[ty] Don't warn yield not in function when yield is in function (#18008)

crates/ty_python_semantic/resources/mdtest/diagnostics/semantic_syntax_errors.md

@@ -298,25 +298,25 @@ python-version = "3.12"
 ```
 
 ```py
-# error: [invalid-type-form] "`yield` expressions are not allowed in type expressions"
-# error: [invalid-syntax] "yield expression cannot be used within a TypeVar bound"
-# error: [invalid-syntax] "`yield` statement outside of a function"
-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 TypeVar bound"
+    type X[T: (yield 1)] = int
 
-# error: [invalid-type-form] "`yield` expressions are not allowed in type expressions"
-# error: [invalid-syntax] "yield expression cannot be used within a type alias"
-# error: [invalid-syntax] "`yield` statement outside of a function"
-type Y = (yield 1)
+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)
 
 # error: [invalid-type-form] "Named expressions are not allowed in type expressions"
 # error: [invalid-syntax] "named expression cannot be used within a generic definition"
 def f[T](x: int) -> (y := 3):
     return x
 
-# error: [invalid-syntax] "`yield from` statement outside of a function"
-# error: [invalid-syntax] "yield expression cannot be used within a generic definition"
-class C[T]((yield from [object])):
-    pass
+def _():
+    # error: [invalid-syntax] "yield expression cannot be used within a generic definition"
+    class C[T]((yield from [object])):
+        pass
 ```
 
 ## `await` outside async function

crates/ty_python_semantic/src/semantic_index/builder.rs

@@ -2481,6 +2481,18 @@ impl SemanticSyntaxContext for SemanticIndexBuilder<'_> {
         false
     }
 
+    fn in_yield_allowed_context(&self) -> bool {
+        for scope_info in self.scope_stack.iter().rev() {
+            let scope = &self.scopes[scope_info.file_scope_id];
+            match scope.kind() {
+                ScopeKind::Class | ScopeKind::Comprehension => return false,
+                ScopeKind::Function | ScopeKind::Lambda => return true,
+                ScopeKind::Module | ScopeKind::TypeAlias | ScopeKind::Annotation => {}
+            }
+        }
+        false
+    }
+
     fn in_sync_comprehension(&self) -> bool {
         for scope_info in self.scope_stack.iter().rev() {
             let scope = &self.scopes[scope_info.file_scope_id];