fix: Fix frame lookup for Python 3.12 annotation scopes

guppylang/engine.py

@@ -100,6 +100,17 @@ def register_impl(self, ty_id: DefId, name: str, impl_id: DefId) -> None:
             frame = self.frames[impl_id].f_back
             if frame:
                 self.frames[impl_id] = frame
+                # For Python 3.12 generic functions and classes, there is an additional
+                # inserted frame for the annotation scope. We can detect this frame by
+                # looking for the special ".generic_base" variable in the frame locals
+                # that is implicitly inserted by CPython. See
+                # - https://docs.python.org/3/reference/executionmodel.html#annotation-scopes
+                # - https://docs.python.org/3/reference/compound_stmts.html#generic-functions
+                # - https://jellezijlstra.github.io/pep695.html
+                if ".generic_base" in frame.f_locals:
+                    frame = frame.f_back
+                    assert frame is not None
+                    self.frames[impl_id] = frame
 
 
 DEF_STORE: DefinitionStore = DefinitionStore()

tests/integration/test_poly_py312.py

@@ -28,6 +28,24 @@ def main(s: MyStruct[int, float]) -> float:
     validate(guppy.compile(main))
 
 
+def test_inner_frame(validate):
+    """See https://github.com/CQCL/guppylang/issues/1116"""
+    def make():
+        @guppy.struct
+        class MyStruct[T]:
+            @guppy
+            def foo(self: "MyStruct[int]") -> None:
+                pass
+
+        @guppy
+        def main() -> None:
+            MyStruct[int]().foo()
+
+        return main
+
+    validate(guppy.compile(make()))
+
+
 def test_copy_bound(validate):
     @guppy.struct
     class MyStruct[T: Copy]: