"""Marking the views whose answers — including their failures — are JSON.

STD-09. Deciding "JSON or HTML page" from the URL path could not work here,
and the audit's own recommendation ("gestion d'erreurs API par préfixe d'URL
codé en dur", fix the prefixes) would not have fixed it either. Three of the
sixteen JSON views sit at paths no prefix can single out:

    /matches/<int:match_id>/toggle-presence/<int:participant_id>
    /team-matches/<int:match_id>/toggle-presence/<int:participant_id>
    /teams/<int:team_id>/toggle_status/<int:player_id>

They are interleaved with the HTML routes of the same blueprints, and the
templates fetch them. Any prefix wide enough to catch them catches every
page of the section with them.

So the view says so itself. `wants_json_response()` in app.py reads the mark
off the registered view function, and `tests/test_api_error_format.py` walks
the URL map to prove that every view calling `jsonify` carries it — the
mechanism that was missing before was not a better list, it was anything at
all that checked the list.

Usage — directly under the route decorator, above `login_required`, so the
mark lands on the object the route registers::

    @matches_bp.route('/api/events')
    @json_endpoint
    @login_required
    def api_events():
        ...
"""


def json_endpoint(view):
    """Mark a view as answering in JSON, errors included.

    Args:
        view: The view function, already wrapped by any decorator below this
            one (`login_required` in every current case).

    Returns:
        The same object, with the mark set. Nothing is wrapped: an extra
        wrapper here would be one more thing between Flask and the view for
        no gain, and `functools.wraps` copying `__dict__` is exactly the
        detail that would make this fragile.
    """
    view.returns_json = True
    return view