Fix links to extern types in rustdoc (fixes#78777)
r? `@jyn514`
Fixes#78777.
The initial fix we tried was:
```diff
diff --git a/src/librustdoc/passes/collect_intra_doc_links.rs b/src/librustdoc/passes/collect_intra_doc_links.rs
index 8be9482acff..c4b7086fdb1 100644
--- a/src/librustdoc/passes/collect_intra_doc_links.rs
+++ b/src/librustdoc/passes/collect_intra_doc_links.rs
`@@` -433,8 +433,9 `@@` impl<'a, 'tcx> LinkCollector<'a, 'tcx> {
Res::PrimTy(prim) => Some(
self.resolve_primitive_associated_item(prim, ns, module_id, item_name, item_str),
),
- Res::Def(DefKind::Struct | DefKind::Union | DefKind::Enum | DefKind::TyAlias, did) => {
+ Res::Def(kind, did) if kind.ns() == Some(Namespace::TypeNS) => {
debug!("looking for associated item named {} for item {:?}", item_name, did);
+
// Checks if item_name belongs to `impl SomeItem`
let assoc_item = cx
.tcx
```
However, this caused traits to be matched, resulting in a panic when `resolve_associated_trait_item` is called further down in this function.
This PR also adds an error message for that panic. Currently it will look something like:
```rust
thread 'rustc' panicked at 'Not a type: DefIndex(8624)', compiler/rustc_metadata/src/rmeta/decoder.rs:951:32
```
I wasn't sure how to get a better debug output than `DefIndex(...)`, and am open to suggestions.
5d428cae7d