rustdoc: improve refdef handling in the unresolved link lint

This commit takes advantage of a feature in pulldown-cmark that
makes the list of link definitions available to the consuming
application. It produces unresolved link warnings for refdefs
that aren't used, and can now produce exact spans for the dest
even when it has escapes.

4 files changed, 162 insertions, 35 deletions

diff --git a/compiler/rustc_resolve/src/rustdoc.rs b/compiler/rustc_resolve/src/rustdoc.rs
index fecb9735019..52aaab77ebe 100644
--- a/compiler/rustc_resolve/src/rustdoc.rs
+++ b/compiler/rustc_resolve/src/rustdoc.rs
@@ -7,7 +7,7 @@ use pulldown_cmark::{
 use rustc_ast as ast;
 use rustc_ast::attr::AttributeExt;
 use rustc_ast::util::comments::beautify_doc_string;
-use rustc_data_structures::fx::FxIndexMap;
+use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
 use rustc_middle::ty::TyCtxt;
 use rustc_span::def_id::DefId;
 use rustc_span::{DUMMY_SP, InnerSpan, Span, Symbol, kw, sym};
@@ -422,9 +422,11 @@ fn parse_links<'md>(doc: &'md str) -> Vec<Box<str>> {
     );
     let mut links = Vec::new();
 
+    let mut refids = FxHashSet::default();
+
     while let Some(event) = event_iter.next() {
         match event {
-            Event::Start(Tag::Link { link_type, dest_url, title: _, id: _ })
+            Event::Start(Tag::Link { link_type, dest_url, title: _, id })
                 if may_be_doc_link(link_type) =>
             {
                 if matches!(
@@ -439,6 +441,12 @@ fn parse_links<'md>(doc: &'md str) -> Vec<Box<str>> {
                         links.push(display_text);
                     }
                 }
+                if matches!(
+                    link_type,
+                    LinkType::Reference | LinkType::Shortcut | LinkType::Collapsed
+                ) {
+                    refids.insert(id);
+                }
 
                 links.push(preprocess_link(&dest_url));
             }
@@ -446,6 +454,12 @@ fn parse_links<'md>(doc: &'md str) -> Vec<Box<str>> {
         }
     }
 
+    for (label, refdef) in event_iter.reference_definitions().iter() {
+        if !refids.contains(label) {
+            links.push(preprocess_link(&refdef.dest));
+        }
+    }
+
     links
 }
 
diff --git a/src/librustdoc/html/markdown.rs b/src/librustdoc/html/markdown.rs
index bd8eda2fed6..d9e49577d39 100644
--- a/src/librustdoc/html/markdown.rs
+++ b/src/librustdoc/html/markdown.rs
@@ -38,7 +38,7 @@ use std::sync::{Arc, Weak};
 use pulldown_cmark::{
     BrokenLink, CodeBlockKind, CowStr, Event, LinkType, Options, Parser, Tag, TagEnd, html,
 };
-use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
 use rustc_errors::{Diag, DiagMessage};
 use rustc_hir::def_id::LocalDefId;
 use rustc_middle::ty::TyCtxt;
@@ -1763,6 +1763,46 @@ pub(crate) fn markdown_links<'md, R>(
         }
     };
 
+    let span_for_refdef = |link: &CowStr<'_>, span: Range<usize>| {
+        // We want to underline the link's definition, but `span` will point at the entire refdef.
+        // Skip the label, then try to find the entire URL.
+        let mut square_brace_count = 0;
+        let mut iter = md.as_bytes()[span.start..span.end].iter().copied().enumerate();
+        for (_i, c) in &mut iter {
+            match c {
+                b':' if square_brace_count == 0 => break,
+                b'[' => square_brace_count += 1,
+                b']' => square_brace_count -= 1,
+                _ => {}
+            }
+        }
+        while let Some((i, c)) = iter.next() {
+            if c == b'<' {
+                while let Some((j, c)) = iter.next() {
+                    match c {
+                        b'\\' => {
+                            let _ = iter.next();
+                        }
+                        b'>' => {
+                            return MarkdownLinkRange::Destination(
+                                i + 1 + span.start..j + span.start,
+                            );
+                        }
+                        _ => {}
+                    }
+                }
+            } else if !c.is_ascii_whitespace() {
+                while let Some((j, c)) = iter.next() {
+                    if c.is_ascii_whitespace() {
+                        return MarkdownLinkRange::Destination(i + span.start..j + span.start);
+                    }
+                }
+                return MarkdownLinkRange::Destination(i + span.start..span.end);
+            }
+        }
+        span_for_link(link, span)
+    };
+
     let span_for_offset_backward = |span: Range<usize>, open: u8, close: u8| {
         let mut open_brace = !0;
         let mut close_brace = !0;
@@ -1844,9 +1884,16 @@ pub(crate) fn markdown_links<'md, R>(
     .into_offset_iter();
     let mut links = Vec::new();
 
