Adjust function literal return type inference to avoid spurious null

Author: eernstg

resources/type-system/inference.md

@@ -6,6 +6,11 @@ Status: Draft
 
 ## CHANGELOG
 
+2024.12.17
+  - Change the function literal return type inference rules to ignore
+    `return;` statements in generators (it doesn't actually cause null to be
+    returned).
+
 2022.05.12
   - Define the notions of "constraint solution for a set of type variables" and
     "Grounded constraint solution for a set of type variables".  These
@@ -324,7 +329,8 @@ schema.
     `e`, using the local type inference algorithm described below with typing
     context `K`, and update `T` to be `UP(flatten(S), T)` if the enclosing
     function is `async`, or `UP(S, T)` otherwise.
-  - For each `return;` statement in the block, update `T` to be `UP(Null, T)`.
+  - If the enclosing function is not marked `sync*` or `async*`: For each
+    `return;` statement in the block, update `T` to be `UP(Null, T)`.
   - For each `yield e;` statement in the block, let `S` be the inferred type of
     `e`, using the local type inference algorithm described below with typing
     context `K`, and update `T` to be `UP(S, T)`.