Only report reference-style link errors once

Co-authored-by: Joshua Nelson <joshua@yottadb.com>

6 files changed, 175 insertions, 67 deletions

diff --git a/src/librustdoc/html/markdown.rs b/src/librustdoc/html/markdown.rs
index 07744139605..cc6ce3115b6 100644
--- a/src/librustdoc/html/markdown.rs
+++ b/src/librustdoc/html/markdown.rs
@@ -37,7 +37,9 @@ use crate::doctest;
 use crate::html::highlight;
 use crate::html::toc::TocBuilder;
 
-use pulldown_cmark::{html, BrokenLink, CodeBlockKind, CowStr, Event, Options, Parser, Tag};
+use pulldown_cmark::{
+    html, BrokenLink, CodeBlockKind, CowStr, Event, LinkType, Options, Parser, Tag,
+};
 
 #[cfg(test)]
 mod tests;
@@ -327,8 +329,6 @@ impl<'a, I: Iterator<Item = Event<'a>>> Iterator for LinkReplacer<'a, I> {
     type Item = Event<'a>;
 
     fn next(&mut self) -> Option<Self::Item> {
-        use pulldown_cmark::LinkType;
-
         let mut event = self.inner.next();
 
         // Replace intra-doc links and remove disambiguators from shortcut links (`[fn@f]`).
@@ -1123,7 +1123,13 @@ crate fn plain_text_summary(md: &str) -> String {
     s
 }
 
-crate fn markdown_links(md: &str) -> Vec<(String, Range<usize>)> {
+crate struct MarkdownLink {
+    pub kind: LinkType,
+    pub link: String,
+    pub range: Range<usize>,
+}
+
+crate fn markdown_links(md: &str) -> Vec<MarkdownLink> {
     if md.is_empty() {
         return vec![];
     }
@@ -1163,7 +1169,11 @@ crate fn markdown_links(md: &str) -> Vec<(String, Range<usize>)> {
 
     let mut push = |link: BrokenLink<'_>| {
         let span = span_for_link(&CowStr::Borrowed(link.reference), link.span);
-        links.borrow_mut().push((link.reference.to_owned(), span));
+        links.borrow_mut().push(MarkdownLink {
+            kind: LinkType::ShortcutUnknown,
+            link: link.reference.to_owned(),
+            range: span,
+        });
         None
     };
     let p = Parser::new_with_broken_link_callback(md, opts(), Some(&mut push)).into_offset_iter();
@@ -1174,10 +1184,10 @@ crate fn markdown_links(md: &str) -> Vec<(String, Range<usize>)> {
     let iter = Footnotes::new(HeadingLinks::new(p, None, &mut ids));
 
     for ev in iter {
-        if let Event::Start(Tag::Link(_, dest, _)) = ev.0 {
+        if let Event::Start(Tag::Link(kind, dest, _)) = ev.0 {
             debug!("found link: {}", dest);
             let span = span_for_link(&dest, ev.1);
-            links.borrow_mut().push((dest.into_string(), span));
+            links.borrow_mut().push(MarkdownLink { kind, link: dest.into_string(), range: span });
         }
     }
 
diff --git a/src/librustdoc/passes/collect_intra_doc_links.rs b/src/librustdoc/passes/collect_intra_doc_links.rs
index 6fcec6946ae..0cefbb34791 100644
--- a/src/librustdoc/passes/collect_intra_doc_links.rs
+++ b/src/librustdoc/passes/collect_intra_doc_links.rs
@@ -25,6 +25,8 @@ use rustc_span::symbol::Symbol;
 use rustc_span::DUMMY_SP;
 use smallvec::{smallvec, SmallVec};
 
+use pulldown_cmark::LinkType;
+
 use std::borrow::Cow;
 use std::cell::Cell;
 use std::convert::{TryFrom, TryInto};
@@ -34,7 +36,7 @@ use std::ops::Range;
 use crate::clean::{self, utils::find_nearest_parent_module, Crate, Item, ItemLink, PrimitiveType};
 use crate::core::DocContext;
 use crate::fold::DocFolder;
-use crate::html::markdown::markdown_links;
+use crate::html::markdown::{markdown_links, MarkdownLink};
 use crate::passes::Pass;
 
 use super::span_of_attrs;
@@ -265,8 +267,9 @@ struct LinkCollector<'a, 'tcx> {
     /// because `clean` and the disambiguator code expect them to be different.
     /// See the code for associated items on inherent impls for details.
     kind_side_channel: Cell<Option<(DefKind, DefId)>>,
-    /// Cache the resolved links so we can avoid resolving (and emitting errors for) the same link
-    visited_links: FxHashMap<ResolutionInfo, CachedLink>,
+    /// Cache the resolved links so we can avoid resolving (and emitting errors for) the same link.
+    /// The link will be `None` if it could not be resolved (i.e. the error was cached).
+    visited_links: FxHashMap<ResolutionInfo, Option<CachedLink>>,
 }
 
