Initial fix for spacing on decorated math operators (#1023)

library/src/math/accent.rs

@@ -58,6 +58,8 @@ impl LayoutMath for AccentElem {
         let base = ctx.layout_fragment(&self.base())?;
         ctx.unstyle();
 
+        // Preserve class to preserve automatic spacing.
+        let base_class = base.class().unwrap_or(MathClass::Normal);
         let base_attach = match &base {
             MathFragment::Glyph(base) => {
                 attachment(ctx, base.id, base.italics_correction)
@@ -93,7 +95,11 @@ impl LayoutMath for AccentElem {
         frame.set_baseline(baseline);
         frame.push_frame(accent_pos, accent);
         frame.push_frame(base_pos, base.into_frame());
-        ctx.push(FrameFragment::new(ctx, frame).with_base_ascent(base_ascent));
+        ctx.push(
+            FrameFragment::new(ctx, frame)
+                .with_class(base_class)
+                .with_base_ascent(base_ascent),
+        );
 
         Ok(())
     }

library/src/math/cancel.rs

@@ -90,7 +90,10 @@ pub struct CancelElem {
 
 impl LayoutMath for CancelElem {
     fn layout_math(&self, ctx: &mut MathContext) -> SourceResult<()> {
-        let mut body = ctx.layout_frame(&self.body())?;
+        let body = ctx.layout_fragment(&self.body())?;
+        // Use the same math class as the body, in order to preserve automatic spacing around it.
+        let body_class = body.class().unwrap_or(MathClass::Special);
+        let mut body = body.into_frame();
 
         let styles = ctx.styles();
         let body_size = body.size();
@@ -130,7 +133,7 @@ impl LayoutMath for CancelElem {
             body.push_frame(center, second_line);
         }
 
-        ctx.push(FrameFragment::new(ctx, body));
+        ctx.push(FrameFragment::new(ctx, body).with_class(body_class));
 
         Ok(())
     }

library/src/math/row.rs

@@ -95,6 +95,20 @@ impl MathRow {
         self.iter().map(MathFragment::descent).max().unwrap_or_default()
     }
 
+    pub fn class(&self) -> MathClass {
+        // Predict the class of the output of 'into_fragment'
+        if self.0.len() == 1 {
+            self.0
+                .first()
+                .and_then(|fragment| fragment.class())
+                .unwrap_or(MathClass::Special)
+        } else {
+            // FrameFragment::new() (inside 'into_fragment' in this branch) defaults
+            // to MathClass::Normal for its class.
+            MathClass::Normal
+        }
+    }
+
     pub fn into_frame(self, ctx: &MathContext) -> Frame {
         let styles = ctx.styles();
         let align = AlignElem::alignment_in(styles).x.resolve(styles);

library/src/math/underover.rs

@@ -202,6 +202,7 @@ fn layout(
 ) -> SourceResult<()> {
     let gap = gap.scaled(ctx);
     let body = ctx.layout_row(body)?;
+    let body_class = body.class();
     let glyph = GlyphFragment::new(ctx, c, span);
     let stretched = glyph.stretch_horizontal(ctx, body.width(), Abs::zero());
 
@@ -226,7 +227,7 @@ fn layout(
     }
 
     let frame = stack(ctx, rows, Align::Center, gap, baseline);
-    ctx.push(FrameFragment::new(ctx, frame));
+    ctx.push(FrameFragment::new(ctx, frame).with_class(body_class));
 
     Ok(())
 }

tests/typ/math/spacing.typ

@@ -29,3 +29,12 @@ $a - b ident c quad (mod 2)$
 // Test spacing for set comprehension.
 #set page(width: auto)
 $ { x in RR | x "is natural" and x < 10 } $
+
+---
+// Test spacing for operators with decorations and modifiers on them
+#set page(width: auto)
+$a ident b + c - d => e log 5 op("ln") 6$ \
+$a cancel(ident) b overline(+) c arrow(-) d hat(=>) e cancel(log) 5 dot(op("ln")) 6$ \
+$a overbrace(ident) b underline(+) c grave(-) d underbracket(=>) e circle(log) 5 caron(op("ln")) 6$ \
+\
+$a attach(ident, tl: a, tr: b) b attach(limits(+), t: a, b: b) c tilde(-) d breve(=>) e attach(limits(log), t: a, b: b) 5 attach(op("ln"), tr: a, bl: b) 6$