=============================
 Documenting Coq with Sphinx
=============================

..
   README.rst is auto-generated from README.template.rst and the coqrst/*.py files
   (in particular coqdomain.py).  Use ``doc/tools/coqrst/regen_readme.py`` to rebuild it.

Coq's reference manual is written in `reStructuredText <http://www.sphinx-doc.org/en/master/usage/restructuredtext/basics.html>`_ (“reST”), and compiled with `Sphinx <http://www.sphinx-doc.org/en/master/>`_.
See `this README <../README.md>`_ for compilation instructions.

In addition to standard reST directives (a directive is similar to a LaTeX environment) and roles (a role is similar to a LaTeX command), the ``coqrst`` plugin loaded by the documentation uses a custom *Coq domain* — a set of Coq-specific directives that define *objects* like tactics, commands (vernacs), warnings, etc. —, some custom *directives*, and a few custom *roles*.  Finally, this manual uses a small DSL to describe tactic invocations and commands.

Coq objects
===========

Our Coq domain define multiple `objects`_.  Each object has a *signature* (think *type signature*), followed by an optional body (a description of that object).  The following example defines two objects: a variant of the ``simpl`` tactic, and an error that it may raise::

   .. tacv:: simpl @pattern at {+ @natural}
      :name: simpl_at

      This applies ``simpl`` only to the :n:`{+ @natural}` occurrences of the subterms
      matching :n:`@pattern` in the current goal.

      .. exn:: Too few occurrences
         :undocumented:

Objects are automatically collected into indices, and can be linked to using the role version of the object's directive. For example, you could link to the tactic variant above using ``:tacv:`simpl_at```, and to its exception using ``:exn:`Too few occurrences```.

Names (link targets) are auto-generated for most simple objects, though they can always be overwritten using a ``:name:`` option, as shown above.

- Options, errors, warnings have their name set to their signature, with ``...`` replacing all notation bits.  For example, the auto-generated name of ``.. exn:: @qualid is not a module`` is ``... is not a module``, and a link to it would take the form ``:exn:`... is not a module```.
- Vernacs (commands) have their name set to the first word of their signature.  For example, the auto-generated name of ``Axiom @ident : @term`` is ``Axiom``, and a link to it would take the form ``:cmd:`Axiom```.
- Vernac variants, tactic notations, and tactic variants do not have a default name.

Most objects should have a body (i.e. a block of indented text following the signature, called “contents” in Sphinx terms).  Undocumented objects should have the ``:undocumented:`` flag instead, as shown above.  When multiple objects have a single description, they can be grouped into a single object, like this (semicolons can be used to separate the names of the objects; names starting with ``_`` will be omitted from the indexes)::

   .. cmdv:: Lemma @ident {* @binder } : @type
             Remark @ident {* @binder } : @type
             Fact @ident {* @binder } : @type
             Corollary @ident {* @binder } : @type
             Proposition @ident {* @binder } : @type
      :name: Lemma; Remark; Fact; Corollary; Proposition

      These commands are all synonyms of :n:`Theorem @ident {* @binder } : type`.

Notations
---------

The signatures of most objects can be written using a succinct DSL for Coq notations (think regular expressions written with a Lispy syntax).  A typical signature might look like ``Hint Extern @natural {? @pattern} => @tactic``, which means that the ``Hint Extern`` command takes a number (``natural``), followed by an optional pattern, and a mandatory tactic.  The language has the following constructs (the full grammar is in `TacticNotations.g </doc/tools/coqrst/notations/TacticNotations.g>`_):

``@…``
  A placeholder (``@ident``, ``@natural``, ``@tactic``\ …)

``{? …}``
  an optional block

``{* …}``, ``{+ …}``
  an optional (``*``) or mandatory (``+``) block that can be repeated, with repetitions separated by spaces

``{*, …}``, ``{+, …}``
  an optional or mandatory repeatable block, with repetitions separated by commas

``{| … | … | … }``
  an alternative, indicating than one of multiple constructs can be used

``%{``, ``%}``, ``%|``
  an escaped character (rendered without the leading ``%``).  In most cases,
  escaping is not necessary.  In particular, the following expressions are
  all parsed as plain text, and do not need escaping: ``{ xyz }``, ``x |- y``.
  But the following escapes *are* needed: ``{| a b %| c | d }``, ``all: %{``.
  (We use ``%`` instead of the usual ``\`` because you'd have to type ``\``
  twice in your reStructuredText file.)

  For more details and corner cases, see `Advanced uses of notations`_ below.

..
   FIXME document the new subscript support

As an exercise, what do the following patterns mean?

.. code::

   pattern {+, @term {? at {+ @natural}}}
   generalize {+, @term at {+ @natural} as @ident}
   fix @ident @natural with {+ (@ident {+ @binder} {? {struct @ident'}} : @type)}

Objects
-------

Here is the list of all objects of the Coq domain (The symbol :black_nib: indicates an object whose signature can be written using the notations DSL):

[OBJECTS]

Coq directives
==============

In addition to the objects above, the ``coqrst`` Sphinx plugin defines the following directives:

[DIRECTIVES]

Coq roles
=========

In addition to the objects and directives above, the ``coqrst`` Sphinx plugin defines the following roles:

[ROLES]

Common mistakes
===============

Improper nesting
----------------

DO
  .. code::

     .. cmd:: Foo @bar

        Foo the first instance of :token:`bar`\ s.