+    let mut refdefs = FxIndexMap::default();
+    for (label, refdef) in event_iter.reference_definitions().iter() {
+        refdefs.insert(label.to_string(), (false, refdef.dest.to_string(), refdef.span.clone()));
+    }
+
     for (event, span) in event_iter {
         match event {
-            Event::Start(Tag::Link { link_type, dest_url, .. }) if may_be_doc_link(link_type) => {
+            Event::Start(Tag::Link { link_type, dest_url, id, .. })
+                if may_be_doc_link(link_type) =>
+            {
                 let range = match link_type {
                     // Link is pulled from the link itself.
                     LinkType::ReferenceUnknown | LinkType::ShortcutUnknown => {
@@ -1856,7 +1903,12 @@ pub(crate) fn markdown_links<'md, R>(
                     LinkType::Inline => span_for_offset_backward(span, b'(', b')'),
                     // Link is pulled from elsewhere in the document.
                     LinkType::Reference | LinkType::Collapsed | LinkType::Shortcut => {
-                        span_for_link(&dest_url, span)
+                        if let Some((is_used, dest_url, span)) = refdefs.get_mut(&id[..]) {
+                            *is_used = true;
+                            span_for_refdef(&CowStr::from(&dest_url[..]), span.clone())
+                        } else {
+                            span_for_link(&dest_url, span)
+                        }
                     }
                     LinkType::Autolink | LinkType::Email => unreachable!(),
                 };
@@ -1873,6 +1925,18 @@ pub(crate) fn markdown_links<'md, R>(
         }
     }
 
+    for (_label, (is_used, dest_url, span)) in refdefs.into_iter() {
+        if !is_used
+            && let Some(link) = preprocess_link(MarkdownLink {
+                kind: LinkType::Reference,
+                range: span_for_refdef(&CowStr::from(&dest_url[..]), span),
+                link: dest_url,
+            })
+        {
+            links.push(link);
+        }
+    }
+
     links
 }
 
diff --git a/tests/rustdoc-ui/intra-doc/weird-syntax.rs b/tests/rustdoc-ui/intra-doc/weird-syntax.rs
index ca18842fb21..d2a922b2b62 100644
--- a/tests/rustdoc-ui/intra-doc/weird-syntax.rs
+++ b/tests/rustdoc-ui/intra-doc/weird-syntax.rs
@@ -117,24 +117,49 @@ pub struct WLinkToCloneWithUnmatchedEscapedCloseParenAndDoubleSpace;
 
 // References
 
-/// The [cln][] link here is going to be unresolved, because `Clone()` gets rejected //~ERROR link
-/// in Markdown for not being URL-shaped enough.
-///
-/// [cln]: Clone() //~ERROR link
+/// The [cln][] link here is going to be unresolved, because `Clone()` gets
+//~^ ERROR link
+/// rejected in Markdown for not being URL-shaped enough.
+/// [cln]: Clone()
+//~^ ERROR link
 pub struct LinkToCloneWithParensInReference;
 
-/// The [cln][] link here is going to be unresolved, because `struct@Clone` gets //~ERROR link
-/// rejected in Markdown for not being URL-shaped enough.
+/// The [cln][] link here is going to produce a good inline suggestion
 ///
-/// [cln]: struct@Clone //~ERROR link
+/// [cln]: struct@Clone
+//~^ ERROR link
 pub struct LinkToCloneWithWrongPrefix;
 
-/// The [cln][] link here will produce a plain text suggestion //~ERROR link
+/// The [cln][] link here will produce a good inline suggestion
 ///
 /// [cln]: Clone\(\)
+//~^ ERROR link
 pub struct LinkToCloneWithEscapedParensInReference;
 
