PEP 735: Add include-project to Deferred Ideas (#4012)

peps/pep-0735.rst

@@ -790,6 +790,38 @@ Compared with changes to ``[project.dependencies]`` and
 Therefore, given that this PEP declines to make changes to the ``[project]``
 table, changing ``[build-system]`` is also deferred.
 
+
+Why not support a Dependency Group which includes the current project?
+----------------------------------------------------------------------
+
+Several usage scenarios for dependency groups revolve around installing a
+dependency group alongside a package defined in the ``[project]`` table.
+For example, testing a package involves installing testing dependencies and the
+package itself. Additionally, the compatibility of a dependency group with the
+main package is a valuable input to lockfile generators.
+
+In such cases, it is desirable for a Dependency Group to declare that it
+depends upon the project itself. Example syntaxes from discussions included
+``{include-project = true}`` and ``{include-group = ":project:"}``.
+
+However, if a specification is established to extend :pep:`508` with Path
+Dependencies, this would result in Dependency Groups having two ways of
+specifying the main package. For example, if ``.`` becomes formally supported,
+and ``{include-project = true}`` is included in this PEP, then dependency
+groups may specify any of the following groups
+
+.. code-block:: toml
+
+    [dependency-groups]
+    case1 = [{include-project = true}]
+    case2 = ["."]
+    case3 = [{include-project = true}, "."]
+    case4 = [{include-project = false}, "."]
+
+In order to avoid a confusing future in which multiple different options
+specify the package defined in ``pyproject.toml``, any syntax for declaring
+this relationship is omitted from this PEP.
+
 .. _prior_art:
 
 Appendix A: Prior Art in Non-Python Languages