gh-107972: Argument Clinic: Ensure a C basename is provided after 'as'

Lib/test/test_clinic.py

@@ -28,7 +28,8 @@ def _make_clinic(*, filename='clinic_tests'):
     return c
 
 
-def _expect_failure(tc, parser, code, errmsg, *, filename=None, lineno=None):
+def _expect_failure(tc, parser, code, errmsg, *, filename=None, lineno=None,
+                    strip=True):
     """Helper for the parser tests.
 
     tc: unittest.TestCase; passed self in the wrapper
@@ -38,7 +39,9 @@ def _expect_failure(tc, parser, code, errmsg, *, filename=None, lineno=None):
     filename: str, optional filename
     lineno: int, optional line number
     """
-    code = dedent(code).strip()
+    code = dedent(code)
+    if strip:
+        code = code.strip()
     errmsg = re.escape(errmsg)
     with tc.assertRaisesRegex(clinic.ClinicError, errmsg) as cm:
         parser(code)
@@ -828,9 +831,10 @@ def parse_function(self, text, signatures_in_block=2, function_index=1):
         assert isinstance(s[function_index], clinic.Function)
         return s[function_index]
 
-    def expect_failure(self, block, err, *, filename=None, lineno=None):
+    def expect_failure(self, block, err, *,
+                       filename=None, lineno=None, strip=True):
         return _expect_failure(self, self.parse_function, block, err,
-                               filename=filename, lineno=lineno)
+                               filename=filename, lineno=lineno, strip=strip)
 
     def checkDocstring(self, fn, expected):
         self.assertTrue(hasattr(fn, "docstring"))
@@ -1491,6 +1495,16 @@ def test_illegal_c_basename(self):
         err = "Illegal C basename: '935'"
         self.expect_failure(block, err)
 
+    def test_no_c_basename(self):
+        block = "foo as "
+        err = "No C basename provided after 'as' keyword"
+        self.expect_failure(block, err, strip=False)
+
+    def test_no_c_basename_cloned(self):
+        block = "foo as = foo2"
+        err = "No C basename provided after 'as' keyword"
+        self.expect_failure(block, err)
+
     def test_single_star(self):
         block = """
             module foo

Tools/clinic/clinic.py

@@ -4864,9 +4864,11 @@ def state_modulename_name(self, line: str) -> None:
         before, equals, existing = line.rpartition('=')
         c_basename: str | None
         if equals:
-            full_name, _, c_basename = before.partition(' as ')
+            full_name, _as, c_basename = before.partition(' as ')
             full_name = full_name.strip()
             c_basename = c_basename.strip()
+            if _as and not c_basename:
+                fail("No C basename provided after 'as' keyword")
             existing = existing.strip()
             if (is_legal_py_identifier(full_name) and
                 (not c_basename or is_legal_c_identifier(c_basename)) and
@@ -4916,10 +4918,11 @@ def state_modulename_name(self, line: str) -> None:
         line, _, returns = line.partition('->')
         returns = returns.strip()
 
-        full_name, _, c_basename = line.partition(' as ')
+        full_name, _as, c_basename = line.partition(' as ')
         full_name = full_name.strip()
         c_basename = c_basename.strip() or None
-
+        if _as and not c_basename:
+            fail("No C basename provided after 'as' keyword")
         if not is_legal_py_identifier(full_name):
             fail(f"Illegal function name: {full_name!r}")
         if c_basename and not is_legal_c_identifier(c_basename):