use incremental to canonicalize versions for release

CONTRIBUTING.rst

@@ -30,19 +30,19 @@ Step-by-step
 - Define the final release version you are preparing.
 
   - towncrier uses `CalVer <https://calver.org/>`_ of the form ``YY.MM.micro`` with the micro version just incrementing.
-  - Normalize the version according to `PEP 440 <https://www.python.org/dev/peps/pep-0440/#normalization>`_.
+  - Normalize the version according to `incremental <https://github.com/twisted/incremental/>`_.
 
     - This requires that ``towncrier[dev]`` extra is installed.
     - ``venv/bin/python admin/canonicalize_version.py 19.09.00-rc1``
-    - Outputs ``19.9rc1`` which is the form to be used.
+    - Outputs ``19.9.0.rc1`` which is the form to be used.
 
-- Create a release branch with a name of the form ``release-19.9`` starting from the ``master`` branch.
+- Create a release branch with a name of the form ``release-19.9.0`` starting from the ``master`` branch.
 
   - On the new release branch you will commit all tagged release candidate commits as well as the final tagged release commit.
 
 - Update the version to the release candidate with the first being ``rc1`` (as opposed to 0).
 
-  - In ``src/towncrier/_version.py`` the version is set using ``incremental`` such as ``__version__ = Version('towncrier', 19, 9, release_candidate=1)``
+  - In ``src/towncrier/_version.py`` the version is set using ``incremental`` such as ``__version__ = Version('towncrier', 19, 9, 0, release_candidate=1)``
 
 - Run ``venv/bin/towncrier build --yes`` to build the the newsfragments into the release notes document and to automatically remove the newsfragment files.
 
@@ -54,7 +54,7 @@ Step-by-step
 
 - Request a review and address raised concerns until receiving an approval.
 
-- Tag that commit such as ``19.9rc1`` and push the tag to the primary repository.
+- Tag that commit such as ``19.9.0.rc1`` and push the tag to the primary repository.
 
   - This will result in another build which will publish to PyPI.
   - Confirm the presence of the release on PyPI.
@@ -73,7 +73,7 @@ Step-by-step
 
 - If ready for a final release, remove the release candidate indicator from the version.
 
-  - Edit ``src/towncrier/_version.py`` such as ``__version__ = Version('towncrier', 19, 9)`` to remove the release candidate indication.
+  - Edit ``src/towncrier/_version.py`` such as ``__version__ = Version('towncrier', 19, 9, 0)`` to remove the release candidate indication.
 
   - Return to the towncrier build step and continue.
 

admin/canonicalize_version.py

@@ -1,14 +1,31 @@
 import click
+import incremental
 import packaging.utils
 
 
 @click.command()
 @click.argument("version")
 def cli(version):
-    """Canonicalizes the passed version according to PEP 517."""
-    canonicalized_version = packaging.utils.canonicalize_version(version)
+    """Canonicalizes the passed version according to incremental."""
 
-    click.echo(canonicalized_version)
+    parsed_version = packaging.utils.Version(version)
+
+    release_candidate = None
+    if parsed_version.pre is not None:
+        if parsed_version.pre[0] == 'rc':
+            release_candidate = parsed_version.pre[1]
+
+    incremental_version = incremental.Version(
+        package="",
+        major=parsed_version.major,
+        minor=parsed_version.minor,
+        micro=parsed_version.micro,
+        release_candidate=release_candidate,
+        post=parsed_version.post,
+        dev=parsed_version.dev,
+    )
+
+    click.echo(incremental_version.public())
 
 
 if __name__ == "__main__":

src/towncrier/newsfragments/329.misc.rst

@@ -0,0 +1 @@
+