Fix use of --pylab=auto and --matplotlib=auto (#14403)...
Fix use of --pylab=auto and --matplotlib=auto (#14403)
Fixes
#14401 which has been a bug in the 8.22.x and 8.23.x releases.
When I removed the multiple initialisation of Matplotlib backends in
#14330 it broke use of the following:
```bash
ipython --matplotlib
ipython --matplotlib=auto
ipython --pylab
ipython --pylab=auto
```
by failing to display Matplotlib plot. If you specify a particular GUI
event loop such as using
```bash
ipython --pylab=qt
```
then it was and is fine. So for anyone finding this, the workaround
until the next release is to specify a GUI loop rather than relying on
the auto selection.
I didn't notice this as I've been concentrating on moving the Matplotlib
backend logic from IPython to Matplotlib, and with those changes
(matplotlib/matplotlib#27948) the above use cases all work OK.
The fix is to reintroduce the early import of `matplotlib-inline` but
only if both the gui loop is not specified and the Matplotlib version is
before the movement of the backend logic across to it.
There are no explicit tests for this. In the future I will try to think
of some tests for some of this IPython-Matplotlib functionality that
don't involve installing complicated backend dependencies or adding
image comparison tests.
