Add experimental warning to ext-modules in pyproject.toml

Author: abravalheri

setuptools/config/pyprojecttoml.py

@@ -130,6 +130,9 @@ def read_configuration(
     asdict["tool"] = tool_table
     tool_table["setuptools"] = setuptools_table
 
+    if "ext-modules" in setuptools_table:
+        _ExperimentalConfiguration.emit(subject="[tool.setuptools.ext-modules]")
+
     with _ignore_errors(ignore_option_errors):
         # Don't complain about unrelated errors (e.g. tools not using the "tool" table)
         subset = {"project": project_table, "tool": {"setuptools": setuptools_table}}

setuptools/tests/config/test_apply_pyprojecttoml.py

@@ -338,7 +338,8 @@ def test_pyproject_sets_attribute(self, tmp_path, monkeypatch):
         ]
         """
         pyproject.write_text(cleandoc(toml_config), encoding="utf-8")
-        dist = pyprojecttoml.apply_configuration(Distribution({}), pyproject)
+        with pytest.warns(pyprojecttoml._ExperimentalConfiguration):
+            dist = pyprojecttoml.apply_configuration(Distribution({}), pyproject)
         assert len(dist.ext_modules) == 1
         assert dist.ext_modules[0].name == "my.ext"
         assert set(dist.ext_modules[0].sources) == {"hello.c", "world.c"}