[rustdoc] List matching impls on type aliases by GuillaumeGomez · Pull Request #...

I'm sure threading this parameter through all these function calls is probably cheaper than using let is_alias = tcx.def_kind(it) == DefKind::TyAlias and using let aliased_type = tcx.type_of(it) to resolve it, since the calling functions already have this information.

But is pulling the information out of TyCtxt expensive enough to be worth having a function with seven parameters?

We need a variable to tell us that this is an alias. From this, since we already have the DefId, why not using it directly?

EDIT: Just re-read your comment. I'm not sure to like it much simply because we re-compute an information we already have. But that's pretty much my only argument against it. ^^'

I edited my comment, I don't know how but I misread your comment the first time. Sorry about that.

There's not a lot of computation going into it, though. It's looking information up in a hash table.

It's not the part worrying me but since I can't put the finger on it, I'll just remove the newly added argument and let's see how it goes. :)

Ah found it! I need it because of Some(aliased_type) => cache.impls.get(&aliased_type).unwrap_or(&empty),. We can't retrieve the DefId easily from a Ty. The only method I found to get it is ty_adt_id but it doesn't cover all the cases we need.

That makes sense. Thanks for the info!

Having aliased_type separately here feels off to me and may at least deserve a comment, but that's unrelated to the type system itself so I am fine with that.

The doc comment for aliased_type is already on the function. ;)