pythongh-106359: Fix corner case bugs in Argument Clinic converter parser (python#106361)

DSLParser.parse_converter() could return unusable kwdicts in some rare cases

Co-authored-by: Alex Waygood <[email protected]>

Author: erlend-aasland

Lib/test/test_clinic.py

@@ -813,6 +813,22 @@ def test_other_bizarre_things_in_annotations_fail(self):
         )
         self.assertEqual(s, expected_failure_message)
 
+    def test_kwarg_splats_disallowed_in_function_call_annotations(self):
+        expected_error_msg = (
+            "Error on line 0:\n"
+            "Cannot use a kwarg splat in a function-call annotation\n"
+        )
+        dataset = (
+            'module fo\nfo.barbaz\n   o: bool(**{None: "bang!"})',
+            'module fo\nfo.barbaz -> bool(**{None: "bang!"})',
+            'module fo\nfo.barbaz -> bool(**{"bang": 42})',
+            'module fo\nfo.barbaz\n   o: bool(**{"bang": None})',
+        )
+        for fn in dataset:
+            with self.subTest(fn=fn):
+                out = self.parse_function_should_fail(fn)
+                self.assertEqual(out, expected_error_msg)
+
     def test_unused_param(self):
         block = self.parse("""
             module foo

Misc/NEWS.d/next/Tools-Demos/2023-07-03-14-06-19.gh-issue-106359.RfJuR0.rst

@@ -0,0 +1,2 @@
+Argument Clinic now explicitly forbids "kwarg splats" in function calls used as
+annotations.

Tools/clinic/clinic.py

@@ -4291,6 +4291,7 @@ def dedent(self, line):
 
 
 StateKeeper = Callable[[str | None], None]
+ConverterArgs = dict[str, Any]
 
 class DSLParser:
     function: Function | None
@@ -5033,21 +5034,22 @@ def bad_node(self, node):
         key = f"{parameter_name}_as_{c_name}" if c_name else parameter_name
         self.function.parameters[key] = p
 
-    KwargDict = dict[str | None, Any]
-
     @staticmethod
-    def parse_converter(annotation: ast.expr | None) -> tuple[str, bool, KwargDict]:
+    def parse_converter(
+            annotation: ast.expr | None
+    ) -> tuple[str, bool, ConverterArgs]:
         match annotation:
             case ast.Constant(value=str() as value):
                 return value, True, {}
             case ast.Name(name):
                 return name, False, {}
             case ast.Call(func=ast.Name(name)):
                 symbols = globals()
-                kwargs = {
-                    node.arg: eval_ast_expr(node.value, symbols)
-                    for node in annotation.keywords
-                }
+                kwargs: ConverterArgs = {}
+                for node in annotation.keywords:
+                    if not isinstance(node.arg, str):
+                        fail("Cannot use a kwarg splat in a function-call annotation")
+                    kwargs[node.arg] = eval_ast_expr(node.value, symbols)
                 return name, False, kwargs
             case _:
                 fail(