[PATCH 12 of 12 RFC] policy: add helper to import cext/pure module

[Yuya Nishihara]

On Tue, 9 May 2017 11:08:03 -0700, Jun Wu wrote:
> > > Patch 12 is where I disagree. _dualmod still requires careful renaming and
> > > could cause subtle problems that does not get warned by any code checking
> > > tools. They also require extra effort in writing and reviewing related code.
> > > I'd like to go through the explicit versioning way so even the renaming
> > > churn could be avoided.
> > > 
> > > [1]: https://www.mercurial-scm.org/pipermail/mercurial-devel/2017-May/097329.html 
> > 
> > I'm okay for the explicit versioning. I can adjust the last patch for that.
> > 
> > I don't have strong preference since managing API versions would be as
> > simple as managing explicit version constants unless we have internal
> > dependency in C layer.
> 
> We do have complex cases: module-level exception (mpatch.mpatchError), and
> parsers.c with complex Python objects. Think about if someone wants to catch
> mpatchError, or change the return value of lmiter_iterkeysnext in manifest.c
> for example.

Yeah, I know. My opinion is that I won't care much about that as we don't
right now. FWIW, mpatchError isn't exported by the C module.

That said, there seems no objection to switching to the per-module versioning,
so maybe we can go for it.