From 83721b7d758dd8d7548823bad8225f29609d78ae Mon Sep 17 00:00:00 2001
From: Stan Ulbrych <stan@python.org>
Date: Tue, 6 Oct 2026 20:57:30 +0200
Subject: [PATCH 1/2] Make Argument Clinic exit with an error if a warning was
 emitted

---
 Tools/clinic/libclinic/cli.py    | 11 ++++++++---
 Tools/clinic/libclinic/errors.py | 10 ++++++++++
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/Tools/clinic/libclinic/cli.py b/Tools/clinic/libclinic/cli.py
index 9629c173177945..f7a8022a24d54f 100644
--- a/Tools/clinic/libclinic/cli.py
+++ b/Tools/clinic/libclinic/cli.py
@@ -12,7 +12,7 @@
 
 # Local imports.
 import libclinic
-import libclinic.cpp
+import libclinic.errors
 from libclinic import ClinicError
 from libclinic.language import Language, PythonLanguage
 from libclinic.block_parser import BlockParser
@@ -340,10 +340,15 @@ def run_clinic(parser: argparse.ArgumentParser, ns: argparse.Namespace) -> None:
 def main(argv: list[str] | None = None) -> NoReturn:
     parser = create_cli()
     args = parser.parse_args(argv)
+    libclinic.errors.reset_warning_count()
     try:
         run_clinic(parser, args)
     except ClinicError as exc:
         sys.stderr.write(exc.report())
         sys.exit(1)
-    else:
-        sys.exit(0)
+    count = libclinic.errors.warning_count
+    if count:
+        noun = "warning" if count == 1 else "warnings"
+        sys.stderr.write(f"{count} {noun} emitted\n")
+        sys.exit(1)
+    sys.exit(0)
diff --git a/Tools/clinic/libclinic/errors.py b/Tools/clinic/libclinic/errors.py
index f06bdfbd864b2c..d17c9a5a7050b5 100644
--- a/Tools/clinic/libclinic/errors.py
+++ b/Tools/clinic/libclinic/errors.py
@@ -27,6 +27,14 @@ class ParseError(ClinicError):
     pass
 
 
+warning_count = 0
+
+
+def reset_warning_count() -> None:
+    global warning_count
+    warning_count = 0
+
+
 @overload
 def warn_or_fail(
     *args: object,
@@ -54,6 +62,8 @@ def warn_or_fail(
     if fail:
         raise error
     else:
+        global warning_count
+        warning_count += 1
         print(error.report(warn_only=True))
 
 

From 52d30c52c014f869de7345d3765e817a0b65e2ba Mon Sep 17 00:00:00 2001
From: Stan Ulbrych <stan@python.org>
Date: Tue, 6 Oct 2026 21:30:03 +0200
Subject: [PATCH 2/2] Add test

---
 Lib/test/test_clinic.py | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/Lib/test/test_clinic.py b/Lib/test/test_clinic.py
index 3b440fed7f6ce8..16004b002f8ba3 100644
--- a/Lib/test/test_clinic.py
+++ b/Lib/test/test_clinic.py
@@ -3739,6 +3739,23 @@ def test_no_change(self):
         # if the content does not change
         self.assertEqual(pre_mtime, post_mtime)
 
+    def test_warning_is_failure(self):
+        code = dedent("""
+            /*[clinic input]
+            @permit_long_summary
+            fn
+
+            Short summary.
+            [clinic start generated code]*/
+        """)
+        with os_helper.temp_dir() as tmp_dir:
+            fn = os.path.join(tmp_dir, "test.c")
+            with open(fn, "w", encoding="utf-8") as f:
+                f.write(code)
+            out, err = self.expect_failure(fn)
+        self.assertIn("Remove the @permit_long_summary decorator from 'fn'!", out)
+        self.assertEqual(err, "1 warning emitted\n")
+
     TOUCH_CODE = dedent("""
         /*[clinic input]
         module m