-/// The [cln][] link here will produce a plain text suggestion //~ERROR link
+/// The [cln][] link here will produce a good inline suggestion
 ///
 /// [cln]: struct\@Clone
+//~^ ERROR link
 pub struct LinkToCloneWithEscapedAtsInReference;
+
+
+/// This link reference definition isn't used, but since it is still parsed,
+/// it should still produce a warning.
+///
+/// [cln]: struct\@Clone
+//~^ ERROR link
+pub struct UnusedLinkToCloneReferenceDefinition;
+
+/// <https://github.com/rust-lang/rust/issues/133150>
+///
+/// - [`SDL_PROP_WINDOW_CREATE_COCOA_WINDOW_POINTER`]: the
+//~^ ERROR link
+///   `(__unsafe_unretained)` NSWindow associated with the window, if you want
+///   to wrap an existing window.
+/// - [`SDL_PROP_WINDOW_CREATE_COCOA_VIEW_POINTER`]: the `(__unsafe_unretained)`
+///   NSView associated with the window, defaults to `[window contentView]`
+pub fn a() {}
+#[allow(nonstandard_style)]
+pub struct SDL_PROP_WINDOW_CREATE_COCOA_WINDOW_POINTER;
+#[allow(nonstandard_style)]
+pub struct SDL_PROP_WINDOW_CREATE_COCOA_VIEW_POINTER;
diff --git a/tests/rustdoc-ui/intra-doc/weird-syntax.stderr b/tests/rustdoc-ui/intra-doc/weird-syntax.stderr
index 1381c1b31eb..ad813f0f9b6 100644
--- a/tests/rustdoc-ui/intra-doc/weird-syntax.stderr
+++ b/tests/rustdoc-ui/intra-doc/weird-syntax.stderr
@@ -230,7 +230,7 @@ LL | /// [w](Clone  \))
 error: unresolved link to `cln`
   --> $DIR/weird-syntax.rs:120:10
    |
-LL | /// The [cln][] link here is going to be unresolved, because `Clone()` gets rejected
+LL | /// The [cln][] link here is going to be unresolved, because `Clone()` gets
    |          ^^^ no item named `cln` in scope
    |
    = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
@@ -243,37 +243,61 @@ LL | /// [cln]: Clone()
    |
    = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
 
-error: unresolved link to `cln`
-  --> $DIR/weird-syntax.rs:126:10
+error: incompatible link kind for `Clone`
+  --> $DIR/weird-syntax.rs:129:12
    |
-LL | /// The [cln][] link here is going to be unresolved, because `struct@Clone` gets
-   |          ^^^ no item named `cln` in scope
+LL | /// [cln]: struct@Clone
+   |            ^^^^^^^^^^^^ this link resolved to a trait, which is not a struct
    |
-   = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
-
-error: unresolved link to `cln`
-  --> $DIR/weird-syntax.rs:129:6
+help: to link to the trait, prefix with `trait@`
    |
-LL | /// [cln]: struct@Clone
-   |      ^^^ no item named `cln` in scope
+LL - /// [cln]: struct@Clone
+LL + /// [cln]: trait@Clone
    |
-   = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
 
 error: unresolved link to `Clone`
-  --> $DIR/weird-syntax.rs:132:9
+  --> $DIR/weird-syntax.rs:135:12
+   |
+LL | /// [cln]: Clone\(\)
+   |            ^^^^^^^^^ this link resolves to the trait `Clone`, which is not a function
+   |
+help: to link to the trait, prefix with `trait@`
    |
-LL | /// The [cln][] link here will produce a plain text suggestion
-   |         ^^^^^ this link resolves to the trait `Clone`, which is not a function
+LL - /// [cln]: Clone\(\)
+LL + /// [cln]: trait@Clone
    |
-   = help: to link to the trait, prefix with `trait@`: trait@Clone
 
 error: incompatible link kind for `Clone`
-  --> $DIR/weird-syntax.rs:137:9
+  --> $DIR/weird-syntax.rs:141:12
    |
-LL | /// The [cln][] link here will produce a plain text suggestion
-   |         ^^^^^ this link resolved to a trait, which is not a struct
+LL | /// [cln]: struct\@Clone
+   |            ^^^^^^^^^^^^^ this link resolved to a trait, which is not a struct
    |
-   = help: to link to the trait, prefix with `trait@`: trait@Clone
+help: to link to the trait, prefix with `trait@`
+   |
+LL - /// [cln]: struct\@Clone
+LL + /// [cln]: trait@struct
+   |
+
+error: incompatible link kind for `Clone`
+  --> $DIR/weird-syntax.rs:149:12
+   |
+LL | /// [cln]: struct\@Clone
+   |            ^^^^^^^^^^^^^ this link resolved to a trait, which is not a struct
+   |
+help: to link to the trait, prefix with `trait@`
+   |
+LL - /// [cln]: struct\@Clone
+LL + /// [cln]: trait@struct
+   |
+
+error: unresolved link to `the`
+  --> $DIR/weird-syntax.rs:155:56
+   |
+LL | /// - [`SDL_PROP_WINDOW_CREATE_COCOA_WINDOW_POINTER`]: the
+   |                                                        ^^^ no item named `the` in scope
+   |
+   = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
 
-error: aborting due to 26 previous errors
+error: aborting due to 27 previous errors