nit: I'd probably just wrap this in an outer function to suppress these outside of a function errors since we only intend to test the other errors here. I think a lot of other mdtests use a function named _ to indicate this:

def _():
    type X[T: (yield 1)] = int

but it's not a huge deal.

I think there is still something here. With

def _():
# error: [invalid-type-form] "`yield` expressions are not allowed in type expressions"
# error: [invalid-syntax] "yield expression cannot be used within a TypeVar bound"
    type X[T: (yield 1)] = int

def _():
# error: [invalid-type-form] "`yield` expressions are not allowed in type expressions"
# error: [invalid-syntax] "yield expression cannot be used within a type alias"
    type Y = (yield 1)

I still get the outside of a function errors

semantic_syntax_errors.md - Semantic syntax error diagnostics - Invalid expression

  crates/ty_python_semantic/resources/mdtest/diagnostics/semantic_syntax_errors.md:304 unexpected error: 16 [invalid-syntax] "`yield` statement outside of a function"
  crates/ty_python_semantic/resources/mdtest/diagnostics/semantic_syntax_errors.md:309 unexpected error: 15 [invalid-syntax] "`yield` statement outside of a function"

Ah, that's a bug, thank you! We can merge this as is, and I'll tackle it in a follow-up.

If you're curious, ty has separate scope kinds for type aliases and annotations, so the check for function scope needs to skip those instead of just checking that the immediate scope is a function. At least that looks like the easy fix to me.

This doesn't necessarily need to block this PR since you're just reporting the current state of things, but we might need to open a follow-up issue here to avoid duplicate diagnostics. @AlexWaygood do you know if the type error is separate from the syntax error here, or should we only pick one of these to emit?

I talked to Alex, and this is a symptom of a more general need to suppress type-checking errors when there are syntax errors present. I'll spin off an issue for this too, so no worries here.

The issue already exists in the ty repo! astral-sh/ty#119