So, it seems a bunch of the s2n proofs use llvm_struct. Should we fix them, or put this off? (and if we put it off, what eventually changes? it seems unlikely we'll drop the s2n proofs entirely from the testing)

While it would be nice to fix the s2n proofs to use llvm_alias instead of llvm_struct, I am rather surprised that it's strictly required here. Isn't the point of this PR to deprecate llvm_struct rather than to remove it outright? If llvm_struct is only deprecated, then why is code suddenly failing to run?

Because when you mark something deprecated, you then have to use enable_deprecated to be allowed to see it. Which seems like the wrong thing, so maybe the first step is to rearrange the framework...

Because when you mark something deprecated, you then have to use enable_deprecated to be allowed to see it.

Oh wow, I was blissfully ignorant of this. That certainly feels like a strange design—I would argue it makes much more sense for seeing deprecated functions to be opt-out rather than opt-in.

the first step is to rearrange the framework

I agree. Shall we open a separate issue about this? It feels as though we'd want disable_{experimental,deprecated} counterparts to the existing enable_{experimental,deprecated} commands, and then change the deprecated commands to be enabled by default.

It's more complicated than that because I don't think we want the existing not-visible deprecated functions to come back to life.

Anyway I opened #2184 for this.

I force-pushed it to split the changes to prepare for deprecation (clearing out the uses of llvm_struct and fixing the bad reference in the manual) from the actual deprecation (which is stalled) because the former can be merged now. And I rebased it on HEAD.

I have rebased this on head again after merging #2193, which contained the cleanup part of what was previously in this changeset. (Now this branch has only the actual deprecation setting, which is going to change again after #2184 makes it possible to have warn-only deprecation, and the changelog entry.)