Optional set attributes of a function should be included when binding the set

[yunfachi]

Optional set attributes of a function should be included when binding the set

[roberth]

Unfortunately this is not something we can change without causing many expressions to break, which is a no-go for Nix.
Perhaps with a versioned language we could change this, but even then I'd be careful about making the entirety of the language (all versions) more complex.

An alternative that is feasible without versioning the language is to add a new syntax, such as #8636.

I'll add the breaking label so we can find this later, but I'll close it for now because it's not actionable for now.