Add guide on Poetry

docs/guides/developers.rst

@@ -14,6 +14,7 @@ or customize the documentation appearance.
    reproducible-builds
    embedding-content
    conda
+   poetry
    remove-edit-buttons
    build-using-too-many-resources
    edit-source-links-sphinx

docs/guides/poetry.rst

@@ -0,0 +1,67 @@
+Specifying your dependencies with Poetry
+========================================
+
+Declaring your project metadata
+-------------------------------
+
+Poetry is a :pep:`517`-compliant build backend, which means that
+`it generates your project
+metadata <https://python-poetry.org/docs/pyproject/#poetry-and-pep-517>`_
+using a standardized interface that can be consumed directly by pip.
+Therefore, by making sure that
+the ``build-system`` section of your ``pyproject.toml``
+declares the build backend as follows:
+
+.. code-block:: toml
+   :caption: pyproject.toml
+
+   [build-system]
+   requires = ["poetry_core>=1.0.0"]
+   build-backend = "poetry.core.masonry.api"
+
+You will be able to install it on Read the Docs just using pip,
+using a configuration like this:
+
+.. code-block:: yaml
+   :caption: .readthedocs.yaml
+   :emphasize-lines: 8-11
+
+   version: 2
+
+   build:
+     os: ubuntu-20.04
+     tools:
+       python: "3.9"
+
+   python:
+     install:
+       - method: pip
+         path: .
+
+For example, the `rich <https://rich.readthedocs.io/>`_ Python library
+`uses Poetry <https://github.com/willmcgugan/rich/blob/ba5d0c2c/pyproject.toml#L49-L51>`_
+to declare its library dependencies
+and installs itself on Read the Docs
+`with pip <https://github.com/willmcgugan/rich/blob/ba5d0c2c/.readthedocs.yml#L18-L19>`_.
+
+Locking your dependencies
+-------------------------
+
+With you ``pyproject.toml`` file you are free to `specify the dependency
+versions <https://python-poetry.org/docs/dependency-specification/>`_
+that are more appropriate for your project,
+either by leaving them unpinned or setting some constraints.
+However, to achieve :doc:`/guides/reproducible-builds`
+it is better that you lock your dependencies,
+so that the decision to upgrade any of them is yours.
+Poetry does this using ``poetry.lock`` files
+that contain the exact versions of all your transitive dependencies
+(that is, all the dependencies of your dependencies).
+
+The first time you run ``poetry install`` in your project directory
+`Poetry will generate a new poetry.lock
+file <https://python-poetry.org/docs/basic-usage/#installing-without-poetrylock>`_
+with the versions available at that moment.
+You can then `commit your poetry.lock to version
+control <https://python-poetry.org/docs/basic-usage/#commit-your-poetrylock-file-to-version-control>`_
+so that Read the Docs also uses these exact dependencies.