Fix links to extern types in rustdoc (fixes #78777)

[lochsh]

r? @jyn514
Fixes #78777.
The initial fix we tried was:

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:

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.

[rust-highfive]

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[jyn514]

Thanks for working on this! @petrochenkov might want to look at the rustc_metadata change, but the work on intra-doc links looks great :)

[jyn514]

I would be interested to see if the following cause crashes:

• OpaqueTy
• AssocTy

(I got these from https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/def/enum.DefKind.html.)

AssocTy will definitely require larger refactors to fix properly (we'd have to call resolve_associated_trait_item recursively or something like that) but I think OpaqueTy may work without further changes. If so, please add a test case:

//! Link to [Opaque::Ty]
#![feature(type_alias_impl_trait)]

type Opaque = impl Trait;

pub trait Trait {
  type Ty;
}

impl Trait for () {
    type Ty = usize;
}

pub fn f() -> Opaque {
}

[lochsh]

Interestingly, I get the same behaviour for this test case whether DefKind::OpaqueTy is included in the match pattern or not:

warning: unresolved link to `Opaque::Ty`
 --> test.rs:1:14
  |
1 | //! Link to [Opaque::Ty]
  |              ^^^^^^^^^^ the type alias `Opaque` has no associated item named `Ty`
  |
  = note: `#[warn(broken_intra_doc_links)]` on by default

warning: 1 warning emitted

Here is the log output that seems relevant:

