Fix backslashes and line breaks in footnote lint

Author: notriddle

src/librustdoc/passes/lint/footnotes.rs

@@ -23,13 +23,11 @@ pub(crate) fn visit_item(cx: &DocContext<'_>, item: &Item, hir_id: HirId, dox: &
         match event {
             Event::Text(text)
                 if &*text == "["
-                    && let Some((Event::Text(text), _)) = parser.peek()
-                    && text.trim_start().starts_with('^')
-                    && parser.next().is_some()
-                    && let Some((Event::Text(text), end_span)) = parser.peek()
-                    && &**text == "]" =>
+                    && (span.start == 0 || dox.as_bytes().get(span.start - 1) != Some(&b'\\'))
+                    && let Some(len) = scan_footnote_ref(&dox[span.start..]) =>
             {
-                missing_footnote_references.insert(Range { start: span.start, end: end_span.end });
+                missing_footnote_references
+                    .insert(Range { start: span.start, end: span.start + len });
             }
             Event::FootnoteReference(label) => {
                 footnote_references.insert(label);
@@ -85,3 +83,35 @@ pub(crate) fn visit_item(cx: &DocContext<'_>, item: &Item, hir_id: HirId, dox: &
         );
     }
 }
+
+fn scan_footnote_ref(dox: &str) -> Option<usize> {
+    let dox = dox.as_bytes();
+    let mut i = 0;
+    if dox.get(i) != Some(&b'[') {
+        return None;
+    }
+    i += 1;
+    if dox.get(i) != Some(&b'^') {
+        return None;
+    }
+    i += 1;
+    while let Some(&c) = dox.get(i) {
+        if c == b']' {
+            i += 1;
+            return Some(i);
+        }
+        if c == b'\r' || c == b'\n' || c == b'[' {
+            // Can't nest things like this.
+            break;
+        }
+        if c == b'\\' {
+            i += 1;
+        }
+        if dox.get(i) == Some(&b'\r') || dox.get(i) == Some(&b'\n') {
+            // Can't have line breaks in footnote refs
+            break;
+        }
+        i += 1;
+    }
+    None
+}

tests/rustdoc-ui/lints/broken-footnote.rs

@@ -14,3 +14,31 @@
 //! [^1]: bar
 //!
 //! ```
+
+// Edge cases from https://pulldown-cmark.github.io/pulldown-cmark/specs/footnotes.html
+/// The following are not footnote references:
+///
+/// \[^a]
+///
+/// [\^b]
+///
+/// [^c\]
+///
+/// [^d
+/// e]
+///
+/// [^f\
+/// g]
+pub struct NotReferences;
+
+/// The following are not footnote references:
+///
+/// [^a b]
+//~^ ERROR: no footnote definition matching this footnote
+///
+/// [^1\.2]
+//~^ ERROR: no footnote definition matching this footnote
+///
+/// [^*]
+//~^ ERROR: no footnote definition matching this footnote
+pub struct EdgeCases;

tests/rustdoc-ui/lints/broken-footnote.stderr

@@ -20,5 +20,29 @@ LL | //! Footnote referenced [^1]. And [^2]. And [^bla].
    |                                   |
    |                                   help: if it should not be a footnote, escape it: `\`
 
-error: aborting due to 2 previous errors
+error: no footnote definition matching this footnote
+  --> $DIR/broken-footnote.rs:39:5
+   |
+LL | /// [^1\.2]
+   |     -^^^^^^
+   |     |
+   |     help: if it should not be a footnote, escape it: `\`
+
+error: no footnote definition matching this footnote
+  --> $DIR/broken-footnote.rs:42:5
+   |
+LL | /// [^*]
+   |     -^^^
+   |     |
+   |     help: if it should not be a footnote, escape it: `\`
+
+error: no footnote definition matching this footnote
+  --> $DIR/broken-footnote.rs:36:5
+   |
+LL | /// [^a b]
+   |     -^^^^^
+   |     |
+   |     help: if it should not be a footnote, escape it: `\`
+
+error: aborting due to 5 previous errors