Merge pull request #524 from meejah/2942.towncrier-draft

add a 'draftnews' tox environment

newsfragments/2942.feature

@@ -0,0 +1 @@
+Add a "tox -e draftnews" which runs towncrier in draft mode

towncrier.pyproject.toml

@@ -1,6 +1,6 @@
 [tool.towncrier]
-    package = "allmydata"
     package_dir = "src"
+    package = "allmydata"
     filename = "NEWS.rst"
     directory = "newsfragments"
     start_string = ".. towncrier start line"

tox.ini

@@ -98,6 +98,32 @@ commands =
 	 # file.  See pyproject.toml for legal <change type> values.
 	 python -m towncrier.check
 
+[testenv:draftnews]
+passenv = TAHOE_LAFS_* PIP_* SUBUNITREPORTER_* USERPROFILE HOMEDRIVE HOMEPATH
+# see comment in [testenv] about "certifi"
+whitelist_externals = mv
+deps =
+     certifi
+     towncrier >= 19.2
+commands =
+         # With pip >= 10 the existence of pyproject.toml (which we are
+         # required to have to configure towncrier) triggers a "build
+         # isolation" mode which prevents anything from working.  Avoid
+         # triggering that pip behavior by keeping the towncrier configuration
+         # somewhere else and only bringing it in when it's actually needed
+         # (after pip is done).
+         #
+         # Some discussion is available at
+         # https://github.com/pypa/pip/issues/5696
+         mv towncrier.pyproject.toml pyproject.toml
+
+         # towncrier 19.2 + works with python2.7
+         python -m towncrier --draft
+
+         # put it back
+         mv pyproject.toml towncrier.pyproject.toml
+
+
 [testenv:deprecations]
 setenv =
          PYTHONWARNINGS=default::DeprecationWarning