Fix backlinks (#4409)

crates/typst-ide/src/jump.rs

@@ -168,6 +168,15 @@ fn is_in_rect(pos: Point, size: Size, click: Point) -> bool {
 
 #[cfg(test)]
 mod tests {
+    //! This can be used in a normal test to determine positions:
+    //! ```
+    //! #set page(background: place(
+    //!   dx: 10pt,
+    //!   dy: 10pt,
+    //!   square(size: 2pt, fill: red),
+    //! ))
+    //! ```
+
     use std::num::NonZeroUsize;
 
     use typst::layout::{Abs, Point, Position};
@@ -200,7 +209,16 @@ mod tests {
     fn test_click(text: &str, click: Point, expected: Option<Jump>) {
         let world = TestWorld::new(text);
         let doc = typst::compile(&world).output.unwrap();
-        assert_eq!(jump_from_click(&world, &doc, &doc.pages[0].frame, click), expected);
+        let jump = jump_from_click(&world, &doc, &doc.pages[0].frame, click);
+        if let (Some(Jump::Position(pos)), Some(Jump::Position(expected))) =
+            (&jump, &expected)
+        {
+            assert_eq!(pos.page, expected.page);
+            assert_approx_eq!(pos.point.x, expected.point.x);
+            assert_approx_eq!(pos.point.y, expected.point.y);
+        } else {
+            assert_eq!(jump, expected);
+        }
     }
 
     #[track_caller]
@@ -240,4 +258,10 @@ mod tests {
         test_cursor(s, 12, None);
         test_cursor(s, 14, pos(1, 37.55, 16.58));
     }
+
+    #[test]
+    fn test_backlink() {
+        let s = "#footnote[Hi]";
+        test_click(s, point(10.0, 10.0), pos(1, 18.5, 37.1).map(Jump::Position));
+    }
 }

crates/typst/src/foundations/content.rs

@@ -137,20 +137,26 @@ impl Content {
         self.inner.label
     }
 
-    /// Set the label of the content.
+    /// Attach a label to the content.
     pub fn labelled(mut self, label: Label) -> Self {
-        self.make_mut().label = Some(label);
+        self.set_label(label);
         self
     }
 
-    /// Check whether a show rule recipe is disabled.
-    pub fn is_guarded(&self, index: RecipeIndex) -> bool {
-        self.inner.lifecycle.contains(index.0)
+    /// Set the label of the content.
+    pub fn set_label(&mut self, label: Label) {
+        self.make_mut().label = Some(label);
     }
 
-    /// Whether this content has already been prepared.
-    pub fn is_prepared(&self) -> bool {
-        self.inner.lifecycle.contains(0)
+    /// Assigns a location to the content.
+    ///
+    /// This identifies the content and e.g. makes it linkable by
+    /// `.linked(Destination::Location(loc))`.
+    ///
+    /// Useful in combination with [`Location::variant`].
+    pub fn located(mut self, loc: Location) -> Self {
+        self.set_location(loc);
+        self
     }
 
     /// Set the location of the content.
@@ -158,12 +164,22 @@ impl Content {
         self.make_mut().location = Some(location);
     }
 
+    /// Check whether a show rule recipe is disabled.
+    pub fn is_guarded(&self, index: RecipeIndex) -> bool {
+        self.inner.lifecycle.contains(index.0)
+    }
+
     /// Disable a show rule recipe.
     pub fn guarded(mut self, index: RecipeIndex) -> Self {
         self.make_mut().lifecycle.insert(index.0);
         self
     }
 
+    /// Whether this content has already been prepared.
+    pub fn is_prepared(&self) -> bool {
+        self.inner.lifecycle.contains(0)
+    }
+
     /// Mark this content as prepared.
     pub fn mark_prepared(&mut self) {
         self.make_mut().lifecycle.insert(0);
@@ -488,15 +504,6 @@ impl Content {
         self.styled(LinkElem::set_dests(smallvec![dest]))
     }
 
-    /// Make the content linkable by `.linked(Destination::Location(loc))`.
-    ///
-    /// Should be used in combination with [`Location::variant`].
-    pub fn backlinked(self, loc: Location) -> Self {
-        let mut backlink = Content::empty().spanned(self.span());
-        backlink.set_location(loc);
-        self
-    }
-
     /// Set alignments for this content.
     pub fn aligned(self, align: Alignment) -> Self {
         self.styled(AlignElem::set_alignment(align))

crates/typst/src/model/bibliography.rs

@@ -833,13 +833,16 @@ impl<'a> Generator<'a> {
                     let dest = Destination::Location(*location);
                     content = content.linked(dest);
                 }
-                content.backlinked(backlink)
+                content
             });
 
             // Render the main reference content.
-            let reference = renderer
-                .display_elem_children(&item.content, &mut prefix)
-                .backlinked(backlink);
+            let mut reference =
+                renderer.display_elem_children(&item.content, &mut prefix);
+
+            // Attach a backlink to either the prefix or the reference so that
+            // we can link to the bibliography entry.
+            prefix.as_mut().unwrap_or(&mut reference).set_location(backlink);
 
             output.push((prefix, reference));
         }

crates/typst/src/model/footnote.rs

@@ -286,7 +286,8 @@ impl Show for Packed<FootnoteEntry> {
             .pack()
             .spanned(span)
             .linked(Destination::Location(loc))
-            .backlinked(loc.variant(1));
+            .located(loc.variant(1));
+
         Ok(Content::sequence([
             HElem::new(self.indent(styles).into()).pack(),
             sup,

crates/typst/src/realize/mod.rs

@@ -119,6 +119,8 @@ impl<'a, 'v, 't> Builder<'a, 'v, 't> {
                 .store(EquationElem::new(content.clone()).pack().spanned(content.span()));
         }
 
+        // Styled elements and sequences can (at least currently) also have
+        // labels, so this needs to happen before they are handled.
         if let Some(realized) = process(self.engine, &mut self.locator, content, styles)?
         {
             self.engine.route.increase();

crates/typst/src/realize/process.rs

@@ -168,6 +168,7 @@ fn verdict<'a>(
         && map.is_empty()
         && (prepared || {
             target.label().is_none()
+                && target.location().is_none()
                 && !target.can::<dyn ShowSet>()
                 && !target.can::<dyn Locatable>()
                 && !target.can::<dyn Synthesize>()