 impl<'a, 'tcx> LinkCollector<'a, 'tcx> {
@@ -901,16 +904,8 @@ impl<'a, 'tcx> DocFolder for LinkCollector<'a, 'tcx> {
             };
             // NOTE: if there are links that start in one crate and end in another, this will not resolve them.
             // This is a degenerate case and it's not supported by rustdoc.
-            for (ori_link, link_range) in markdown_links(&doc) {
-                let link = self.resolve_link(
-                    &item,
-                    &doc,
-                    &self_name,
-                    parent_node,
-                    krate,
-                    ori_link,
-                    link_range,
-                );
+            for md_link in markdown_links(&doc) {
+                let link = self.resolve_link(&item, &doc, &self_name, parent_node, krate, md_link);
                 if let Some(link) = link {
                     item.attrs.links.push(link);
                 }
@@ -942,27 +937,26 @@ impl LinkCollector<'_, '_> {
         self_name: &Option<String>,
         parent_node: Option<DefId>,
         krate: CrateNum,
-        ori_link: String,
-        link_range: Range<usize>,
+        ori_link: MarkdownLink,
     ) -> Option<ItemLink> {
-        trace!("considering link '{}'", ori_link);
+        trace!("considering link '{}'", ori_link.link);
 
         // Bail early for real links.
-        if ori_link.contains('/') {
+        if ori_link.link.contains('/') {
             return None;
         }
 
         // [] is mostly likely not supposed to be a link
-        if ori_link.is_empty() {
+        if ori_link.link.is_empty() {
             return None;
         }
 
         let cx = self.cx;
-        let link = ori_link.replace("`", "");
+        let link = ori_link.link.replace("`", "");
         let parts = link.split('#').collect::<Vec<_>>();
         let (link, extra_fragment) = if parts.len() > 2 {
             // A valid link can't have multiple #'s
-            anchor_failure(cx, &item, &link, dox, link_range, AnchorFailure::MultipleAnchors);
+            anchor_failure(cx, &item, &link, dox, ori_link.range, AnchorFailure::MultipleAnchors);
             return None;
         } else if parts.len() == 2 {
             if parts[0].trim().is_empty() {
@@ -1018,7 +1012,7 @@ impl LinkCollector<'_, '_> {
                 path_str,
                 disambiguator,
                 dox,
-                link_range,
+                ori_link.range,
                 smallvec![ResolutionFailure::NoParentItem],
             );
             return None;
@@ -1058,7 +1052,7 @@ impl LinkCollector<'_, '_> {
                         path_str,
                         disambiguator,
                         dox,
-                        link_range,
+                        ori_link.range,
                         smallvec![err_kind],
                     );
                     return None;
@@ -1074,15 +1068,22 @@ impl LinkCollector<'_, '_> {
             return None;
         }
 
-        let key = ResolutionInfo {
-            module_id,
-            dis: disambiguator,
-            path_str: path_str.to_owned(),
-            extra_fragment,
+        let diag_info = DiagnosticInfo {
+            item,
+            dox,
+            ori_link: &ori_link.link,
+            link_range: ori_link.range.clone(),
         };
-        let diag =
-            DiagnosticInfo { item, dox, ori_link: &ori_link, link_range: link_range.clone() };
-        let (mut res, mut fragment) = self.resolve_with_disambiguator_cached(key, diag)?;
+        let (mut res, mut fragment) = self.resolve_with_disambiguator_cached(
+            ResolutionInfo {
+                module_id,
+                dis: disambiguator,
+                path_str: path_str.to_owned(),
+                extra_fragment,
+            },
+            diag_info,
+            matches!(ori_link.kind, LinkType::Reference | LinkType::Shortcut),
+        )?;
 
