[3.9] gh-91583: AC: Fix regression for functions with defining_class (GH-91739) (GH-92080)

Argument Clinic now generates the same efficient code as before
adding the defining_class parameter.
(cherry picked from commit a055dac)

Author: serhiy-storchaka

Misc/NEWS.d/next/Tools-Demos/2022-04-20-14-26-14.gh-issue-91583.200qI0.rst

@@ -0,0 +1,2 @@
+Fix regression in the code generated by Argument Clinic for functions with
+the ``defining_class`` parameter.

Modules/clinic/_testmultiphase.c.h

@@ -636,6 +636,10 @@ def output_templates(self, f):
         assert parameters
         assert isinstance(parameters[0].converter, self_converter)
         del parameters[0]
+        requires_defining_class = False
+        if parameters and isinstance(parameters[0].converter, defining_class_converter):
+            requires_defining_class = True
+            del parameters[0]
         converters = [p.converter for p in parameters]
 
         has_option_groups = parameters and (parameters[0].group or parameters[-1].group)
@@ -657,10 +661,6 @@ def output_templates(self, f):
                 if not p.is_optional():
                     min_pos = i
 
-        requires_defining_class = any(
-            isinstance(p.converter, defining_class_converter)
-            for p in parameters)
-
         meth_o = (len(parameters) == 1 and
               parameters[0].is_positional_only() and
               not converters[0].is_optional() and
@@ -763,24 +763,40 @@ def parser_body(prototype, *fields, declarations=''):
             return linear_format(output(), parser_declarations=declarations)
 
         if not parameters:
-            # no parameters, METH_NOARGS
+            if not requires_defining_class:
+                # no parameters, METH_NOARGS
+                flags = "METH_NOARGS"
 
-            flags = "METH_NOARGS"
+                parser_prototype = normalize_snippet("""
+                    static PyObject *
+                    {c_basename}({self_type}{self_name}, PyObject *Py_UNUSED(ignored))
+                    """)
+                parser_code = []
 
-            parser_prototype = normalize_snippet("""
-                static PyObject *
-                {c_basename}({self_type}{self_name}, PyObject *Py_UNUSED(ignored))
-                """)
-            parser_definition = parser_prototype
+            else:
+                assert not new_or_init
 
-            if default_return_converter:
-                parser_definition = parser_prototype + '\n' + normalize_snippet("""
-                    {{
-                        return {c_basename}_impl({impl_arguments});
+                flags = "METH_METHOD|METH_FASTCALL|METH_KEYWORDS"
+
+                parser_prototype = parser_prototype_def_class
+                return_error = ('return NULL;' if default_return_converter
+                                else 'goto exit;')
+                parser_code = [normalize_snippet("""
+                    if (nargs) {{
+                        PyErr_SetString(PyExc_TypeError, "{name}() takes no arguments");
+                        %s
                     }}
-                    """)
+                    """ % return_error, indent=4)]
+
+            if default_return_converter:
+                parser_definition = '\n'.join([
+                    parser_prototype,
+                    '{{',
+                    *parser_code,
+                    '    return {c_basename}_impl({impl_arguments});',
+                    '}}'])
             else:
-                parser_definition = parser_body(parser_prototype)
+                parser_definition = parser_body(parser_prototype, *parser_code)
 
         elif meth_o:
             flags = "METH_O"
@@ -939,6 +955,9 @@ def parser_body(prototype, *fields, declarations=''):
 
             add_label = None
             for i, p in enumerate(parameters):
+                if isinstance(p.converter, defining_class_converter):
+                    raise ValueError("defining_class should be the first "
+                                     "parameter (after self)")
                 displayname = p.get_displayname(i+1)
                 parsearg = p.converter.parse_arg(argname_fmt % i, displayname)
                 if parsearg is None: