`pyrefly report`: (re-)exports

[jorenham]

Typestats only considers public symbols for the stats. The way it determines whether a symbol is public, is by following all (re-)exports (__all__, or all non-private names if there's no __all__, and import a as a), and marking those as public.

For example:

# pkg/a.py
from ._b import _f
__all__ = ("_f",)

def g(): ...

Here, pkg._b._f is marked as public, but g is only marked public iff. it's publically re-exported in another public module.
With "public module" I mean one that's explicitly exported as public module, is called __init__ or __main__ and lives within a public package, or is a submodule of a public package with and has a non-private name (i.e. the module name does not start with _).

pyrefly report currently reports all symbols, and does not distinguish between public/private. AFAIK that's perfectly fine.
However, for typestats, I'll have to detemrine when it's public. And for that I need to know the export graph, which I can't determine by looking at the pyrefly report at the moment. To be precise, for each module, I need to know which symbols it exports. I can figure that out if I know:

• the statically evaluated __all__ names (so after "flattening" operations like += and .append)
• the import {name} as {name} implicit re-exports (also if there's an __all__)

If there is no __all__, then I can piece together the public names by looking at the namesof the module in the report json.
Note that I need to be able to distinguish between a module with an __all__ = () and a module that has no __all__.

Would that be possible to include in pyrefly report?

It's not part of typestats report, but that's because those reports already only show the public symbols.