        .. cmdv:: Foo All

           Foo all the :token:`bar`\ s in
           the current context

DON'T
  .. code::

     .. cmd:: Foo @bar

     Foo the first instance of :token:`bar`\ s.

     .. cmdv:: Foo All

     Foo all the :token:`bar`\ s in
     the current context

You can set the ``report_undocumented_coq_objects`` setting in ``conf.py`` to ``"info"`` or ``"warning"`` to get a list of all Coq objects without a description.

Overusing ``:token:``
---------------------

DO
  .. code::

     This is equivalent to :n:`Axiom @ident : @term`.

DON'T
  .. code::

     This is equivalent to ``Axiom`` :token:`ident` : :token:`term`.

..

DO
  .. code::

     :n:`power_tac @term [@ltac]`
       allows :tacn:`ring` and :tacn:`ring_simplify` to recognize …

DON'T
  .. code::

     power_tac :n:`@term` [:n:`@ltac`]
       allows :tacn:`ring` and :tacn:`ring_simplify` to recognize …

..

DO
  .. code::

     :n:`name={*; attr}`

DON'T
  .. code::

     ``name=``:n:`{*; attr}`

Omitting annotations
--------------------

DO
  .. code::

     .. tacv:: assert @form as @simple_intropattern

DON'T
  .. code::

     .. tacv:: assert form as simple_intropattern

Using the ``.. coqtop::`` directive for syntax highlighting
-----------------------------------------------------------

DO
  .. code::

     A tactic of the form:

     .. coqdoc::

        do [ t1 | … | tn ].

     is equivalent to the standard Ltac expression:

     .. coqdoc::

        first [ t1 | … | tn ].

DON'T
  .. code::

     A tactic of the form:

     .. coqtop:: in

        do [ t1 | … | tn ].

     is equivalent to the standard Ltac expression:

     .. coqtop:: in

        first [ t1 | … | tn ].

Overusing plain quotes
----------------------

DO
  .. code::

     The :tacn:`refine` tactic can raise the :exn:`Invalid argument` exception.
     The term :g:`let a = 1 in a a` is ill-typed.

DON'T
  .. code::

     The ``refine`` tactic can raise the ``Invalid argument`` exception.
     The term ``let a = 1 in a a`` is ill-typed.

Plain quotes produce plain text, without highlighting or cross-references.

Overusing the ``example`` directive
-----------------------------------

DO
  .. code::

     Here is a useful axiom:

     .. coqdoc::

        Axiom proof_irrelevance : forall (P : Prop) (x y : P), x=y.

DO
  .. code::

     .. example:: Using proof-irrelevance

        If you assume the axiom above, …

DON'T
  .. code::

     Here is a useful axiom:

     .. example::

        .. coqdoc::

           Axiom proof_irrelevance : forall (P : Prop) (x y : P), x=y.

Tips and tricks
===============

Nested lemmas
-------------

The ``.. coqtop::`` directive does *not* reset Coq after running its contents.  That is, the following will create two nested lemmas (which by default results in a failure)::

   .. coqtop:: all

      Lemma l1: 1 + 1 = 2.

   .. coqtop:: all

      Lemma l2: 2 + 2 <> 1.

Add either ``abort`` to the first block or ``reset`` to the second block to avoid nesting lemmas.

Abbreviations and macros
------------------------

Substitutions for specially-formatted names (like ``|Cic|``, ``|Ltac|`` and ``|Latex|``), along with some useful LaTeX macros, are defined in a `separate file </doc/sphinx/refman-preamble.rst>`_.  This file is automatically included in all manual pages.

Emacs
-----

The ``dev/tools/coqdev.el`` folder contains a convenient Emacs function to quickly insert Sphinx roles and quotes.  It takes a single character (one of ``gntm:```), and inserts one of ``:g:``, ``:n:``, ``:t:``, or an arbitrary role, or double quotes.  You can also select a region of text, and wrap it in single or double backticks using that function.

Use the following snippet to bind it to `F12` in ``rst-mode``::

   (with-eval-after-load 'rst
     (define-key rst-mode-map (kbd "<f12>") #'coqdev-sphinx-rst-coq-action))


Advanced uses of notations
--------------------------


  - Use `%` to escape grammar literal strings that are the same as metasyntax,
    such as ``{``, ``|``, ``}`` and ``{|``.  (While this is optional for
    ``|`` and ``{ ... }`` outside of ``{| ... }``, always using the escape
    requires less thought.)

  - Literals such as ``|-`` and ``||`` don't need to be escaped.

  - The literal ``%`` shouldn't be escaped.

  - Don't use the escape for a ``|`` separator in ``{*`` and ``{+``.  These
    should appear as ``{*|`` and ``{+|``.
