This did not get in under the RC, but for completeness I think we should still put it in 2.2

Thanks, got a bit delayed by real life and was also waiting for the other backends to get in first.

A few notes on the implementation:

I moved the common parts to _backend_tk.py, which plays a role similar to backend_qt5.py (but is private because I don't see a good reason to make it public... but perhaps it should? dunno). The patch looks enormous because github's UI doesn't seem to detect the move, possibly because backend_tkagg.py still exists (but is essentially completely new).

I also deprecated FigureManagerTkAgg and NavigationToolbar2TkAgg, both because FigureManagerTk and NavigationToolbar2Tk are available and because I would argue that the former should actually be accessed by third parties as from matplotlib.backends.backend_foo import FigureManager (by the design of backends this will necessarily import the manager class corresponding to the backend); while a similar "single" name is not available for NavigationToolbar2 it could be added as well. However these deprecations are not strictly necessary and can easily be reverted.

AFAICT tkagg does all its rendering to the actual widget in draw() (rather than "buffering" it similarly to how Qt separates draw() from paintEvent()). While it may be interesting to rework this I did not change the design in this PR.

You might want to rebase and re-target v2.2.x directly so that tests aren't borked.

Rebased. Before I retarget this: do you want to later "forwardport" from 2.2 to master?

I expect v2.2.x will be merged up to master at some point (at least until 2.2.0), until it becomes too difficult with all our Python 3 changes. You'll need to rebase again though if you re-target because you'll get all the Python 3 changes in now.

done

needs to be merged into master as well.

This looks like it will cause chaos when a new version is released out of the development version.

If FigureManagerTkAgg NavigationToolbar2TkAgg are meant to disappear, there should be an API change notice.
But I would argue that as long as there is no date/version set for FigureManagerTkAgg NavigationToolbar2TkAgg to disappear they should still be accessible.
And in any case the deprecation messages should include what to use instead of FigureManagerTkAgg NavigationToolbar2TkAgg

@ImportanceOfBeingErnest As far as I can see they are both still there. They are just empty aliases for the General non Agg specific version

@jenshnielsen I wouldn't preclude that you have better eyes than I have, but I don't see them anywhere.
And in any case, doing from matplotlib.backends.backend_tkagg import NavigationToolbar2TkAgg results in an ImportError on current master.

They were deprecated in 2.2 and removed in #10426 (3.0) which is admittedly a shorter cycle than normal, but an API removal notice should be enough.