Do not force math.mid elements to have the Large math class (#5980)

crates/typst-layout/src/math/lr.rs

@@ -45,12 +45,12 @@ pub fn layout_lr(
 
     // Scale up fragments at both ends.
     match inner_fragments {
-        [one] => scale(ctx, one, relative_to, height, None),
+        [one] => scale_if_delimiter(ctx, one, relative_to, height, None),
         [first, .., last] => {
-            scale(ctx, first, relative_to, height, Some(MathClass::Opening));
-            scale(ctx, last, relative_to, height, Some(MathClass::Closing));
+            scale_if_delimiter(ctx, first, relative_to, height, Some(MathClass::Opening));
+            scale_if_delimiter(ctx, last, relative_to, height, Some(MathClass::Closing));
         }
-        _ => {}
+        [] => {}
     }
 
     // Handle MathFragment::Glyph fragments that should be scaled up.
@@ -58,7 +58,7 @@ pub fn layout_lr(
         if let MathFragment::Glyph(ref mut glyph) = fragment {
             if glyph.mid_stretched == Some(false) {
                 glyph.mid_stretched = Some(true);
-                scale(ctx, fragment, relative_to, height, Some(MathClass::Large));
+                scale(ctx, fragment, relative_to, height);
             }
         }
     }
@@ -97,7 +97,7 @@ pub fn layout_mid(
     for fragment in &mut fragments {
         if let MathFragment::Glyph(ref mut glyph) = fragment {
             glyph.mid_stretched = Some(false);
-            glyph.class = MathClass::Fence;
+            glyph.class = MathClass::Relation;
         }
     }
 
@@ -105,8 +105,12 @@ pub fn layout_mid(
     Ok(())
 }
 
-/// Scale a math fragment to a height.
-fn scale(
+/// Scales a math fragment to a height if it has the class Opening, Closing, or
+/// Fence.
+///
+/// In case `apply` is `Some(class)`, `class` will be applied to the fragment if
+/// it is a delimiter, in a way that cannot be overridden by the user.
+fn scale_if_delimiter(
     ctx: &mut MathContext,
     fragment: &mut MathFragment,
     relative_to: Abs,
@@ -117,20 +121,23 @@ fn scale(
         fragment.class(),
         MathClass::Opening | MathClass::Closing | MathClass::Fence
     ) {
-        // This unwrap doesn't really matter. If it is None, then the fragment
-        // won't be stretchable anyways.
-        let short_fall = DELIM_SHORT_FALL.at(fragment.font_size().unwrap_or_default());
-        stretch_fragment(
-            ctx,
-            fragment,
-            Some(Axis::Y),
-            Some(relative_to),
-            height,
-            short_fall,
-        );
+        scale(ctx, fragment, relative_to, height);
 
         if let Some(class) = apply {
             fragment.set_class(class);
         }
     }
 }
+
+/// Scales a math fragment to a height.
+fn scale(
+    ctx: &mut MathContext,
+    fragment: &mut MathFragment,
+    relative_to: Abs,
+    height: Rel<Abs>,
+) {
+    // This unwrap doesn't really matter. If it is None, then the fragment
+    // won't be stretchable anyways.
+    let short_fall = DELIM_SHORT_FALL.at(fragment.font_size().unwrap_or_default());
+    stretch_fragment(ctx, fragment, Some(Axis::Y), Some(relative_to), height, short_fall);
+}

tests/suite/math/delimited.typ

@@ -77,6 +77,14 @@ $ lr(body) quad
   lr(size: #1em, body) quad
   lr(size: #(1em+20%), body) $
 
+--- math-lr-mid-class ---
+// Test that `mid` creates a Relation, but that can be overridden.
+$ (a | b) $
+$ (a mid(|) b) $
+$ (a class("unary", |) b) $
+$ (a class("unary", mid(|)) b) $
+$ (a mid(class("unary", |)) b) $
+
 --- math-lr-unbalanced ---
 // Test unbalanced delimiters.
 $ 1/(2 (x) $