[mypyc] Make some generated classes implicitly final (#19235)

Classes used for generators, async functions and nested functions are
now final. This may slightly improve performance when using separate
compilation.

Author: JukkaL

mypyc/irbuild/callable_class.py

@@ -55,7 +55,7 @@ class for the nested function.
     # Define the actual callable class ClassIR, and set its
     # environment to point at the previously defined environment
     # class.
-    callable_class_ir = ClassIR(name, builder.module_name, is_generated=True)
+    callable_class_ir = ClassIR(name, builder.module_name, is_generated=True, is_final_class=True)
 
     # The functools @wraps decorator attempts to call setattr on
     # nested functions, so we create a dict for these nested

mypyc/irbuild/env_class.py

@@ -43,7 +43,10 @@ class is generated, the function environment has not yet been
     containing a nested function.
     """
     env_class = ClassIR(
-        f"{builder.fn_info.namespaced_name()}_env", builder.module_name, is_generated=True
+        f"{builder.fn_info.namespaced_name()}_env",
+        builder.module_name,
+        is_generated=True,
+        is_final_class=True,
     )
     env_class.attributes[SELF_NAME] = RInstance(env_class)
     if builder.fn_info.is_nested:

mypyc/irbuild/generator.py

@@ -155,7 +155,7 @@ def instantiate_generator_class(builder: IRBuilder) -> Value:
 def setup_generator_class(builder: IRBuilder) -> ClassIR:
     name = f"{builder.fn_info.namespaced_name()}_gen"
 
-    generator_class_ir = ClassIR(name, builder.module_name, is_generated=True)
+    generator_class_ir = ClassIR(name, builder.module_name, is_generated=True, is_final_class=True)
     if builder.fn_info.can_merge_generator_and_env_classes():
         builder.fn_info.env_class = generator_class_ir
     else: