gh-107880: Argument Clinic: Fix regression in gh-107885 (#107974)

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

Lib/test/test_clinic.py

@@ -609,6 +609,35 @@ def test_directive_output_invalid_command(self):
         """
         self.expect_failure(block, err, lineno=2)
 
+    def test_validate_cloned_init(self):
+        block = """
+            /*[clinic input]
+            class C "void *" ""
+            C.meth
+              a: int
+            [clinic start generated code]*/
+            /*[clinic input]
+            @classmethod
+            C.__init__ = C.meth
+            [clinic start generated code]*/
+        """
+        err = "'__init__' must be a normal method, not a class or static method"
+        self.expect_failure(block, err, lineno=8)
+
+    def test_validate_cloned_new(self):
+        block = """
+            /*[clinic input]
+            class C "void *" ""
+            C.meth
+              a: int
+            [clinic start generated code]*/
+            /*[clinic input]
+            C.__new__ = C.meth
+            [clinic start generated code]*/
+        """
+        err = "'__new__' must be a class method"
+        self.expect_failure(block, err, lineno=7)
+
 
 class ParseFileUnitTest(TestCase):
     def expect_parsing_failure(
@@ -1918,7 +1947,7 @@ class Foo "" ""
             self.parse_function(block)
 
     def test_new_must_be_a_class_method(self):
-        err = "__new__ must be a class method!"
+        err = "'__new__' must be a class method!"
         block = """
             module foo
             class Foo "" ""
@@ -1927,7 +1956,7 @@ class Foo "" ""
         self.expect_failure(block, err, lineno=2)
 
     def test_init_must_be_a_normal_method(self):
-        err = "__init__ must be a normal method, not a class or static method!"
+        err = "'__init__' must be a normal method, not a class or static method!"
         block = """
             module foo
             class Foo "" ""
@@ -2030,7 +2059,7 @@ def test_illegal_c_identifier(self):
         self.expect_failure(block, err, lineno=2)
 
     def test_cannot_convert_special_method(self):
-        err = "__len__ is a special method and cannot be converted"
+        err = "'__len__' is a special method and cannot be converted"
         block = """
             class T "" ""
             T.__len__

Tools/clinic/clinic.py

@@ -4840,6 +4840,21 @@ def state_dsl_start(self, line: str) -> None:
 
         self.next(self.state_modulename_name, line)
 
+    def update_function_kind(self, fullname: str) -> None:
+        fields = fullname.split('.')
+        name = fields.pop()
+        _, cls = self.clinic._module_and_class(fields)
+        if name in unsupported_special_methods:
+            fail(f"{name!r} is a special method and cannot be converted to Argument Clinic!")
+        if name == '__new__':
+            if (self.kind is not CLASS_METHOD) or (not cls):
+                fail("'__new__' must be a class method!")
+            self.kind = METHOD_NEW
+        elif name == '__init__':
+            if (self.kind is not CALLABLE) or (not cls):
+                fail("'__init__' must be a normal method, not a class or static method!")
+            self.kind = METHOD_INIT
+
     def state_modulename_name(self, line: str) -> None:
         # looking for declaration, which establishes the leftmost column
         # line should be
@@ -4888,6 +4903,7 @@ def state_modulename_name(self, line: str) -> None:
                 function_name = fields.pop()
                 module, cls = self.clinic._module_and_class(fields)
 
+                self.update_function_kind(full_name)
                 overrides: dict[str, Any] = {
                     "name": function_name,
                     "full_name": full_name,
@@ -4948,20 +4964,9 @@ def state_modulename_name(self, line: str) -> None:
         function_name = fields.pop()
         module, cls = self.clinic._module_and_class(fields)
 
-        fields = full_name.split('.')
-        if fields[-1] in unsupported_special_methods:
-            fail(f"{fields[-1]} is a special method and cannot be converted to Argument Clinic!  (Yet.)")
-
-        if fields[-1] == '__new__':
-            if (self.kind is not CLASS_METHOD) or (not cls):
-                fail("__new__ must be a class method!")
-            self.kind = METHOD_NEW
-        elif fields[-1] == '__init__':
-            if (self.kind is not CALLABLE) or (not cls):
-                fail("__init__ must be a normal method, not a class or static method!")
-            self.kind = METHOD_INIT
-            if not return_converter:
-                return_converter = init_return_converter()
+        self.update_function_kind(full_name)
+        if self.kind is METHOD_INIT and not return_converter:
+            return_converter = init_return_converter()
 
         if not return_converter:
             return_converter = CReturnConverter()