[WIP] Another stab at #88

[pavel-kirienko]

Disabling the Jinja cache results in the unique name generator state disappearing from the global Jinja context:

>       return _UniqueNameGenerator.ensure_generator_in_globals(env.globals)('c', adj_base_token, '_', '_')
E       TypeError: 'NoneType' object is not callable
.tox/py35-test/lib/python3.5/site-packages/nunavut/lang/c.py:527: TypeError

This issue affects all languages. The following test modification indicates that the state gets replaced with None:

------------------------- src/nunavut/lang/__init__.py -------------------------
index bd6524c..135a29a 100644
@@ -226,7 +226,7 @@ class _UniqueNameGenerator:
    def ensure_generator_in_globals(cls, environment_globals: typing.Dict[str, typing.Any]) -> '_UniqueNameGenerator':
        from .. import TypeLocalGlobalKey

-        if TypeLocalGlobalKey not in environment_globals:
+        if environment_globals.get(TypeLocalGlobalKey) is None:
            environment_globals[TypeLocalGlobalKey] = cls()
        return typing.cast('_UniqueNameGenerator', environment_globals[TypeLocalGlobalKey])

I don't quite understand what is happening and why it worked on my machine last week.

@thirtytwobits do you find the added test logic sensible?

[thirtytwobits]

So I rebased this on my PR and we do get past the None error but it still doesn't work the way you expect. I am uncertain that macros will have anything that isn't an argument reevaluated. For that you'll want to create another template and include it.

[thirtytwobits]

Closing as I merged this into #91 before tracking down the final problems with it.