Plugin hook for adding extra template context variables

[simonw]

It turns out I need this for simonw/datasette-auth-github#5

It can be modelled on the extra_body_script hook: https://datasette.readthedocs.io/en/stable/plugins.html#extra-body-script-template-database-table-view-name-datasette

[simonw]

Example usage:

@hookimpl
def extra_template_vars(request):
    return {
        "auth": request.scope.get("auth"),
    }

[simonw]

It should allow for awaitables too, to allow for execution of SQL. For example:

@hookimpl
def extra_template_vars(datasette):
    async def inner():
        first_db = list(datasette.databases.keys())[0]
        return {
            "sqlite_version": (
                await datasette.execute(first_db, "select sqlite_version()")
            ).rows[0][0]
        }
    return inner