Developing a « TODO » extension

The objective of this tutorial is to create a more comprehensive extension than that created in Développement d’une extension « Hello world ». Whereas that guide just covered writing a custom directive, this guide adds multiple directives, along with custom nodes, additional config values and custom event handlers. To this end, we will cover a todo extension that adds capabilities to include todo entries in the documentation, and to collect these in a central place. This is similar the sphinxext.todo extension distributed with Sphinx.

Résumé

Note

To understand the design of this extension, refer to Important objects and Build Phases.

Nous voulons que l’extension ajoute les éléments suivants à Sphinx :

  • A todo directive, containing some content that is marked with « TODO » and only shown in the output if a new config value is set. Todo entries should not be in the output by default.

  • A todolist directive that creates a list of all todo entries throughout the documentation.

Pour cela, nous devrons ajouter les éléments suivants à Sphinx :

  • Nouvelles directives, appelées `` todo`` et `` todolist``.

  • Nouveaux noeuds d’arborescence de documents représentant ces directives, généralement appelés aussi `` todo`` et `` todolist``. Nous n’aurions pas besoin de nouveaux nœuds si les nouvelles directives ne produisaient qu’un contenu représentable par les nœuds existants.

  • Une nouvelle valeur de configuration `` todo_include_todos`` (les noms de valeurs de configuration doivent commencer par le nom de l’extension, afin de rester uniques), qui contrôle si les entrées à faire sont intégrées à la sortie.

  • New event handlers: one for the doctree-resolved event, to replace the todo and todolist nodes, one for env-merge-info to merge intermediate results from parallel builds, and one for env-purge-doc (the reason for that will be covered later).

Pré-requis

As with Développement d’une extension « Hello world », we will not be distributing this plugin via PyPI so once again we need a Sphinx project to call this from. You can use an existing project or create a new one using sphinx-quickstart.

We assume you are using separate source (source) and build (build) folders. Your extension file could be in any folder of your project. In our case, let’s do the following:

  1. Create an _ext folder in source

  2. Create a new Python file in the _ext folder called todo.py

Voici un exemple d’arborescence que vous pourriez obtenir :

└── source
    ├── _ext
    │   └── todo.py
    ├── _static
    ├── conf.py
    ├── somefolder
    ├── index.rst
    ├── somefile.rst
    └── someotherfile.rst

Écriture de l’extension

Open todo.py and paste the following code in it, all of which we will explain in detail shortly:

