Allow the jinja2 environment class to be overridden.

[smurfix]

I need this change because I have to override a couple of Jinja2's templating functions.

Better than monkeypatching flask.app.Environment. ;-)

[danielchatfield]

If I recall correctly, pretty much this exact thing got rejected and the response was that you should subclass Flask to change that. I'll see if I can find it.

[danielchatfield]

I can't find the exact issue in the couple of minutes I spent looking but the recommended way of doing this is to create a subclass of Flask and change the jinja_env method. May I ask why you are overriding jinja2s templating functions?

[smurfix]

OK, I did it that way, no problem.

What I'm trying to do is to get jinja2 to accept and (ideally) debug my templates. I'm loading them from a database, and there's no reason why I couldn't store the compiled code alongside the source.

However I haven't made any inroads into providing meaningful backtraces yet, when the template's "filename" is really the database index.

[char101]

How do I override create_jinja_environment without having to copy paste the implementation or monkey patching the environment object?

I think providing overridable flask environment class will result in much cleaner code than current alternatives.

[untitaker]

Instead of introducing another attribute to the Flask object i'd suggest we add an optional environment_cls param to create_jinja_environment. Subclasses of Flask can then override the method with one that calls the parent method with this param.

[ThiefMaster]

That sounds pretty ugly... and it will break if, for whatever reason, a future version adds another argument which is passed by flask when calling the method.

I'd prefer the class attribute.

[untitaker]

I only considered it because there are IMO already far too many attributes on the Flask object, many of them just being shortcuts of something else.

[untitaker]

Apparently this has been duplicated by #1422. I've merged that PR since it also had a testcase. I liked your naming style more though, so I've also renamed the class.

Thanks!