gh-110907: AC: Disallow using * with vararg

Lib/test/test_clinic.py

@@ -359,6 +359,20 @@ def __init__(self):
         """
         self.expect_failure(block, err, lineno=8)
 
+    def test_multiple_star_in_args(self):
+        err = "'my_test_func' uses '*' more than once."
+        block = """
+            /*[clinic input]
+            my_test_func
+
+                pos_arg: object
+                *args: object
+                *
+                kw_arg: object
+            [clinic start generated code]*/
+        """
+        self.expect_failure(block, err, lineno=6)
+
     def test_module_already_got_one(self):
         err = "Already defined module 'm'!"
         block = """

Objects/typevarobject.c

@@ -327,7 +327,6 @@ typevar.__new__ as typevar_new
 
     name: object(subclass_of="&PyUnicode_Type")
     *constraints: object
-    *
     bound: object = None
     covariant: bool = False
     contravariant: bool = False
@@ -340,7 +339,7 @@ static PyObject *
 typevar_new_impl(PyTypeObject *type, PyObject *name, PyObject *constraints,
                  PyObject *bound, int covariant, int contravariant,
                  int infer_variance)
-/*[clinic end generated code: output=1d200450ee99226d input=2c07ab87c94f462b]*/
+/*[clinic end generated code: output=1d200450ee99226d input=41ae33a916bfe76f]*/
 {
     if (covariant && contravariant) {
         PyErr_SetString(PyExc_ValueError,

Tools/clinic/clinic.py

@@ -5944,6 +5944,7 @@ def parse_star(self, function: Function, version: VersionTuple | None) -> None:
         if version is None:
             if self.keyword_only:
                 fail(f"Function {function.name!r} uses '*' more than once.")
+            self.check_previous_star()
             self.check_remaining_star()
             self.keyword_only = True
         else:
@@ -6353,6 +6354,14 @@ def check_remaining_star(self, lineno: int | None = None) -> None:
         fail(f"Function {self.function.name!r} specifies {symbol!r} "
              f"without following parameters.", line_number=lineno)
 
+    def check_previous_star(self, lineno: int | None = None) -> None:
+        assert isinstance(self.function, Function)
+
+        for p in self.function.parameters.values():
+            if p.kind == inspect.Parameter.VAR_POSITIONAL:
+                fail(f"Function {self.function.name!r} uses '*' more than once.")
+
+
     def do_post_block_processing_cleanup(self, lineno: int) -> None:
         """
         Called when processing the block is done.