  1from docutils import nodes
  2from docutils.parsers.rst import Directive
  3
  4from sphinx.application import Sphinx
  5from sphinx.locale import _
  6from sphinx.util.docutils import SphinxDirective
  7from sphinx.util.typing import ExtensionMetadata
  8
  9
 10class todo(nodes.Admonition, nodes.Element):
 11    pass
 12
 13
 14class todolist(nodes.General, nodes.Element):
 15    pass
 16
 17
 18def visit_todo_node(self, node):
 19    self.visit_admonition(node)
 20
 21
 22def depart_todo_node(self, node):
 23    self.depart_admonition(node)
 24
 25
 26class TodolistDirective(Directive):
 27    def run(self):
 28        return [todolist('')]
 29
 30
 31class TodoDirective(SphinxDirective):
 32    # this enables content in the directive
 33    has_content = True
 34
 35    def run(self):
 36        targetid = 'todo-%d' % self.env.new_serialno('todo')
 37        targetnode = nodes.target('', '', ids=[targetid])
 38
 39        todo_node = todo('\n'.join(self.content))
 40        todo_node += nodes.title(_('Todo'), _('Todo'))
 41        self.state.nested_parse(self.content, self.content_offset, todo_node)
 42
 43        if not hasattr(self.env, 'todo_all_todos'):
 44            self.env.todo_all_todos = []
 45
 46        self.env.todo_all_todos.append({
 47            'docname': self.env.docname,
 48            'lineno': self.lineno,
 49            'todo': todo_node.deepcopy(),
 50            'target': targetnode,
 51        })
 52
 53        return [targetnode, todo_node]
 54
 55
 56def purge_todos(app, env, docname):
 57    if not hasattr(env, 'todo_all_todos'):
 58        return
 59
 60    env.todo_all_todos = [todo for todo in env.todo_all_todos if todo['docname'] != docname]
 61
 62
 63def merge_todos(app, env, docnames, other):
 64    if not hasattr(env, 'todo_all_todos'):
 65        env.todo_all_todos = []
 66    if hasattr(other, 'todo_all_todos'):
 67        env.todo_all_todos.extend(other.todo_all_todos)
 68
 69
 70def process_todo_nodes(app, doctree, fromdocname):
 71    if not app.config.todo_include_todos:
 72        for node in doctree.findall(todo):
 73            node.parent.remove(node)
 74
 75    # Replace all todolist nodes with a list of the collected todos.
 76    # Augment each todo with a backlink to the original location.
 77    env = app.builder.env
 78
 79    if not hasattr(env, 'todo_all_todos'):
 80        env.todo_all_todos = []
 81
 82    for node in doctree.findall(todolist):
 83        if not app.config.todo_include_todos:
 84            node.replace_self([])
 85            continue
 86
 87        content = []
 88
 89        for todo_info in env.todo_all_todos:
 90            para = nodes.paragraph()
 91            filename = env.doc2path(todo_info['docname'], base=None)
 92            description = _(
 93                '(The original entry is located in %s, line %d and can be found '
 94            ) % (filename, todo_info['lineno'])
 95            para += nodes.Text(description)
 96
 97            # Create a reference
 98            newnode = nodes.reference('', '')
 99            innernode = nodes.emphasis(_('here'), _('here'))
100            newnode['refdocname'] = todo_info['docname']
101            newnode['refuri'] = app.builder.get_relative_uri(fromdocname, todo_info['docname'])
102            newnode['refuri'] += '#' + todo_info['target']['refid']
103            newnode.append(innernode)
104            para += newnode
105            para += nodes.Text('.)')
106
107            # Insert into the todolist
108            content.extend((
109                todo_info['todo'],
110                para,
111            ))
112
113        node.replace_self(content)
114
115
116def setup(app: Sphinx) -> ExtensionMetadata:
117    app.add_config_value('todo_include_todos', False, 'html')
118
119    app.add_node(todolist)
120    app.add_node(
121        todo,
122        html=(visit_todo_node, depart_todo_node),
123        latex=(visit_todo_node, depart_todo_node),
124        text=(visit_todo_node, depart_todo_node),
125    )
126
127    app.add_directive('todo', TodoDirective)
128    app.add_directive('todolist', TodolistDirective)
129    app.connect('doctree-resolved', process_todo_nodes)
130    app.connect('env-purge-doc', purge_todos)
131    app.connect('env-merge-info', merge_todos)
132
133    return {
134        'version': '0.1',
135        'parallel_read_safe': True,
136        'parallel_write_safe': True,
137    }

This is far more extensive extension than the one detailed in Développement d’une extension « Hello world », however, we will will look at each piece step-by-step to explain what’s happening.

The node classes

Let’s start with the node classes:

 1
 2
 3class todo(nodes.Admonition, nodes.Element):
 4    pass
 5
 6
 7class todolist(nodes.General, nodes.Element):
 8    pass
 9
10
11def visit_todo_node(self, node):
12    self.visit_admonition(node)
13
14

Les classes de noeuds n’ont généralement rien à faire à part hériter des classes docutils standard définies dans: mod: docutils.nodes. todo hérite de Admonition, car il devrait être traité comme une note ou un avertissement, todolist n’est qu’un nœud « général ».

Note

Many extensions will not have to create their own node classes and work fine with the nodes already provided by docutils and Sphinx.

Attention

It is important to know that while you can extend Sphinx without leaving your conf.py, if you declare an inherited node right there, you’ll hit an unobvious PickleError. So if something goes wrong, please make sure that you put inherited nodes into a separate Python module.

For more details, see:

The directive classes

A directive class is a class deriving usually from docutils.parsers.rst.Directive. The directive interface is also covered in detail in the docutils documentation; the important thing is that the class should have attributes that configure the allowed markup, and a run method that returns a list of nodes.

