py3: manually import pycompat.open into files that need it...
py3: manually import pycompat.open into files that need it
We want to eliminate the source transformer. Currently it inserts
a `from mercurial.pycompat import ...` at the top of files to alias
some builtins.
This commit replaces the implicit import of `open` with an explicit
import on files that need it and changes the source transformer to
no longer import `open`.
As part of this, we needed to store an explicit local for `open` in
the Python 2 code path in `pycompat` so the import works. (Builtins
that are automatically in scope cannot be imported.)
Differential Revision:
https://phab.mercurial-scm.org/D7005
