Update "install_requires vs. requirements files" discussion

source/discussions/install-requires-vs-requirements.rst

@@ -1,89 +1,90 @@
-.. _`install_requires vs requirements files`:
+==========================================
+Package dependencies vs requirements files
+==========================================
 
-======================================
-install_requires vs requirements files
-======================================
 
+Package dependencies
+====================
 
-install_requires
-----------------
+Packages can declare dependencies, i.e., other packages that they need
+to function. The standard method to do so is to set the
+:ref:`dependencies key <writing-pyproject-toml-dependencies>` in the
+``[project]`` section of a ``pyproject.toml`` file. When installing a
+package, installers like :ref:`pip` will automatically install the
+dependencies.  This should be used for packages that the project
+**minimally** needs to run correctly.
 
-``install_requires`` is a :ref:`setuptools` :file:`setup.py` keyword that
-should be used to specify what a project **minimally** needs to run correctly.
-When the project is installed by :ref:`pip`, this is the specification that is
-used to install its dependencies.
-
-For example, if the project requires A and B, your ``install_requires`` would be
+For example, if the project requires A and B, your ``dependencies`` would be
 like so:
 
-::
+.. code-block:: toml
 
- install_requires=[
-    'A',
-    'B'
- ]
+   [project]
+   dependencies = ["A", "B"]
 
 Additionally, it's best practice to indicate any known lower or upper bounds.
 
 For example, it may be known, that your project requires at least v1 of 'A', and
 v2 of 'B', so it would be like so:
 
-::
+.. code-block:: toml
 
- install_requires=[
-    'A>=1',
-    'B>=2'
- ]
+   [project]
+   dependencies = [
+     "A>=1",
+     "B>=2"
+   ]
 
 It may also be known that project 'A' introduced a change in its v2
 that breaks the compatibility of your project with v2 of 'A' and later,
 so it makes sense to not allow v2:
 
-::
+.. code-block:: toml
 
- install_requires=[
-    'A>=1,<2',
-    'B>=2'
- ]
+   [project]
+   dependencies = [
+     "A>=1,<2",
+     "B>=2"
+    ]
 
-It is not considered best practice to use ``install_requires`` to pin
-dependencies to specific versions, or to specify sub-dependencies
+It is not considered best practice to use ``dependencies`` to pin
+dependencies to specific versions, or to specify transitive dependencies
 (i.e. dependencies of your dependencies).  This is overly-restrictive, and
 prevents the user from gaining the benefit of dependency upgrades.
 
-Lastly, it's important to understand that ``install_requires`` is a listing of
-"Abstract" requirements, i.e just names and version restrictions that don't
-determine where the dependencies will be fulfilled from (i.e. from what
-index or source).  The where (i.e. how they are to be made "Concrete") is to
-be determined at install time using :ref:`pip` options. [1]_
+Lastly, it's important to understand that ``dependencies`` is a listing of
+"abstract" requirements, i.e., just names and version restrictions, but doesn't
+determine where the dependencies will be fulfilled from (from what package
+index or source).  The where (i.e. how they are to be made "concrete") is to
+be determined at install time, e.g., using :ref:`pip` options. [1]_
 
 
 Requirements files
-------------------
+==================
 
-:ref:`Requirements Files <pip:Requirements Files>` described most simply, are
+:ref:`Requirements Files <pip:Requirements Files>`, described most simply, are
 just a list of :ref:`pip:pip install` arguments placed into a file.
 
-Whereas ``install_requires`` defines the dependencies for a single project,
+Whereas ``dependencies`` defines the dependencies for a single project,
 :ref:`Requirements Files <pip:Requirements Files>` are often used to define
 the requirements for a complete Python environment.
 
-Whereas ``install_requires`` requirements are minimal, requirements files
+Whereas ``dependencies`` requirements are minimal, requirements files
 often contain an exhaustive listing of pinned versions for the purpose of
 achieving :ref:`repeatable installations <pip:Repeatability>` of a complete
 environment.
 
-Whereas ``install_requires`` requirements are "Abstract", i.e. not associated
+Whereas ``dependencies`` requirements are "abstract", i.e., not associated
 with any particular index, requirements files often contain pip
 options like ``--index-url`` or ``--find-links`` to make requirements
-"Concrete", i.e. associated with a particular index or directory of
+"concrete", i.e., associated with a particular index or directory of
 packages. [1]_
 
-Whereas ``install_requires`` metadata is automatically analyzed by pip during an
+Whereas ``dependencies`` metadata is automatically analyzed by pip during an
 install, requirements files are not, and only are used when a user specifically
 installs them using ``python -m pip install -r``.
 
 ----
 
-.. [1] For more on "Abstract" vs "Concrete" requirements, see
+.. [1] For more on "abstract" vs "concrete" requirements, see
        https://caremad.io/posts/2013/07/setup-vs-requirement/.

source/guides/distributing-packages-using-setuptools.rst

@@ -394,8 +394,6 @@ package, set ``py_modules`` to a list of the names of the modules (minus the
 minimally needs to run. When the project is installed by :ref:`pip`, this is the
 specification that is used to install its dependencies.
 
-For more on using "install_requires" see :ref:`install_requires vs Requirements files`.
-
 
 .. _python_requires:
 

source/guides/writing-pyproject-toml.rst

@@ -154,6 +154,8 @@ This field is required, although it is often marked as dynamic using
 Dependencies and requirements
 =============================
 
+.. _writing-pyproject-toml-dependencies:
+
 ``dependencies``/``optional-dependencies``
 ------------------------------------------