Looking first at the TodolistDirective directive:

1
2
3class TodolistDirective(Directive):
4    def run(self):

It’s very simple, creating and returning an instance of our todolist node class. The TodolistDirective directive itself has neither content nor arguments that need to be handled. That brings us to the TodoDirective directive:

 1
 2class TodoDirective(SphinxDirective):
 3    # this enables content in the directive
 4    has_content = True
 5
 6    def run(self):
 7        targetid = 'todo-%d' % self.env.new_serialno('todo')
 8        targetnode = nodes.target('', '', ids=[targetid])
 9
10        todo_node = todo('\n'.join(self.content))
11        todo_node += nodes.title(_('Todo'), _('Todo'))
12        self.state.nested_parse(self.content, self.content_offset, todo_node)
13
14        if not hasattr(self.env, 'todo_all_todos'):
15            self.env.todo_all_todos = []
16
17        self.env.todo_all_todos.append({
18            'docname': self.env.docname,
19            'lineno': self.lineno,
20            'todo': todo_node.deepcopy(),
21            'target': targetnode,
22        })
23
24        return [targetnode, todo_node]

Several important things are covered here. First, as you can see, we’re now subclassing the SphinxDirective helper class instead of the usual Directive class. This gives us access to the build environment instance using the self.env property. Without this, we’d have to use the rather convoluted self.state.document.settings.env. Then, to act as a link target (from TodolistDirective), the TodoDirective directive needs to return a target node in addition to the todo node. The target ID (in HTML, this will be the anchor name) is generated by using env.new_serialno which returns a new unique integer on each call and therefore leads to unique target names. The target node is instantiated without any text (the first two arguments).

On creating admonition node, the content body of the directive are parsed using self.state.nested_parse. The first argument gives the content body, and the second one gives content offset. The third argument gives the parent node of parsed result, in our case the todo node. Following this, the todo node is added to the environment. This is needed to be able to create a list of all todo entries throughout the documentation, in the place where the author puts a todolist directive. For this case, the environment attribute todo_all_todos is used (again, the name should be unique, so it is prefixed by the extension name). It does not exist when a new environment is created, so the directive must check and create it if necessary. Various information about the todo entry’s location are stored along with a copy of the node.

Dans la dernière ligne, les nœuds qui doivent être mis dans le doctree sont retournés : le nœud cible et le nœud d’admonition.

La structure de noeud renvoyée par la directive ressemble à ceci

+--------------------+
| target node        |
+--------------------+
+--------------------+
| todo node          |
+--------------------+
  \__+--------------------+
     | admonition title   |
     +--------------------+
     | paragraph          |
     +--------------------+
     | ...                |
     +--------------------+

The event handlers

Event handlers are one of Sphinx’s most powerful features, providing a way to do hook into any part of the documentation process. There are many events provided by Sphinx itself, as detailed in the API guide, and we’re going to use a subset of them here.

Let’s look at the event handlers used in the above example. First, the one for the env-purge-doc event:

1def purge_todos(app, env, docname):
2    if not hasattr(env, 'todo_all_todos'):
3        return
4
5    env.todo_all_todos = [todo for todo in env.todo_all_todos if todo['docname'] != docname]
6

Étant donné que nous stockons des informations à partir de fichiers source dans l’environnement, qui est persistant, il peut devenir obsolète lorsque le fichier source est modifié. Par conséquent, avant que chaque fichier source ne soit lu, les enregistrements de celui-ci sont effacés et l’événement :event: env-purge-doc donne aux extensions la possibilité de faire de même. Nous effaçons ici tous les tâches dont le nom correspond à celui de la liste todo_all_todos. S’il reste des tâches dans le document, elles seront ajoutées à nouveau lors de l’analyse.

The next handler, for the env-merge-info event, is used during parallel builds. As during parallel builds all threads have their own env, there’s multiple todo_all_todos lists that need to be merged:

1    if not hasattr(env, 'todo_all_todos'):
2        env.todo_all_todos = []
3    if hasattr(other, 'todo_all_todos'):
4        env.todo_all_todos.extend(other.todo_all_todos)
5

The other handler belongs to the doctree-resolved event:

 1    if not app.config.todo_include_todos:
 2        for node in doctree.findall(todo):
 3            node.parent.remove(node)
 4
 5    # Replace all todolist nodes with a list of the collected todos.
 6    # Augment each todo with a backlink to the original location.
 7    env = app.builder.env
 8
 9    if not hasattr(env, 'todo_all_todos'):
10        env.todo_all_todos = []
11
12    for node in doctree.findall(todolist):
13        if not app.config.todo_include_todos:
14            node.replace_self([])
15            continue
16
17        content = []
18
19        for todo_info in env.todo_all_todos:
20            para = nodes.paragraph()
21            filename = env.doc2path(todo_info['docname'], base=None)
22            description = _(
23                '(The original entry is located in %s, line %d and can be found '
24            ) % (filename, todo_info['lineno'])
25            para += nodes.Text(description)
26
27            # Create a reference
28            newnode = nodes.reference('', '')
29            innernode = nodes.emphasis(_('here'), _('here'))
30            newnode['refdocname'] = todo_info['docname']
31            newnode['refuri'] = app.builder.get_relative_uri(fromdocname, todo_info['docname'])
32            newnode['refuri'] += '#' + todo_info['target']['refid']
33            newnode.append(innernode)
34            para += newnode
35            para += nodes.Text('.)')
36
37            # Insert into the todolist
38            content.extend((
39                todo_info['todo'],
40                para,
41            ))
42
43        node.replace_self(content)

