case long_description_content_type

As described in the pypa pull request, special-case passing through
these fields into the metadata.  setuptools will maintain them.

Change-Id: I89eb8c6d627790680a61a0a4b7490191b6e8e90c
Closes-Bug: #1762494

doc/source/user/features.rst

@@ -181,6 +181,10 @@ probably a good long_description. So we'll just inject the contents of your
 You can also specify the exact file you want to use using the
 ``description-file`` parameter.
 
+You can set the ``description-content-type`` to a MIME type that may
+help rendering of the description; for example ``text/markdown`` or
+``text/x-rst; charset=UTF-8``.
+
 Requirements
 ~~~~~~~~~~~~
 

pbr/core.py

@@ -103,6 +103,16 @@ def pbr(dist, attr, value):
         raise errors.DistutilsSetupError(
             'Error parsing %s: %s: %s' % (path, e.__class__.__name__, e))
 
+
+    # There are some metadata fields that are only supported by
+    # setuptools and not distutils, and hence are not in
+    # dist.metadata.  We are OK to write these in.  For gory details
+    # see
+    #  https://github.com/pypa/setuptools/pull/1343
+    _DISTUTILS_UNSUPPORTED_METADATA = (
+        'long_description_content_type', 'project_urls', 'provides_extras'
+    )
+
     # Repeat some of the Distribution initialization code with the newly
     # provided attrs
     if attrs:
@@ -115,6 +125,8 @@ def pbr(dist, attr, value):
                 setattr(dist.metadata, key, val)
             elif hasattr(dist, key):
                 setattr(dist, key, val)
+            elif key in _DISTUTILS_UNSUPPORTED_METADATA:
+                setattr(dist.metadata, key, val)
             else:
                 msg = 'Unknown distribution option: %s' % repr(key)
                 warnings.warn(msg)

releasenotes/notes/long-descr-content-type-f9a1003acbb8740f.yaml

@@ -0,0 +1,6 @@
+---
+fixes:
+  - |
+    The ``description-content-type`` was not being set correctly.  It
+    will now be correctly populated when using ``setuptools`` 39.2.0
+    and beyond.