[PATCH 3 of 5 RFC] policy: add helper to import cpy/pure module selectively

[Gregory Szorc]

On Sat, Aug 13, 2016 at 3:15 AM, Yuya Nishihara <yuya at tcha.org> wrote:

> # HG changeset patch
> # User Yuya Nishihara <yuya at tcha.org>
> # Date 1470969017 -32400
> #      Fri Aug 12 11:30:17 2016 +0900
> # Node ID 8bb0a9223bce791bae9e6a07238d6b9722e5577a
> # Parent  bda4422fc315b54356ba1949e5ba861dd2660e86
> policy: add helper to import cpy/pure module selectively
>
> Unfortunately, __import__() nor getattr() does not take bytes, and
> globals()
> is a dict keyed by unicodes on Python 3. uimportvars() is a unicode API to
> comply with their requirement. I really hated mixing bytes and unicodes,
> but
> bytes version of importvars() would be useless.
>
> Nit: KeyError would be raised for invalid HGMODULEPOLICY. What should we
> do in that case?
>

We have precedence for this in the `hg` script: we write an untranslated
abort message
to sys.stderr and call sys.exit. Ideally we would translate that message.
But without
a module load policy, that gets difficult. We would probably ideally change
the policy to
"pure" (since that will always work), load i18n.py, then do a normal abort.
But to do that
may require moving some policy loading code into __init__.py.


>
> diff --git a/mercurial/policy.py b/mercurial/policy.py
> --- a/mercurial/policy.py
> +++ b/mercurial/policy.py
> @@ -23,6 +23,14 @@ policy = 'c'
>  policynoc = ('cffi', 'cffi-allow', 'py')
>  policynocffi = ('c', 'py')
>
> +_upackagetable = {
> +    'c': [u'cpy'],
> +    'allow': [u'cpy', u'pure'],
> +    'cffi': [u'pure'],  # TODO: [u'cffi']
> +    'cffi-allow': [u'pure'],  # TODO: [u'cffi', u'pure']
> +    'py': [u'pure'],
> +}
> +
>  try:
>      from . import __modulepolicy__
>      policy = __modulepolicy__.modulepolicy
> @@ -43,3 +51,24 @@ if sys.version_info[0] >= 3:
>
>  # Environment variable can always force settings.
>  policy = os.environ.get('HGMODULEPOLICY', policy)
> +
> +def _uexportedvars(mod):
> +    """Build dict of public names to simulate 'from mod import *'"""
> +    modvars = vars(mod)
> +    if u'__all__' in modvars:
> +        allnames = modvars[u'__all__']
> +        return dict((k, v) for k, v in modvars.items() if k in allnames)
> +    return dict((k, v) for k, v in modvars.items() if not
> k.startswith(u'_'))
> +
> +def uimportvars(uname):
> +    """Import module according to policy and return exported vars"""
> +    upkgnames = _upackagetable[policy]
> +    for upkg in upkgnames:
> +        try:
> +            # pass globals() to resolve name relative to this module
> +            mod = __import__(u'%s.%s' % (upkg, uname), globals(), level=1)
> +            mod = getattr(mod, uname)
> +            return _uexportedvars(mod)
> +        except ImportError:
> +            if upkg == upkgnames[-1]:
> +                raise
>

The "u" prefixing feels a bit weird. Your commit message says the bytes
version of "importvars" would be useless. So why the prefix?
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