         // Check for a primitive which might conflict with a module
         // Report the ambiguity and require that the user specify which one they meant.
@@ -1101,7 +1102,7 @@ impl LinkCollector<'_, '_> {
                             &item,
                             path_str,
                             dox,
-                            link_range,
+                            ori_link.range,
                             AnchorFailure::RustdocAnchorConflict(prim),
                         );
                         return None;
@@ -1111,7 +1112,7 @@ impl LinkCollector<'_, '_> {
                 } else {
                     // `[char]` when a `char` module is in scope
                     let candidates = vec![res, prim];
-                    ambiguity_error(cx, &item, path_str, dox, link_range, candidates);
+                    ambiguity_error(cx, &item, path_str, dox, ori_link.range, candidates);
                     return None;
                 }
             }
@@ -1129,14 +1130,22 @@ impl LinkCollector<'_, '_> {
                     specified.descr()
                 );
                 diag.note(&note);
-                suggest_disambiguator(resolved, diag, path_str, dox, sp, &link_range);
+                suggest_disambiguator(resolved, diag, path_str, dox, sp, &ori_link.range);
             };
-            report_diagnostic(cx, BROKEN_INTRA_DOC_LINKS, &msg, &item, dox, &link_range, callback);
+            report_diagnostic(
+                cx,
+                BROKEN_INTRA_DOC_LINKS,
+                &msg,
+                &item,
+                dox,
+                &ori_link.range,
+                callback,
+            );
         };
         match res {
             Res::Primitive(_) => match disambiguator {
                 Some(Disambiguator::Primitive | Disambiguator::Namespace(_)) | None => {
-                    Some(ItemLink { link: ori_link, link_text, did: None, fragment })
+                    Some(ItemLink { link: ori_link.link, link_text, did: None, fragment })
                 }
                 Some(other) => {
                     report_mismatch(other, Disambiguator::Primitive);
@@ -1179,11 +1188,11 @@ impl LinkCollector<'_, '_> {
                     if self.cx.tcx.privacy_access_levels(LOCAL_CRATE).is_exported(hir_src)
                         && !self.cx.tcx.privacy_access_levels(LOCAL_CRATE).is_exported(hir_dst)
                     {
-                        privacy_error(cx, &item, &path_str, dox, link_range);
+                        privacy_error(cx, &item, &path_str, dox, &ori_link);
                     }
                 }
                 let id = clean::register_res(cx, rustc_hir::def::Res::Def(kind, id));
-                Some(ItemLink { link: ori_link, link_text, did: Some(id), fragment })
+                Some(ItemLink { link: ori_link.link, link_text, did: Some(id), fragment })
             }
         }
     }
@@ -1192,28 +1201,47 @@ impl LinkCollector<'_, '_> {
         &mut self,
         key: ResolutionInfo,
         diag: DiagnosticInfo<'_>,
+        cache_resolution_failure: bool,
     ) -> Option<(Res, Option<String>)> {
         // Try to look up both the result and the corresponding side channel value
         if let Some(ref cached) = self.visited_links.get(&key) {
-            self.kind_side_channel.set(cached.side_channel);
-            return Some(cached.res.clone());
+            match cached {
+                Some(cached) => {
+                    self.kind_side_channel.set(cached.side_channel.clone());
+                    return Some(cached.res.clone());
+                }
+                None if cache_resolution_failure => return None,
+                None => {
+                    // Although we hit the cache and found a resolution error, this link isn't
+                    // supposed to cache those. Run link resolution again to emit the expected
+                    // resolution error.
+                }
+            }
         }
 
         let res = self.resolve_with_disambiguator(&key, diag);
 
         // Cache only if resolved successfully - don't silence duplicate errors
-        if let Some(res) = &res {
+        if let Some(res) = res {
             // Store result for the actual namespace
             self.visited_links.insert(
                 key,
-                CachedLink {
+                Some(CachedLink {
                     res: res.clone(),
                     side_channel: self.kind_side_channel.clone().into_inner(),
-                },
+                }),
             );
-        }
 
-        res
+            Some(res)
+        } else {
+            if cache_resolution_failure {
+                // For reference-style links we only want to report one resolution error
+                // so let's cache them as well.
+                self.visited_links.insert(key, None);
+            }
+
+            None
+        }
     }
 
     /// After parsing the disambiguator, resolve the main part of the link.
@@ -1964,13 +1992,7 @@ fn suggest_disambiguator(
 }
 
 /// Report a link from a public item to a private one.
-fn privacy_error(
-    cx: &DocContext<'_>,
-    item: &Item,
-    path_str: &str,
-    dox: &str,
-    link_range: Range<usize>,
-) {
+fn privacy_error(cx: &DocContext<'_>, item: &Item, path_str: &str, dox: &str, link: &MarkdownLink) {
     let sym;
     let item_name = match item.name {
         Some(name) => {
@@ -1982,7 +2004,7 @@ fn privacy_error(
     let msg =
         format!("public documentation for `{}` links to private item `{}`", item_name, path_str);
 
