Intra-doc diagnostics are wrong with a disambiguator that's not in the value namespace

[jyn514]

I tried this code:

/// [type@std::io::not::here]
pub fn f() {}

I expected to the same diagnostic as without a disambiguator:

warning: unresolved link to `std::io::not::here`
 --> tmp.rs:2:6
  |
2 | /// [std::io::not::here]
  |      ^^^^^^^^^^^^^^^^^^ the module `io` has no inner item named `not`

Instead, rustdoc gave a diagnostic that made no sense:

warning: unresolved link to `std::io::not::here`
 --> tmp.rs:1:6
  |
1 | /// [type@std::io::not::here]
  |      ^^^^^^^^^^^^^^^^^^^^^^^ the module `io` has no type named `std::io`

Meta

rustc --version --verbose:

rustdoc 1.48.0-nightly (bbc677480 2020-09-18)

Relevant code:

rust/src/librustdoc/passes/collect_intra_doc_links.rs

Lines 209 to 230 in 8a13fc4

	// `variant_field` looks at 3 different path segments in a row.
	// But `NoAssocItem` assumes there are only 2. Check to see if there's
	// an intermediate segment that resolves.
	_ => {
	let intermediate_path = format!("{}::{}", path, variant_name);
	// NOTE: we have to be careful here, because we're already in `resolve`.
	// We know this doesn't recurse forever because we use a shorter path each time.
	// NOTE: this uses `TypeNS` because nothing else has a valid path segment after
	let kind = if let Some(intermediate) = self.check_full_res(
	TypeNS,
	&intermediate_path,
	module_id,
	current_item,
	extra_fragment,
	) {
	ResolutionFailure::NoAssocItem(intermediate, variant_field_name)
	} else {
	// Even with the shorter path, it didn't resolve, so say that.
	ResolutionFailure::NoAssocItem(ty_res, variant_name)
	};
	Err(kind.into())
	}

The issue is that variant_field is only called for the value namespace, but it's in charge of giving diagnostics for intermediate paths. That logic should instead be moved to fn resolution_failure.

[jyn514]

Another bug:

///  [f::A!]
pub fn f() {}

warning: unresolved link to `f::A`
 --> tmp.rs:3:7
  |
3 | ///  [f::A!]
  |       ^^^^^ no item named `f` in `tmp`