[mypyc] Fixing condition for handling user-defined __del__ (#19188)

Fixes #19175.

Conditions for generating and invoking `del` method were not consistent.

As things currently stand, this pull request fixes the crash. However, for classes that derive from Python built-ins, user-defined `__del__` will not be invoked.

Author: advait-dixit

mypyc/codegen/emitclass.py

@@ -304,9 +304,6 @@ def emit_line() -> None:
         emit_line()
         generate_dealloc_for_class(cl, dealloc_name, clear_name, bool(del_method), emitter)
         emit_line()
-        if del_method:
-            generate_finalize_for_class(del_method, finalize_name, emitter)
-            emit_line()
 
         if cl.allow_interpreted_subclasses:
             shadow_vtable_name: str | None = generate_vtables(
@@ -317,6 +314,9 @@ def emit_line() -> None:
             shadow_vtable_name = None
         vtable_name = generate_vtables(cl, vtable_setup_name, vtable_name, emitter, shadow=False)
         emit_line()
+    if del_method:
+        generate_finalize_for_class(del_method, finalize_name, emitter)
+        emit_line()
     if needs_getseters:
         generate_getseter_declarations(cl, emitter)
         emit_line()

mypyc/test-data/run-classes.test

@@ -2754,6 +2754,21 @@ def test_function():
     assert(isinstance(d.fitem, ForwardDefinedClass))
     assert(isinstance(d.fitems, ForwardDefinedClass))
 
+[case testDelForDictSubclass-xfail]
+# The crash in issue mypy#19175 is fixed.
+# But, for classes that derive from built-in Python classes, user-defined __del__ method is not
+# being invoked.
+class DictSubclass(dict):
+    def __del__(self):
+        print("deleting DictSubclass...")
+
+[file driver.py]
+import native
+native.DictSubclass()
+
+[out]
+deleting DictSubclass...
+
 [case testDel]
 class A:
     def __del__(self):
@@ -2774,6 +2789,12 @@ class C(B):
 class D(A):
     pass
 
+# Just make sure that this class compiles (see issue mypy#19175). testDelForDictSubclass tests for
+# correct output.
+class NormDict(dict):
+    def __del__(self) -> None:
+        pass
+
 [file driver.py]
 import native
 native.C()