Evan Wilde d99e3318db Add implementation of _unavailableFromAsync check ...

The core part of the check runs as follows
 1. Are we in an async context
 2. Does the decl we're calling have the unavailableFromAsync attribute
 3. Emit a diagnostic

There are a couple challenges that muddy the implementation. First,
single-expression closures are typechecked differently than
multi-expression closures. The single-expression closure is never added
to the closure stack. We have to record it separately upon entry to
verify separately. This is necessary for `_ = { foo() }()` where `foo`
is unavailable from async, and the surrounding context is async.

The second challenge is regarding when things get typechecked. A type
must be assigned to AbstractClosureExprs to determine whether they are
an async context or not. Unfortunately, availability checking runs
before types are fully assigned in some cases. This specifically happens
when working with result builders in specific conditions. I haven't been
able to figure out how to reduce the issue further.

2021-11-30 14:20:21 -08:00

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UnderscoredAttributes.md

Add implementation of _unavailableFromAsync check

2021-11-30 14:20:21 -08:00