gh-153849: Expose scope attributes on symtable entries

[serhiy-storchaka]

The symbol table analysis computes a number of per-scope attributes that the compiler relies on, but did not expose them. Add read-only attributes to the low-level symbol table entries: is_generator, is_coroutine, has_annotations, has_conditional_annotations, needs_class_closure, needs_classdict, can_see_class_scope and annotation_block.

Attributes that are trivially derivable from the AST (such as whether a function has a *args parameter) are deliberately not included; they can be added later.

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• Issue: symtable entries should expose the scope attributes computed by the analysis #153849

[JelleZijlstra]

This is exposing private implementation details of the compiler that we might want to change later. What would the backward compatibility implications be if we want to (for example) get rid of can_see_class_scope in a later version?

[serhiy-storchaka]

First of all, this attributes are added to a class in private module _symtable. It is not even documented. Public module symtable wraps it in other other class which does not expose these attributes.

Currently I am playing with Python implementation of the compiler. None of these attributes are essential, they can be derived from the AST, and the first version of the compiler did it. But they are not trivially derivable. Exposing them in _symtable makes the code simpler. These attributes are needed for the C compiler, we cannot simply get rid of them. If we can get rid of them, this implies serious semantic changes in Python language. If the C compiler no longer need them, then outer tools do not need them either.

[JelleZijlstra]

OK, if this stays limited to a private module I have no concerns.