Opaque)))) in namespace TypeNS                                                                                                                                                                                                   [69/81]
DEBUG rustdoc::passes::collect_intra_doc_links looking for associated item named Ty for item DefId(0:3 ~ test[8787]::Opaque)
DEBUG rustdoc::passes::collect_intra_doc_links considering auto or blanket impl for trait Some(ResolvedPath { path: Path { global: false, res: Err, segments: [PathSegment { name: "Send", args: AngleBracketed { args: [], bindings: []
 } }] }, param_names: None, did: DefId(2:2047 ~ core[fe86]::marker::Send), is_generic: false })
DEBUG rustdoc::passes::collect_intra_doc_links considering auto or blanket impl for trait Some(ResolvedPath { path: Path { global: false, res: Err, segments: [PathSegment { name: "Sync", args: AngleBracketed { args: [], bindings: []
 } }] }, param_names: None, did: DefId(2:2059 ~ core[fe86]::marker::Sync), is_generic: false })
DEBUG rustdoc::passes::collect_intra_doc_links considering auto or blanket impl for trait Some(ResolvedPath { path: Path { global: false, res: Err, segments: [PathSegment { name: "Unpin", args: AngleBracketed { args: [], bindings: [
] } }] }, param_names: None, did: DefId(2:2088 ~ core[fe86]::marker::Unpin), is_generic: false })
DEBUG rustdoc::passes::collect_intra_doc_links considering auto or blanket impl for trait Some(ResolvedPath { path: Path { global: false, res: Err, segments: [PathSegment { name: "Freeze", args: AngleBracketed { args: [], bindings:
[] } }] }, param_names: None, did: DefId(2:2075 ~ core[fe86]::marker::Freeze), is_generic: false })
DEBUG rustdoc::passes::collect_intra_doc_links considering auto or blanket impl for trait Some(ResolvedPath { path: Path { global: false, res: Err, segments: [PathSegment { name: "UnwindSafe", args: AngleBracketed { args: [], bindin
gs: [] } }] }, param_names: None, did: DefId(1:3925 ~ std[7f8a]::panic::UnwindSafe), is_generic: false })
DEBUG rustdoc::passes::collect_intra_doc_links considering auto or blanket impl for trait Some(ResolvedPath { path: Path { global: false, res: Err, segments: [PathSegment { name: "RefUnwindSafe", args: AngleBracketed { args: [], bin
dings: [] } }] }, param_names: None, did: DefId(1:3926 ~ std[7f8a]::panic::RefUnwindSafe), is_generic: false })
DEBUG rustdoc::passes::collect_intra_doc_links considering auto or blanket impl for trait Some(ResolvedPath { path: Path { global: false, res: Err, segments: [PathSegment { name: "From", args: AngleBracketed { args: [Type(Generic("T
"))], bindings: [] } }] }, param_names: None, did: DefId(2:1965 ~ core[fe86]::convert::From), is_generic: false })
DEBUG rustdoc::passes::collect_intra_doc_links considering auto or blanket impl for trait Some(ResolvedPath { path: Path { global: false, res: Err, segments: [PathSegment { name: "Into", args: AngleBracketed { args: [Type(Generic("U
"))], bindings: [] } }] }, param_names: None, did: DefId(2:1962 ~ core[fe86]::convert::Into), is_generic: false })
DEBUG rustdoc::passes::collect_intra_doc_links considering auto or blanket impl for trait Some(ResolvedPath { path: Path { global: false, res: Err, segments: [PathSegment { name: "Borrow", args: AngleBracketed { args: [Type(Generic(
"T"))], bindings: [] } }] }, param_names: None, did: DefId(2:1722 ~ core[fe86]::borrow::Borrow), is_generic: false })
DEBUG rustdoc::passes::collect_intra_doc_links considering auto or blanket impl for trait Some(ResolvedPath { path: Path { global: false, res: Err, segments: [PathSegment { name: "BorrowMut", args: AngleBracketed { args: [Type(Gener
ic("T"))], bindings: [] } }] }, param_names: None, did: DefId(2:1725 ~ core[fe86]::borrow::BorrowMut), is_generic: false })
DEBUG rustdoc::passes::collect_intra_doc_links considering auto or blanket impl for trait Some(ResolvedPath { path: Path { global: false, res: Err, segments: [PathSegment { name: "TryFrom", args: AngleBracketed { args: [Type(Generic
("U"))], bindings: [] } }] }, param_names: None, did: DefId(2:1972 ~ core[fe86]::convert::TryFrom), is_generic: false })
DEBUG rustdoc::passes::collect_intra_doc_links considering auto or blanket impl for trait Some(ResolvedPath { path: Path { global: false, res: Err, segments: [PathSegment { name: "TryInto", args: AngleBracketed { args: [Type(Generic
("U"))], bindings: [] } }] }, param_names: None, did: DefId(2:1968 ~ core[fe86]::convert::TryInto), is_generic: false })
DEBUG rustdoc::passes::collect_intra_doc_links considering auto or blanket impl for trait Some(ResolvedPath { path: Path { global: false, res: Err, segments: [PathSegment { name: "Any", args: AngleBracketed { args: [], bindings: []
} }] }, param_names: None, did: DefId(2:2576 ~ core[fe86]::any::Any), is_generic: false })
DEBUG rustdoc::passes::collect_intra_doc_links considering traits {}
DEBUG rustdoc::passes::collect_intra_doc_links the candidates were []
DEBUG rustdoc::passes::collect_intra_doc_links got associated item kind None
DEBUG rustdoc::passes::collect_intra_doc_links Opaque::Ty resolved to Err(()) in namespace ValueNS
DEBUG rustdoc::passes::collect_intra_doc_links Opaque resolved to Ok((Path { span: test.rs:1:1: 1:1 (#0), segments: [PathSegment { ident: Opaque#0, id: NodeId(38), args: None }], tokens: None }, Def(TyAlias, DefId(0:3 ~ test[8787]::
Opaque)))) in namespace TypeNS
DEBUG rustdoc::passes::collect_intra_doc_links looking for associated item named Ty for item DefId(0:3 ~ test[8787]::Opaque)
DEBUG rustdoc::passes::collect_intra_doc_links considering traits {}
DEBUG rustdoc::passes::collect_intra_doc_links the candidates were []
DEBUG rustdoc::passes::collect_intra_doc_links got associated item kind None
DEBUG rustdoc::passes::collect_intra_doc_links looking for variants or fields named Ty for DefId(0:3 ~ test[8787]::Opaque)
DEBUG rustdoc::passes::collect_intra_doc_links looking for enum variant Opaque::Ty
DEBUG rustdoc::passes::collect_intra_doc_links Opaque resolved to Ok((Path { span: test.rs:1:1: 1:1 (#0), segments: [PathSegment { ident: Opaque#0, id: NodeId(39), args: None }], tokens: None }, Def(TyAlias, DefId(0:3 ~ test[8787]::
Opaque)))) in namespace TypeNS
DEBUG rustdoc::passes::collect_intra_doc_links found partial_res=Def(TyAlias, DefId(0:3 ~ test[8787]::Opaque))

[jyn514]

Hmm, ok. The bug here is that considering traits {} should have Trait, but we can fix it later, I'm not sure this is actually something rustdoc should do since impl Trait is supposed to hide which type is being returned.

[jyn514]

@bors r+ rollup

Thanks for working on this!

[bors]

📌 Commit 32cd4bc has been approved by jyn514