Summary

set_constrained_layout/set_tight_layout is being deprecated in 3.6, but this makes it difficult (other than by version-gating) to work e.g. with matplotlib master (which I do on my personal setup) while keeping the code working with the last released version (3.5).

This also means that once mpl3.6 releases, essentially all projects that use this set_constrained_layout/set_tight_layout will need to "immediately" release a new version to hide that warning from end users.

Instead, perhaps that deprecation can be made pending for now, and turned into an actual deprecation in mpl 3.7 for release in 3.9, which leaves some buffer time for the change.

More generally, I think that when a new feature comes in in version X and is intended to replace an older approach, that old approach should not be deprecated in version X, but only in version X+1 at the latest (it can be pending-deprecation in version X), so that dependents can update during the life-cycle of version X, and so that people using master (before the release of X) do not run into the issue above.

Proposed fix

Make the deprecations pending.