The doctree-resolved event is emitted at the end of phase 3 (resolving) and allows custom resolving to be done. The handler we have written for this event is a bit more involved. If the todo_include_todos config value (which we’ll describe shortly) is false, all todo and todolist nodes are removed from the documents. If not, todo nodes just stay where and how they are. todolist nodes are replaced by a list of todo entries, complete with backlinks to the location where they come from. The list items are composed of the nodes from the todo entry and docutils nodes created on the fly: a paragraph for each entry, containing text that gives the location, and a link (reference node containing an italic node) with the backreference. The reference URI is built by sphinx.builders.Builder.get_relative_uri() which creates a suitable URI depending on the used builder, and appending the todo node’s (the target’s) ID as the anchor name.

The setup function

As noted previously, the setup function is a requirement and is used to plug directives into Sphinx. However, we also use it to hook up the other parts of our extension. Let’s look at our setup function:

 1def setup(app: Sphinx) -> ExtensionMetadata:
 2    app.add_config_value('todo_include_todos', False, 'html')
 3
 4    app.add_node(todolist)
 5    app.add_node(
 6        todo,
 7        html=(visit_todo_node, depart_todo_node),
 8        latex=(visit_todo_node, depart_todo_node),
 9        text=(visit_todo_node, depart_todo_node),
10    )
11
12    app.add_directive('todo', TodoDirective)
13    app.add_directive('todolist', TodolistDirective)
14    app.connect('doctree-resolved', process_todo_nodes)
15    app.connect('env-purge-doc', purge_todos)
16    app.connect('env-merge-info', merge_todos)
17
18    return {
19        'version': '0.1',
20        'parallel_read_safe': True,
21        'parallel_write_safe': True,
22    }

The calls in this function refer to the classes and functions we added earlier. What the individual calls do is the following:

  • : meth: ~ Sphinx.add_config_value indique à Sphinx qu’il doit reconnaître la nouvelle valeur config todo_include_todos, dont la valeur par défaut doit être False (ceci indique également à Sphinx qu’il s’agit d’une valeur booléenne) .

    If the third argument was 'html', HTML documents would be full rebuild if the config value changed its value. This is needed for config values that influence reading (build phase 1 (reading)).

  • add_node() adds a new node class to the build system. It also can specify visitor functions for each supported output format. These visitor functions are needed when the new nodes stay until phase 4 (writing). Since the todolist node is always replaced in phase 3 (resolving), it doesn’t need any.

  • add_directive() adds a new directive, given by name and class.

  • Enfin, meth: ~ Sphinx.connect ajoute un gestionnaire d’événements à l’événement dont le nom est donné par le premier argument. La fonction de gestionnaire d’événement est appelée avec plusieurs arguments qui sont documentés avec l’événement.

With this, our extension is complete.

Using the extension

As before, we need to enable the extension by declaring it in our conf.py file. There are two steps necessary here:

  1. Add the _ext directory to the Python path using sys.path.append. This should be placed at the top of the file.

  2. Update or create the extensions list and add the extension file name to the list

In addition, we may wish to set the todo_include_todos config value. As noted above, this defaults to False but we can set it explicitly.

Par exemple :

import os
import sys

sys.path.append(os.path.abspath("./_ext"))

extensions = ['todo']

todo_include_todos = False

You can now use the extension throughout your project. For example:

index.rst
Hello, world
============

.. toctree::
   somefile.rst
   someotherfile.rst

Hello world. Below is the list of TODOs.

.. todolist::
somefile.rst
foo
===

Some intro text here...

.. todo:: Fix this
someotherfile.rst
bar
===

Some more text here...

.. todo:: Fix that

Because we have configured todo_include_todos to False, we won’t actually see anything rendered for the todo and todolist directives. However, if we toggle this to true, we will see the output described previously.

Lectures complémentaires

For more information, refer to the docutils documentation and Sphinx Extensions API.