gh-150097: Move _testclinic to multi-phase init

Convert the static types to heap types. Move empty init vectorcall to
share with existing no-arg __init__ case. Add support for no-argument
vectorcall so the no-arg __init__ cases actually work (rather than
adding an arg). Produce the same error string as the PyArg helpers do.

The vectorcall types no longer have a C address for the generated
`Py_Is` so instead compare the slot function instead. This drops the
requirement that a class using vectorcall declare a type object.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

(cherry-picked from #157968)

Author: cmaloney

Tools/clinic/libclinic/dsl_parser.py

@@ -639,11 +639,6 @@ def normalize_function_kind(self, fullname: str) -> None:
             if not self.kind.new_or_init:
                 fail("@vectorcall can only be used with __init__ and __new__ "
                      "methods currently")
-            # Guaranteed by the __new__ / __init__ checks above.
-            assert cls is not None
-            if not cls.type_object:
-                fail(f"@vectorcall requires the type object of {cls.name!r}, "
-                     f"which was declared without one")
 
     def resolve_return_converter(
         self, full_name: str, forced_converter: str

Tools/clinic/libclinic/parse_args.py

@@ -6,7 +6,7 @@
 from libclinic.function import (
     Function, Parameter, ParamTuple,
     count_required, group_to_variable_name, permute_optional_groups,
-    GETTER, SETTER, SETTER_AND_DELETER, METHOD_INIT,
+    GETTER, SETTER, SETTER_AND_DELETER, METHOD_INIT, METHOD_NEW,
     ACCESSORS, SETTERS)
 from libclinic.converter import CConverter
 from libclinic.converters import (
@@ -1537,19 +1537,22 @@ def create_template_dict(self) -> dict[str, str]:
         return d2
 
     def _vectorcall_type_check(self) -> list[str]:
-        """Assert `type` is the one type this vectorcall was generated for.
+        """Check dispatch function hasn't changed.
 
-        The generated code is only correct for that type: __init__ calls
-        tp_new with no arguments, then the impl.  tp_vectorcall is not
-        inherited, so subclasses never reach it; the assert catches C code
-        installing the function on a second type.
+        The generated code is only correct for a type whose tp_new / tp_init is
+        the parser this vectorcall shadows.
         """
         func = self.func
-        # The DSL parser rejects @vectorcall without a class and type object.
-        assert func.cls is not None
-        assert func.cls.type_object
+        if func.kind is METHOD_INIT:
+            check = f"_PyType_CAST(type)->tp_init == {func.c_basename}"
+        elif func.kind is METHOD_NEW:
+            check = f"_PyType_CAST(type)->tp_new == {func.c_basename}"
+        else:
+            raise AssertionError(
+                f"Unhandled function kind for vectorcall: {func.kind!r}"
+            )
         return [libclinic.normalize_snippet(f"""
-            assert(Py_Is(_PyType_CAST(type), {func.cls.type_object}));
+            assert({check});
             /* Make sure the type object is immutable: the generated
              * vectorcall doesn't deal e.g. with users reassigning __init__. */
             assert(PyType_HasFeature(_PyType_CAST(type), Py_TPFLAGS_IMMUTABLETYPE));
@@ -1689,18 +1692,35 @@ def parse_vectorcall_pos_or_kw(self) -> None:
         parser_code.extend(self._vectorcall_positional(arity_checked=True))
         self.vectorcall_body(*parser_code)
 
+    def parse_vectorcall_no_args(self) -> None:
+        """No keyword or positional arguments."""
+        parser_code = self._vectorcall_type_check()
+        self.codegen.add_include('pycore_modsupport.h',
+                                 '_PyArg_NoKwnames()')
+        parser_code.append(libclinic.normalize_snippet("""
+            if (nargs) {{
+                PyErr_SetString(PyExc_TypeError,
+                                "{name}() takes no positional arguments");
+                goto exit;
+            }}
+            if (!_PyArg_NoKwnames("{name}", kwnames)) {{
+                goto exit;
+            }}
+            """, indent=4))
+        self.vectorcall_body(*parser_code)
+
     def parse_vectorcall(self) -> None:
         """Generate the vectorcall entry point for __new__ / __init__.
 
         Dispatch to specific parser-code builders based on parameter shape.
         """
         # Branches ordered to mirror parse_args().  The DSL parser rejects
         # @vectorcall with optional groups, and METH_O never applies to
-        # __new__/__init__. They always have arguments.
+        # __new__/__init__.
         assert not self.has_option_groups()
         assert not self.use_meth_o()
         if not self.parameters and not self.varpos and not self.var_keyword:
-            raise NotImplementedError("No argument vectorcall")
+            self.parse_vectorcall_no_args()
         elif self.var_keyword is not None:
             self.parse_vectorcall_kw_required()
         elif self.pos_only == len(self.parameters):