[PATCH 1 of 2] py3: protect from exceptions thrown by other meta-path finders

[Yuya Nishihara]

On Mon, 22 Apr 2019 21:22:31 -0400, Ludovic Chabant wrote:
> >
> > Is there any list of exceptions that are known to be safely
> > suppressed? Catching AttributeError, TypeError, etc. seems bad.
> >
> 
> In my case, it's just a missing method so AttributeError is what's being
> raised I think (see
> https://github.com/benjaminp/six/blob/master/six.py#L164).
> 
> My rationale here was that there could be any 3rd party finder in there,
> so it might make sense to protect Mercurial from crashing because of
> exceptions thrown from other packages.
> 
> However, now that I think about it, another maybe more correct way to
> fix this specific bug might be to check for `find_spec` and, if missing,
> call `find_module` instead. As per the Python docs (see
> https://docs.python.org/3/library/importlib.html#importlib.abc.MetaPathFinder),
> the latter was deprecated in 3.4, the former is new in 3.4. So my guess
> is that _SixMetaPathImporter uses the old API so that it's compatible
> with all versions of Python 3 (as Python probably does this fallback on
> the old API if the new doesn't exist).
> 
> Would that be better?

Sounds good to me.

CC indygreg as he should know the importer API better.