Sharp edge when dropping columns

[This is my first message on a PG mailing list, here's hoping I'm not breaching etiquette somehow]

Bonjour,

I'd like to report a sharp edge which caused downtime in my production application: dropping a column which is INCLUDEd in an index drops the index.

In the past, I have included a field in some of my indexes so that related queries can be performed as an index-only scan. This field was later deprecated. When the related column was ultimately dropped, the performance of the initial queries ground to a halt because the underlying index had been dropped.

I found this behavior unexpected. I think preventing the index from being dropped in some circumstances would make this less surprising. The exact circumstances likely need to be hashed out if there is a consensus that this is a (minor) problem.

Please find below a simple reproduction script:

Thank you for reading,

Quentin de Metz