Fix math.stretch not working vertically with attachments (#5069)

crates/typst/src/math/stretch.rs

@@ -73,9 +73,15 @@ pub(super) fn stretch_fragment(
         _ => return,
     };
 
-    let Some(axis) = axis.or_else(|| stretch_axis(ctx, &glyph)) else {
+    // Return if we attempt to stretch along an axis which isn't stretchable,
+    // so that the original fragment isn't modified.
+    let Some(stretch_axis) = stretch_axis(ctx, &glyph) else {
         return;
     };
+    let axis = axis.unwrap_or(stretch_axis);
+    if axis != stretch_axis {
+        return;
+    }
 
     let relative_to_size = relative_to.unwrap_or_else(|| fragment.size().get(axis));
 

tests/suite/math/stretch.typ

@@ -13,8 +13,8 @@ $ H stretch(=)^"define" U + p V \
   f : X stretch(arrow.hook, size: #150%)_"injective" Y \
   V stretch(->, size: #(100% + 1.5em))^("surjection") ZZ $
 
---- math-stretch-attach ---
+--- math-stretch-horizontal-attach ---
-// Test stretch interactions with attachments.
+// Test horizontal stretch interactions with attachments.
 #set page(width: auto)
 
 $stretch(stretch(=, size: #4em))_A$
@@ -28,6 +28,13 @@ $ P = Q
   U stretch(equiv)^(forall i)_"Chern-Weil" V
     stretch(equiv, size: #(120% + 2mm))^(forall i)_"Chern-Weil" W $
 
+--- math-stretch-vertical-attach ---
+// Test vertical stretch interactions with attachments.
+$arrow.t$
+$stretch(arrow.t)^"map"$
+$stretch(arrow.t, size: #2em)^"map"$
+$stretch(arrow.t, size: #200%)^"map"$
+
 --- math-stretch-horizontal ---
 // Test stretching along horizontal axis.
 #let ext(sym) = math.stretch(sym, size: 2em)