I guess this needs a test....

OK, So I'm not sure about this. This is only triggered by

import numpy as np
import matplotlib.pyplot as plt

x = np.arange(10.0)
np.random.seed(1024)
mat = np.random.randn(10, 10)
plt.contour(x, x, mat)

# for a solid colorbar:
cbar = plt.colorbar(location='bottom')
cbar.filled = True
cbar.draw_all()
plt.show()

Note that setting filled=True above turns the colorbar solid. However, this is pretty non-standard API, and a pretty strange way to display contours. The user has to manually call draw_all to get this to even happen at all.

So I'll suggest this should be merged to cover this strange edge case, but I'm not particularly convinced we want to protect this behaviour with a test.

If you do plt.colorbar(filler=True) instead, you get:

issue18595.py:12: MatplotlibDeprecationWarning: The 'filled' parameter to Colorbar has no effect because it is overridden by the mappable; it is deprecated since 3.3 and will be removed two minor releases later.
  cbar = plt.colorbar(filled=True)

so I'm convinced that filled probably should have been deprecated as an accessible attribute.

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

$ git checkout v3.3.x
$ git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

$ git cherry-pick -m1 d17905cf70600ef3a0123bc869bd9e06b54017de

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

$ git commit -am 'Backport PR #18860: FIX: stop deprecation message colorbar'

4. Push to a named branch :

git push YOURFORK v3.3.x:auto-backport-of-pr-18860-on-v3.3.x

5. Create a PR against branch v3.3.x, I would have named this PR:

"Backport PR #18860 on branch v3.3.x"

And apply the correct labels and milestones.

Congratulation you did some good work ! Hopefully your backport PR will be tested by the continuous integration and merged soon!

If these instruction are inaccurate, feel free to suggest an improvement.