Add docs about ext-modules in pyproject.toml

docs/userguide/ext_modules.rst

@@ -27,22 +27,41 @@ and all project metadata configuration in the ``pyproject.toml`` file:
    version = "0.42"
 
 To instruct setuptools to compile the ``foo.c`` file into the extension module
-``mylib.foo``, we need to add a ``setup.py`` file similar to the following:
+``mylib.foo``, we need to define an appropriate configuration in either
+``pyproject.toml`` [#pyproject.toml]_ or ``setup.py`` file ,
+similar to the following:
 
-.. code-block:: python
+.. tab:: pyproject.toml
 
-   from setuptools import Extension, setup
+    .. code-block:: toml
 
-   setup(
-       ext_modules=[
-           Extension(
-               name="mylib.foo",  # as it would be imported
-                                  # may include packages/namespaces separated by `.`
-
-               sources=["foo.c"], # all sources are compiled into a single binary file
-           ),
+       [tool.setuptools]
+       ext-modules = [
+         {name = "mylib.foo", sources = ["foo.c"]}
        ]
-   )
+
+.. tab:: setup.py
+
+    .. code-block:: python
+
+       from setuptools import Extension, setup
+
+       setup(
+           ext_modules=[
+               Extension(
+                   name="mylib.foo",
+                   sources=["foo.c"],
+               ),
+           ]
+       )
+
+The ``name`` value corresponds to how the extension module would be
+imported and may include packages/namespaces separated by ``.``.
+The ``sources`` value is a list of all source files that are compiled
+into a single binary file.
+Optionally any other parameter of :class:`setuptools.Extension` can be defined
+in the configuration file (but in the case of ``pyproject.toml`` they must be
+written using :wiki:`kebab-case` convention).
 
 .. seealso::
    You can find more information on the `Python docs about C/C++ extensions`_.
@@ -168,6 +187,16 @@ Extension API Reference
 .. autoclass:: setuptools.Extension
 
 
+----
+
+.. rubric:: Notes
+
+.. [#pyproject.toml]
+   Declarative configuration of extension modules via ``pyproject.toml`` was
+   introduced recently and is still considered experimental.
+   Therefore it might change in future versions of ``setuptools``.
+
+
 .. _Python docs about C/C++ extensions: https://docs.python.org/3/extending/extending.html
 .. _Cython: https://cython.readthedocs.io/en/stable/index.html
 .. _directory options: https://gcc.gnu.org/onlinedocs/gcc/Directory-Options.html

docs/userguide/pyproject_config.rst

@@ -88,6 +88,9 @@ file, and can be set via the ``tool.setuptools`` table:
 Key                       Value Type (TOML)           Notes
 ========================= =========================== =========================
 ``py-modules``            array                       See tip below.
+``ext-modules``           array of                    **Experimental** - Each item corresponds to a
+                          tables/inline-tables        :class:`setuptools.Extension` object and may define
+                                                      the associated parameters in :wiki:`kebab-case`.
 ``packages``              array or ``find`` directive See tip below.
 ``package-dir``           table/inline-table          Used when explicitly/manually listing ``packages``.
 ------------------------- --------------------------- -------------------------

setuptools/extension.py

@@ -127,7 +127,7 @@ class Extension(_Extension):
     :keyword bool py_limited_api:
       opt-in flag for the usage of :doc:`Python's limited API <python:c-api/stable>`.
 
-    :raises setuptools.errors.PlatformError: if 'runtime_library_dirs' is
+    :raises setuptools.errors.PlatformError: if ``runtime_library_dirs`` is
       specified on Windows. (since v63)
     """