Simplify JobContext

[onlyann]

The JobContext class mixes fields that are intended to be used by consumers of this library while other fields are used internally. 

As part of v3, it is a good time to clean up JobContext and only expose the fields that are intended for public use.
There is also the opportunity to simplify typing by removing the task field.

[medihack]

Closed by #1213

[ewjoachim]

(as seen in #1257 (comment), maybe the task was useful after all...)

[onlyann]

(as seen in #1257 (comment), maybe the task was useful after all...)

Rather than reintroducing a circular reference with the task, how about adding useful fields directly on JobContext, such as the retry strategy instance in this case?

[ewjoachim]

I think it was pretty useful to have the task there in the end. Is there really no simple way we can make it work for typing ?

[onlyann]

Sorry, I don't have a better suggestion.

[medihack]

Then let's re-add the task to the JobContext and have a beta v3 release (it's the last issue left in v3 milestone). @onlyann, do you want to re-add it, or should I?

[onlyann]

Happy for you to add it @medihack.

Looking back at the codebase, the JobContext has the task_name and the app which is enough to look up the task without passing it in.

Effectively, I think you can simply add a new property/method that returns:

self.app.tasks.get(self.job.task_name)

[medihack]

Good point. Then, I don't see a need to do anything (maybe add a hint to the documentation on how to get the task) and keep the API simple. @ewjoachim Ok for you, too?

[ewjoachim]

Ok !

[medihack]

Cool. I will add a small hint about retrieving the task with its parameters to the documentation under the "Get more context for task execution" section and then close the issue.