templateing: jinja2: pass kwargs for environment

[blueyed]

I think it would be good to pass something like env_kwargs via https://github.com/blueyed/starlette/blob/24c135de71ac56a73f7f797258115941579155bf/starlette/templating.py#L51-L53.

While you can change the env afterwards, it would allow Jinja2 to validate e.g. enable_async, and call load_extensions etc.

[lovelydinosaur]

Yup I'm up for this. We'll want to autoescape and loader be overridable there too.

Related to this is configuring env.globals.

We could just use **options, and support both globals and any valid Environment keyword arguments?

[blueyed]

I think it should just allow more easily to set the env altogether.

url_for could be still set to the globals then by default.

But it is also the only reason for requiring request to be in the context (ValueError('context must include a "request" key')), and if url_for is not used in a template, it is not used (by default). I.e. it might be better to raise the error then from url_for only.

Not sure about backward compatibility with regard to removing directory from the constructor, but #473 might indicate that it is not used much (at least with tested code).. ;)

I am using a quite customized version already myself, and that is fine, but wanted to provide this feedback anyway.

[liquiddandruff]

+1 as well, since as currently stands it's not possible to change common fields such as auto_reload, enable_async when loading the environment, especially when deploying through a docker environment.