Add an API to obtain all reachable items of a crate

[momvart]

TyCtxt currently provides an API to get all exported symbols of a crate. Still, there are some items in external crates that are not necessarily exported but are reachable and there is no direct way to get them. For example, some public generic functions provided by a library are like that.

Although it is possible to find them using methods like module_children, I want to request an API in TyCtxt that returns all reachable DefIds, a superset of exported_symbols.

pub fn reachable_symbols(
    self,
    key: CrateNum
) -> &'tcx [DefId]

[oli-obk]

Does https://doc.rust-lang.org/stable/nightly-rustc/rustc_middle/query/plumbing/struct.TyCtxtAt.html#method.collect_and_partition_mono_items contain everything you need?

[momvart]

Does https://doc.rust-lang.org/stable/nightly-rustc/rustc_middle/query/plumbing/struct.TyCtxtAt.html#method.collect_and_partition_mono_items contain everything you need?

It should. But it'll probably be just a workaround. In my case, in which I wanted to find the DefId of a specific function, module_children also worked. However, I'm proposing that maybe we should have a dedicated function for it that might benefit from caching as well.

BTW, as collect_and_partition_mono_items is meant for a different purpose, in addition to its expensive graph construction, it causes the MIR body to be built for all items (a last-step action IMO). A query for the list of DefIds is not expected to have such side effects.

To me rustc_metadata::rmeta::LazyTables.module_children_non_reexports looks suitable. A lazy iterator which flatmaps all values might work.

[oli-obk]

If it's not needed in rustc and can be emulated with existing functions, I think this should be implemented in the tool that needs it.

[momvart]

If it's not needed in rustc and can be emulated with existing functions, I think this should be implemented in the tool that needs it.

That's right. Maybe smir can provide it? Anyway, the data resides in CrateMetadata, which is protected from external access.

BTW, although it's just a printing function, but it looks like rustc_middle::ty::print::pretty::for_each_def is doing the recursion to obtain the same list.

[oli-obk]

If that function can be refactored into something reusable, great! Let's do that