Add example test for stubgen/mypy error

Author: timohl

tests/CMakeLists.txt

@@ -170,6 +170,7 @@ set(PYBIND11_TEST_FILES
     test_stl
     test_stl_binders
     test_stubgen
+    test_stubgen_error
     test_tagbased_polymorphic
     test_thread
     test_type_caster_pyobject_ptr

tests/test_stubgen.py

@@ -2,30 +2,31 @@
 
 from pathlib import Path
 
-import pybind11_stubgen as stubgen
+import pybind11_stubgen
 from mypy import api
 
 from pybind11_tests import stubgen as m
 
 
 def test_stubgen(tmp_path: Path) -> None:
     assert m.add_int(1, 2) == 3
-
-    stubgen.main(
+    # Generate stub into temporary directory
+    pybind11_stubgen.main(
         [
             "pybind11_tests.stubgen",
             "-o",
             tmp_path.as_posix(),
         ]
     )
-    print(f"Stubgen output: {tmp_path.as_posix()}")
+    # Check stub file is generated and contains expected content
     stub_file = tmp_path / "pybind11_tests" / "stubgen.pyi"
     assert stub_file.exists()
     stub_content = stub_file.read_text()
     assert (
         "def add_int(a: typing.SupportsInt, b: typing.SupportsInt) -> int:"
         in stub_content
     )
+    # Run mypy on the generated stub file
     normal_report, error_report, exit_status = api.run([stub_file.as_posix()])
     print("Normal report:")
     print(normal_report)

tests/test_stubgen_error.cpp

@@ -0,0 +1,5 @@
+#include "pybind11_tests.h"
+
+TEST_SUBMODULE(stubgen_error, m) {
+    m.def("identity_capsule", [](py::capsule c) { return c; }, "c"_a);
+}

tests/test_stubgen_error.py

@@ -0,0 +1,46 @@
+from __future__ import annotations
+
+import sys
+from pathlib import Path
+
+import pybind11_stubgen
+import pytest
+from mypy import api
+
+from pybind11_tests import stubgen_error as m
+
+
+@pytest.mark.skipif(
+    sys.version_info >= (3, 13), reason="CapsuleType available in 3.13+"
+)
+def test_stubgen(tmp_path: Path, caplog: pytest.LogCaptureFixture) -> None:
+    """Show stubgen/mypy errors for CapsuleType (not available in Python < 3.13)."""
+    assert m.identity_capsule(None) is None
+    # Generate stub into temporary directory
+    pybind11_stubgen.main(
+        [
+            "pybind11_tests.stubgen_error",
+            "-o",
+            tmp_path.as_posix(),
+        ]
+    )
+    # Errors are reported using logging
+    assert "Can't find/import 'types.CapsuleType'" in caplog.text
+    # Stub file is still generated if error is not fatal
+    stub_file = tmp_path / "pybind11_tests" / "stubgen_error.pyi"
+    assert stub_file.exists()
+    stub_content = stub_file.read_text()
+    assert (
+        "def identity_capsule(c: types.CapsuleType) -> types.CapsuleType:"
+        in stub_content
+    )
+    # Run mypy on the generated stub file
+    # normal_report -> stdout, error_report -> stderr
+    # Type errors seem to go into normal_report
+    normal_report, error_report, exit_status = api.run([stub_file.as_posix()])
+    print("Normal report:")
+    print(normal_report)
+    print("Error report:")
+    print(error_report)
+    assert exit_status == 1
+    assert 'error: Name "types" is not defined  [name-defined]' in normal_report