rustdoc: Link to the docs on namespaces when an unknown disambiguator is found

Author: jyn514

Diff for: src/librustdoc/passes/collect_intra_doc_links.rs

@@ -1924,7 +1924,20 @@ fn disambiguator_error(
     msg: &str,
 ) {
     diag_info.link_range = disambiguator_range;
-    report_diagnostic(cx.tcx, BROKEN_INTRA_DOC_LINKS, msg, &diag_info, |_diag, _sp| {});
+    report_diagnostic(cx.tcx, BROKEN_INTRA_DOC_LINKS, msg, &diag_info, |diag, _sp| {
+        let channel = match env!("CFG_RELEASE_CHANNEL") {
+            "stable" => env!("CFG_RELEASE_NUM"),
+            "beta" => "beta",
+            "nightly" | "dev" => "nightly",
+            // custom build of rustdoc maybe? link to the stable docs just in case
+            _ => "",
+        };
+        let msg = format!(
+            "see https://doc.rust-lang.org/{}/rustdoc/linking-to-items-by-name.html#namespaces-and-disambiguators for more info about disambiguators",
+            channel,
+        );
+        diag.note(&msg);
+    });
 }
 
 /// Report an ambiguity error, where there were multiple possible resolutions.

Diff for: src/test/rustdoc-ui/intra-doc/email-address-localhost.stderr

@@ -10,6 +10,7 @@ note: the lint level is defined here
 LL | #![deny(warnings)]
    |         ^^^^^^^^
    = note: `#[deny(rustdoc::broken_intra_doc_links)]` implied by `#[deny(warnings)]`
+   = note: see https://doc.rust-lang.org/nightly/rustdoc/linking-to-items-by-name.html#namespaces-and-disambiguators for more info about disambiguators
 
 error: aborting due to previous error
 

Diff for: src/test/rustdoc-ui/intra-doc/unknown-disambiguator.stderr

@@ -10,36 +10,47 @@ note: the lint level is defined here
 LL | #![deny(warnings)]
    |         ^^^^^^^^
    = note: `#[deny(rustdoc::broken_intra_doc_links)]` implied by `#[deny(warnings)]`
+   = note: see https://doc.rust-lang.org/nightly/rustdoc/linking-to-items-by-name.html#namespaces-and-disambiguators for more info about disambiguators
 
 error: unknown disambiguator `bar`
   --> $DIR/unknown-disambiguator.rs:3:35
    |
 LL | //! Linking to [foo@banana] and [`bar@banana!()`].
    |                                   ^^^
+   |
+   = note: see https://doc.rust-lang.org/nightly/rustdoc/linking-to-items-by-name.html#namespaces-and-disambiguators for more info about disambiguators
 
 error: unknown disambiguator `foo`
   --> $DIR/unknown-disambiguator.rs:9:34
    |
 LL | //! And with weird backticks: [``foo@hello``] [foo`@`hello].
    |                                  ^^^
+   |
+   = note: see https://doc.rust-lang.org/nightly/rustdoc/linking-to-items-by-name.html#namespaces-and-disambiguators for more info about disambiguators
 
 error: unknown disambiguator `foo`
   --> $DIR/unknown-disambiguator.rs:9:48
    |
 LL | //! And with weird backticks: [``foo@hello``] [foo`@`hello].
    |                                                ^^^
+   |
+   = note: see https://doc.rust-lang.org/nightly/rustdoc/linking-to-items-by-name.html#namespaces-and-disambiguators for more info about disambiguators
 
 error: unknown disambiguator ``
   --> $DIR/unknown-disambiguator.rs:6:31
    |
 LL | //! And to [no disambiguator](@nectarine) and [another](@apricot!()).
    |                               ^
+   |
+   = note: see https://doc.rust-lang.org/nightly/rustdoc/linking-to-items-by-name.html#namespaces-and-disambiguators for more info about disambiguators
 
 error: unknown disambiguator ``
   --> $DIR/unknown-disambiguator.rs:6:57
    |
 LL | //! And to [no disambiguator](@nectarine) and [another](@apricot!()).
    |                                                         ^
+   |
+   = note: see https://doc.rust-lang.org/nightly/rustdoc/linking-to-items-by-name.html#namespaces-and-disambiguators for more info about disambiguators
 
 error: aborting due to 6 previous errors