Resolve spacing before comparing (#2235)

crates/typst-library/src/layout/spacing.rs

@@ -1,5 +1,3 @@
-use std::cmp::Ordering;
-
 use crate::prelude::*;
 
 /// Inserts horizontal spacing into a paragraph.
@@ -64,9 +62,19 @@ impl Behave for HElem {
         }
     }
 
-    fn larger(&self, prev: &Content) -> bool {
-        let Some(prev) = prev.to::<Self>() else { return false };
-        self.amount() > prev.amount()
+    fn larger(
+        &self,
+        prev: &(Content, Behaviour, StyleChain),
+        styles: StyleChain,
+    ) -> bool {
+        let Some(other) = prev.0.to::<Self>() else { return false };
+        match (self.amount(), other.amount()) {
+            (Spacing::Fr(this), Spacing::Fr(other)) => this > other,
+            (Spacing::Rel(this), Spacing::Rel(other)) => {
+                this.resolve(styles) > other.resolve(prev.2)
+            }
+            _ => false,
+        }
     }
 }
 
@@ -156,9 +164,19 @@ impl Behave for VElem {
         }
     }
 
-    fn larger(&self, prev: &Content) -> bool {
-        let Some(prev) = prev.to::<Self>() else { return false };
-        self.amount() > prev.amount()
+    fn larger(
+        &self,
+        prev: &(Content, Behaviour, StyleChain),
+        styles: StyleChain,
+    ) -> bool {
+        let Some(other) = prev.0.to::<Self>() else { return false };
+        match (self.amount(), other.amount()) {
+            (Spacing::Fr(this), Spacing::Fr(other)) => this > other,
+            (Spacing::Rel(this), Spacing::Rel(other)) => {
+                this.resolve(styles) > other.resolve(prev.2)
+            }
+            _ => false,
+        }
     }
 }
 
@@ -216,16 +234,6 @@ impl From<Fr> for Spacing {
     }
 }
 
-impl PartialOrd for Spacing {
-    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
-        match (self, other) {
-            (Self::Rel(a), Self::Rel(b)) => a.partial_cmp(b),
-            (Self::Fr(a), Self::Fr(b)) => a.partial_cmp(b),
-            _ => None,
-        }
-    }
-}
-
 cast! {
     Spacing,
     self => match self {

crates/typst-library/src/shared/behave.rs

@@ -53,7 +53,7 @@ impl<'a> BehavedBuilder<'a> {
                     let i = self.staged.iter().position(|prev| {
                         let Behaviour::Weak(prev_level) = prev.1 else { return false };
                         level < prev_level
-                            || (level == prev_level && item.larger(&prev.0))
+                            || (level == prev_level && item.larger(prev, styles))
                     });
                     let Some(i) = i else { return };
                     self.staged.remove(i);

crates/typst/src/model/realize.rs

@@ -198,7 +198,11 @@ pub trait Behave {
     /// Whether this weak element is larger than a previous one and thus picked
     /// as the maximum when the levels are the same.
     #[allow(unused_variables)]
-    fn larger(&self, prev: &Content) -> bool {
+    fn larger(
+        &self,
+        prev: &(Content, Behaviour, StyleChain),
+        styles: StyleChain,
+    ) -> bool {
         false
     }
 }

tests/typ/layout/spacing.typ

@@ -24,6 +24,16 @@ A #h(0pt) B #h(0pt) \
 A B \
 A #h(-1fr) B
 
+---
+// Test spacing collapsing with different font sizes.
+#grid(columns: 2)[
+  #text(size: 12pt, block(below: 1em)[A])
+  #text(size: 8pt, block(above: 1em)[B])
+][
+  #text(size: 12pt, block(below: 1em)[A])
+  #text(size: 8pt, block(above: 1.25em)[B])
+]
+
 ---
 // Test RTL spacing.
 #set text(dir: rtl)