Avoid spaces around ignorant and invisible elements in math (#4348)

crates/typst/src/math/fragment.rs

@@ -71,6 +71,13 @@ impl MathFragment {
         }
     }
 
+    pub fn is_ignorant(&self) -> bool {
+        match self {
+            Self::Frame(fragment) => fragment.ignorant,
+            _ => false,
+        }
+    }
+
     pub fn class(&self) -> MathClass {
         match self {
             Self::Glyph(glyph) => glyph.class,
@@ -441,6 +448,7 @@ pub struct FrameFragment {
     pub italics_correction: Abs,
     pub accent_attach: Abs,
     pub text_like: bool,
+    pub ignorant: bool,
 }
 
 impl FrameFragment {
@@ -459,6 +467,7 @@ impl FrameFragment {
             italics_correction: Abs::zero(),
             accent_attach,
             text_like: false,
+            ignorant: false,
         }
     }
 
@@ -489,6 +498,10 @@ impl FrameFragment {
     pub fn with_text_like(self, text_like: bool) -> Self {
         Self { text_like, ..self }
     }
+
+    pub fn with_ignorant(self, ignorant: bool) -> Self {
+        Self { ignorant, ..self }
+    }
 }
 
 #[derive(Debug, Clone)]

crates/typst/src/math/mod.rs

@@ -49,6 +49,7 @@ use crate::foundations::{
 };
 use crate::introspection::TagElem;
 use crate::layout::{BoxElem, Frame, FrameItem, HElem, Point, Size, Spacing, VAlignment};
+use crate::realize::Behaviour;
 use crate::realize::{process, BehavedBuilder};
 use crate::text::{LinebreakElem, SpaceElem, TextElem};
 
@@ -299,7 +300,7 @@ impl LayoutMath for Content {
         if let Some(elem) = self.to_packed::<TagElem>() {
             let mut frame = Frame::soft(Size::zero());
             frame.push(Point::zero(), FrameItem::Tag(elem.tag.clone()));
-            ctx.push(FrameFragment::new(ctx, styles, frame));
+            ctx.push(FrameFragment::new(ctx, styles, frame).with_ignorant(true));
             return Ok(());
         }
 
@@ -312,7 +313,15 @@ impl LayoutMath for Content {
             let axis = scaled!(ctx, styles, axis_height);
             frame.set_baseline(frame.height() / 2.0 + axis);
         }
-        ctx.push(FrameFragment::new(ctx, styles, frame).with_spaced(true));
+
+        ctx.push(
+            FrameFragment::new(ctx, styles, frame)
+                .with_spaced(true)
+                .with_ignorant(matches!(
+                    self.behaviour(),
+                    Behaviour::Invisible | Behaviour::Ignorant
+                )),
+        );
 
         Ok(())
     }

crates/typst/src/math/row.rs

@@ -77,14 +77,17 @@ impl MathRun {
                 fragment.set_class(MathClass::Binary);
             }
 
-            // Insert spacing between the last and this item.
+            // Insert spacing between the last and this non-ignorant item.
-            if let Some(i) = last {
+            if !fragment.is_ignorant() {
-                if let Some(s) = spacing(&resolved[i], space.take(), &fragment) {
+                if let Some(i) = last {
-                    resolved.insert(i + 1, s);
+                    if let Some(s) = spacing(&resolved[i], space.take(), &fragment) {
+                        resolved.insert(i + 1, s);
+                    }
                 }
+
+                last = Some(resolved.len());
             }
 
-            last = Some(resolved.len());
             resolved.push(fragment);
         }
 

tests/suite/math/spacing.typ

@@ -49,6 +49,16 @@ $integral f(x) thin dif x$,
 // Both are weak, collide
 $integral f(x) #h(0.166em, weak: true)dif x$
 
+--- math-spacing-ignorant ---
+// Test spacing with ignorant elements
+$#metadata(none) "text"$ \
+$#place(dx: 5em)[Placed] "text"$ \
+// Operator spacing
+$#counter("test").update(3) + b$ \
+$#place(dx: 5em)[a] + b$
+// Validate that ignorant elements are layouted
+#context test(counter("test").get(), (3,))
+
 --- issue-1052-math-number-spacing ---
 // Test spacing after numbers in math.
 $