-    report_diagnostic(cx, PRIVATE_INTRA_DOC_LINKS, &msg, item, dox, &link_range, |diag, sp| {
+    report_diagnostic(cx, PRIVATE_INTRA_DOC_LINKS, &msg, item, dox, &link.range, |diag, sp| {
         if let Some(sp) = sp {
             diag.span_label(sp, "this item is private");
         }
diff --git a/src/test/rustdoc-ui/reference-link-reports-error-once.rs b/src/test/rustdoc-ui/reference-link-reports-error-once.rs
new file mode 100644
index 00000000000..7957ee373c4
--- /dev/null
+++ b/src/test/rustdoc-ui/reference-link-reports-error-once.rs
@@ -0,0 +1,20 @@
+#![deny(broken_intra_doc_links)]
+
+/// Links to [a] [link][a]
+/// And also a [third link][a]
+/// And also a [reference link][b]
+///
+/// Other links to the same target should still emit error: [ref] //~ERROR unresolved link to `ref`
+/// Duplicate [ref] //~ERROR unresolved link to `ref`
+///
+/// Other links to other targets should still emit error: [ref2] //~ERROR unresolved link to `ref2`
+/// Duplicate [ref2] //~ERROR unresolved link to `ref2`
+///
+/// [a]: ref
+//~^ ERROR unresolved link to `ref`
+/// [b]: ref2
+//~^ ERROR unresolved link to
+
+/// [ref][]
+//~^ ERROR unresolved link
+pub fn f() {}
diff --git a/src/test/rustdoc-ui/reference-link-reports-error-once.stderr b/src/test/rustdoc-ui/reference-link-reports-error-once.stderr
new file mode 100644
index 00000000000..218eb334a6f
--- /dev/null
+++ b/src/test/rustdoc-ui/reference-link-reports-error-once.stderr
@@ -0,0 +1,63 @@
+error: unresolved link to `ref`
+  --> $DIR/reference-link-reports-error-once.rs:13:10
+   |
+LL | /// [a]: ref
+   |          ^^^ no item named `ref` in scope
+   |
+note: the lint level is defined here
+  --> $DIR/reference-link-reports-error-once.rs:1:9
+   |
+LL | #![deny(broken_intra_doc_links)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^
+   = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
+
+error: unresolved link to `ref2`
+  --> $DIR/reference-link-reports-error-once.rs:15:10
+   |
+LL | /// [b]: ref2
+   |          ^^^^ no item named `ref2` in scope
+   |
+   = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
+
+error: unresolved link to `ref`
+  --> $DIR/reference-link-reports-error-once.rs:7:62
+   |
+LL | /// Other links to the same target should still emit error: [ref]
+   |                                                              ^^^ no item named `ref` in scope
+   |
+   = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
+
+error: unresolved link to `ref`
+  --> $DIR/reference-link-reports-error-once.rs:8:16
+   |
+LL | /// Duplicate [ref]
+   |                ^^^ no item named `ref` in scope
+   |
+   = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
+
+error: unresolved link to `ref2`
+  --> $DIR/reference-link-reports-error-once.rs:10:60
+   |
+LL | /// Other links to other targets should still emit error: [ref2]
+   |                                                            ^^^^ no item named `ref2` in scope
+   |
+   = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
+
+error: unresolved link to `ref2`
+  --> $DIR/reference-link-reports-error-once.rs:11:16
+   |
+LL | /// Duplicate [ref2]
+   |                ^^^^ no item named `ref2` in scope
+   |
+   = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
+
+error: unresolved link to `ref`
+  --> $DIR/reference-link-reports-error-once.rs:18:6
+   |
+LL | /// [ref][]
+   |      ^^^ no item named `ref` in scope
+   |
+   = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
+
+error: aborting due to 7 previous errors
+
diff --git a/src/test/rustdoc-ui/reference-links.rs b/src/test/rustdoc-ui/reference-links.rs
index 7c1a79722c9..6e00b9f0fa1 100644
--- a/src/test/rustdoc-ui/reference-links.rs
+++ b/src/test/rustdoc-ui/reference-links.rs
@@ -4,4 +4,3 @@
 //!
 //! [a]: std::process::Comman
 //~^ ERROR unresolved
-//~| ERROR unresolved
diff --git a/src/test/rustdoc-ui/reference-links.stderr b/src/test/rustdoc-ui/reference-links.stderr
index 6ba73fbdb00..3df89df21b4 100644
--- a/src/test/rustdoc-ui/reference-links.stderr
+++ b/src/test/rustdoc-ui/reference-links.stderr
@@ -10,11 +10,5 @@ note: the lint level is defined here
 LL | #![deny(broken_intra_doc_links)]
    |         ^^^^^^^^^^^^^^^^^^^^^^
 
-error: unresolved link to `std::process::Comman`
-  --> $DIR/reference-links.rs:5:10
-   |
-LL | //! [a]: std::process::Comman
-   |          ^^^^^^^^^^^^^^^^^^^^ no item named `Comman` in module `process`
-
-error: aborting due to 2 previous errors
+error: aborting due to previous error