[ty] fix global symbol lookup from eager scopes

[mtshiba]

Summary

cf. #20962

In the following code, foo in the comprehension was not reported as unresolved:

# error: [unresolved-reference] "Name `foo` used when not defined"
foo
foo = [
    # no error!
    # revealed: Divergent
    reveal_type(x) for _ in () for x in [foo]
]

baz = [
    # error: [unresolved-reference] "Name `baz` used when not defined"
    # revealed: Unknown
    reveal_type(x) for _ in () for x in [baz]
]

In fact, this is a more serious bug than it looks: for foo, explicit_global_symbol is called, causing a symbol that should actually be Undefined to be reported as being of type Divergent.

This PR fixes this bug. As a result, the code in mdtest/regression/pr_20962_comprehension_panics.md no longer panics.

Test Plan

corpus\cyclic_symbol_in_comprehension.py is added.
New tests are added in mdtest/comprehensions/basic.md.

[github-actions]

Diagnostic diff on typing conformance tests

No changes detected when running ty on typing conformance tests ✅

[github-actions]

mypy_primer results

No ecosystem changes detected ✅

Memory usage changes were detected when running on open source projects

trio (https://github.com/python-trio/trio)
- WARN expected `heap_size` to be provided by Salsa query `GenericAlias < 'db >::variance_of_`
+ WARN expected `heap_size` to be provided by Salsa query `ClassLiteral < 'db >::variance_of_`
- WARN expected `heap_size` to be provided by Salsa query `GenericAlias < 'db >::variance_of_`
+ WARN expected `heap_size` to be provided by Salsa query `ClassLiteral < 'db >::variance_of_`
- WARN expected `heap_size` to be provided by Salsa query `GenericAlias < 'db >::variance_of_`
+ WARN expected `heap_size` to be provided by Salsa query `ClassLiteral < 'db >::variance_of_`
- WARN expected `heap_size` to be provided by Salsa query `GenericAlias < 'db >::variance_of_`
+ WARN expected `heap_size` to be provided by Salsa query `ClassLiteral < 'db >::variance_of_`
- WARN expected `heap_size` to be provided by Salsa query `GenericAlias < 'db >::variance_of_`
+ WARN expected `heap_size` to be provided by Salsa query `ClassLiteral < 'db >::variance_of_`
- WARN expected `heap_size` to be provided by Salsa query `GenericAlias < 'db >::variance_of_`
+ WARN expected `heap_size` to be provided by Salsa query `ClassLiteral < 'db >::variance_of_`
- WARN expected `heap_size` to be provided by Salsa query `GenericAlias < 'db >::variance_of_`
+ WARN expected `heap_size` to be provided by Salsa query `ClassLiteral < 'db >::variance_of_`
- WARN expected `heap_size` to be provided by Salsa query `GenericAlias < 'db >::variance_of_`
+ WARN expected `heap_size` to be provided by Salsa query `ClassLiteral < 'db >::variance_of_`
- WARN expected `heap_size` to be provided by Salsa query `GenericAlias < 'db >::variance_of_`
+ WARN expected `heap_size` to be provided by Salsa query `ClassLiteral < 'db >::variance_of_`
+ WARN expected `heap_size` to be provided by Salsa query `ClassLiteral < 'db >::variance_of_`
+ WARN expected `heap_size` to be provided by Salsa query `ClassLiteral < 'db >::variance_of_`

sphinx (https://github.com/sphinx-doc/sphinx)
- WARN expected `heap_size` to be provided by Salsa query `ClassLiteral < 'db >::variance_of_`
+ WARN expected `heap_size` to be provided by Salsa query `GenericAlias < 'db >::variance_of_`
- WARN expected `heap_size` to be provided by Salsa query `ClassLiteral < 'db >::variance_of_`
+ WARN expected `heap_size` to be provided by Salsa query `GenericAlias < 'db >::variance_of_`
- WARN expected `heap_size` to be provided by Salsa query `ClassLiteral < 'db >::variance_of_`
- WARN expected `heap_size` to be provided by Salsa query `ClassLiteral < 'db >::variance_of_`
- WARN expected `heap_size` to be provided by Salsa query `ClassLiteral < 'db >::variance_of_`
- WARN expected `heap_size` to be provided by Salsa query `ClassLiteral < 'db >::variance_of_`
- WARN expected `heap_size` to be provided by Salsa query `ClassLiteral < 'db >::variance_of_`
- WARN expected `heap_size` to be provided by Salsa query `ClassLiteral < 'db >::variance_of_`
- WARN expected `heap_size` to be provided by Salsa query `ClassLiteral < 'db >::variance_of_`
- WARN expected `heap_size` to be provided by Salsa query `ClassLiteral < 'db >::variance_of_`
- WARN expected `heap_size` to be provided by Salsa query `ClassLiteral < 'db >::variance_of_`
- WARN expected `heap_size` to be provided by Salsa query `ClassLiteral < 'db >::variance_of_`

prefect (https://github.com/PrefectHQ/prefect)
+ WARN expected `heap_size` to be provided by Salsa query `ClassLiteral < 'db >::variance_of_`
- WARN expected `heap_size` to be provided by Salsa query `GenericAlias < 'db >::variance_of_`
- WARN expected `heap_size` to be provided by Salsa query `GenericAlias < 'db >::variance_of_`
- WARN expected `heap_size` to be provided by Salsa query `GenericAlias < 'db >::variance_of_`
- WARN expected `heap_size` to be provided by Salsa query `GenericAlias < 'db >::variance_of_`
- WARN expected `heap_size` to be provided by Salsa query `GenericAlias < 'db >::variance_of_`
- WARN expected `heap_size` to be provided by Salsa query `GenericAlias < 'db >::variance_of_`
- WARN expected `heap_size` to be provided by Salsa query `GenericAlias < 'db >::variance_of_`
- WARN expected `heap_size` to be provided by Salsa query `GenericAlias < 'db >::variance_of_`
- WARN expected `heap_size` to be provided by Salsa query `GenericAlias < 'db >::variance_of_`

[mtshiba]

ty_server::e2e pull_diagnostics::document_diagnostic_caching_changed seems to hang non-deterministically.

https://github.com/astral-sh/ruff/actions/runs/19173434027/job/54811898939?pr=21317

[carljm]

If returning here is correct, then pushing the constraint into constraint_keys immediately above this cannot have any effect, so should we remove that as well? (Removing it doesn't seem to fail any test.)

Why do we hit the FoundConstraint case in this situation in the first place? It's not clear to me where the "constraint" comes from.

[mtshiba]

Since place includes member as well as symbol, narrowing constraints must still be tracked even if there are no bindings, for example:

from typing import Literal

class Foo:
    bar: Literal[1, 2]

foo = Foo()
if foo.bar == 1:
    # `foo.bar` has no explicit binding, but the constraint is `foo.bar == 1`
    [reveal_type(foo.bar) for _ in ()]  # Literal[1]

But as you pointed out, there was no need to add the constraint to constraint_keys here, because we already added it when iterating over ancestor_scopes above. Fixed.