A better way to store extension data on the environment

[timhoffm]

Problem

The approach to storing extension data is explained only vaguely.

From the env-merge-info description and
the todo extension tutorial I infer that one has to add arbitrary attributes to the env object.

This doesn't look very clean. It risks breaking the object and one has to be careful that the data is already added (lots of hasattr() checks).

Proposal

• Add a dict env.extension_data and recommend extensions writing there.
• Can one initialize the extension data instead of checking in various places if it exists? Would env-before-read-docs the right place? I.e.

def setup(app):
    ...
    app.connect("env-before-read-docs", setup_data)

def setup_data(app, env, docnames):
    env.extension_data['todo_all_todos'] = []

[tk0miya]

Absolutely. Adding arbitrary attributes to the env object is ugly. Actually, the real "todo" extension uses a Domain component as a datastore. It can define methods for initialization, gathering contents, merging, and purging. To support parallel build, extension should support both merging and purging. So the Domain component is better to implement it, I think