hgext3rd/__init__.py

packaging: support building WiX installers with PyOxidizer

We initially implemented PyOxidizer support for Inno installers.
That did most of the heavy work of integrating PyOxidizer into
the packaging system. Implementing WiX installer support was
pretty straightforward.

Aspects of this patch look very similar to Inno's.

The main difference is the handling of the Visual C++
Redistributable Runtime files.

The WiX installer was formerly using merge modules to
install the VC++ 9.0 runtime because this feature is
supported by the WiX installer (it isn't easily available
to Inno installers).

Our strategy for the runtime files is to install the
vcruntime140.dll file next to hg.exe just like any other
file. While we could leverage WiX's functionality for invoking
a VCRedist installer, I don't want to deal with the complexity
at this juncture. So, we let run_pyoxidizer() copy vcruntime140.dll
into the staging directory (like it does for Inno) and our
dynamic WiX XML generator picks it up as a regular file and
installs it.

We did, however, have to teach mercurial.wxs how to conditionally
use the merge modules. But this was rather straightforward.

Comparing the file layout of the WiX installers before and
after:

* Various lib/*.{pyd, dll} files no longer exist
* python27.dll was replaced by python37.dll
* vcruntime140.dll was added

All these changes are expected due to the transition to
Python 3 and to PyOxidizer, which embeded the .pyd and .dll files
in hg.exe.

Differential Revision: https://phab.mercurial-scm.org/D8477

# name space package to host third party extensions
from __future__ import absolute_import
import pkgutil

__path__ = pkgutil.extend_path(__path__, __name__)