Fix math spacing bugs

10 files changed, 166 insertions, 54 deletions

diff --git a/library/src/math/atom.rs b/library/src/math/atom.rs
index 5b35d289..6d7359bf 100644
--- a/library/src/math/atom.rs
+++ b/library/src/math/atom.rs
@@ -31,7 +31,7 @@ impl LayoutMath for AtomNode {
         {
             // A single letter that is available in the math font.
             if ctx.style.size == MathSize::Display
-                && glyph.class() == Some(MathClass::Large)
+                && glyph.class == Some(MathClass::Large)
             {
                 let height = scaled!(ctx, display_operator_min_height);
                 ctx.push(glyph.stretch_vertical(ctx, height, Abs::zero()));
@@ -49,7 +49,8 @@ impl LayoutMath for AtomNode {
             ctx.push(frame);
         } else {
             // Anything else is handled by Typst's standard text layout.
-            TextNode(self.0.clone()).pack().layout_math(ctx)?;
+            let frame = ctx.layout_non_math(&TextNode(self.0.clone()).pack())?;
+            ctx.push(FrameFragment::new(frame).with_class(MathClass::Alphabetic));
         }
 
         Ok(())
diff --git a/library/src/math/ctx.rs b/library/src/math/ctx.rs
index 41299f98..551d6cd7 100644
--- a/library/src/math/ctx.rs
+++ b/library/src/math/ctx.rs
@@ -30,6 +30,7 @@ pub(super) struct MathContext<'a, 'b, 'v> {
     pub ttf: &'a ttf_parser::Face<'a>,
     pub table: ttf_parser::math::Table<'a>,
     pub constants: ttf_parser::math::Constants<'a>,
+    pub space_width: Em,
     pub fill: Paint,
     pub lang: Lang,
     pub row: MathRow,
@@ -50,6 +51,14 @@ impl<'a, 'b, 'v> MathContext<'a, 'b, 'v> {
         let table = font.ttf().tables().math.unwrap();
         let constants = table.constants.unwrap();
         let size = styles.get(TextNode::SIZE);
+
+        let ttf = font.ttf();
+        let space_width = ttf
+            .glyph_index(' ')
+            .and_then(|id| ttf.glyph_hor_advance(id))
+            .map(|advance| font.to_em(advance))
+            .unwrap_or(THICK);
+
         Self {
             vt,
             outer: styles,
@@ -71,6 +80,7 @@ impl<'a, 'b, 'v> MathContext<'a, 'b, 'v> {
             ttf: font.ttf(),
             table,
             constants,
+            space_width,
             row: MathRow::new(),
             base_size: size,
             scaled_size: size,
@@ -79,7 +89,16 @@ impl<'a, 'b, 'v> MathContext<'a, 'b, 'v> {
     }
 
     pub fn push(&mut self, fragment: impl Into<MathFragment>) {
-        self.row.push(self.scaled_size, self.style, fragment);
+        self.row
+            .push(self.scaled_size, self.space_width, self.style, fragment);
+    }
+
+    pub fn extend(&mut self, row: MathRow) {
+        let mut iter = row.0.into_iter();
+        if let Some(first) = iter.next() {
+            self.push(first);
+        }
+        self.row.0.extend(iter);
     }
 
     pub fn layout_non_math(&mut self, content: &Content) -> SourceResult<Frame> {
diff --git a/library/src/math/fragment.rs b/library/src/math/fragment.rs
index d6d55cc3..fef57a0a 100644
--- a/library/src/math/fragment.rs
+++ b/library/src/math/fragment.rs
@@ -6,8 +6,9 @@ pub(super) enum MathFragment {
     Variant(VariantFragment),
     Frame(FrameFragment),
     Spacing(Abs),
-    Align,
+    Space,
     Linebreak,
+    Align,
 }
 
 impl MathFragment {
@@ -54,13 +55,26 @@ impl MathFragment {
 
     pub fn class(&self) -> Option<MathClass> {
         match self {
-            Self::Glyph(glyph) => glyph.class(),
-            Self::Variant(variant) => variant.class(),
+            Self::Glyph(glyph) => glyph.class,
+            Self::Variant(variant) => variant.class,
             Self::Frame(fragment) => Some(fragment.class),
             _ => None,
         }
     }
 
+    pub fn set_class(&mut self, class: MathClass) {
+        match self {
+            Self::Glyph(glyph) => glyph.class = Some(class),
+            Self::Variant(variant) => variant.class = Some(class),
+            Self::Frame(fragment) => fragment.class = class,
+            _ => {}
+        }
+    }
+
+    pub fn participating(&self) -> bool {
+        !matches!(self, Self::Space | Self::Spacing(_) | Self::Align)
+    }
+
     pub fn italics_correction(&self) -> Abs {
         match self {
             Self::Glyph(glyph) => glyph.italics_correction,
@@ -99,7 +113,7 @@ impl From<FrameFragment> for MathFragment {
 
 impl From<Frame> for MathFragment {
     fn from(frame: Frame) -> Self {
-        Self::Frame(FrameFragment { frame, class: MathClass::Normal, limits: false })
+        Self::Frame(FrameFragment::new(frame))
     }
 }
 
@@ -112,6 +126,7 @@ pub(super) struct GlyphFragment {
     pub ascent: Abs,
     pub descent: Abs,
     pub italics_correction: Abs,
+    pub class: Option<MathClass>,
 }
 
 impl GlyphFragment {
@@ -144,6 +159,10 @@ impl GlyphFragment {
             ascent: bbox.y_max.scaled(ctx),
             descent: -bbox.y_min.scaled(ctx),
             italics_correction: italics,
+            class: match c {
+                ':' => Some(MathClass::Relation),
+                _ => unicode_math_class::class(c),
+            },
         }
     }
 
@@ -151,16 +170,13 @@ impl GlyphFragment {
         self.ascent + self.descent
     }
 
-    pub fn class(&self) -> Option<MathClass> {
-        unicode_math_class::class(self.c)
-    }
-
     pub fn to_variant(&self, ctx: &MathContext) -> VariantFragment {
         VariantFragment {
             c: self.c,
             id: Some(self.id),
             frame: self.to_frame(ctx),
             italics_correction: self.italics_correction,
+            class: self.class,
         }
     }
 
@@ -191,12 +207,7 @@ pub struct VariantFragment {
     pub id: Option<GlyphId>,
     pub frame: Frame,
     pub italics_correction: Abs,
-}
-
-impl VariantFragment {
-    pub fn class(&self) -> Option<MathClass> {
-        unicode_math_class::class(self.c)
-    }
+    pub class: Option<MathClass>,
 }
 
 #[derive(Debug, Clone)]
@@ -204,6 +215,30 @@ pub struct FrameFragment {
     pub frame: Frame,
     pub class: MathClass,
     pub limits: bool,
+    pub spaced: bool,
+}
+
+impl FrameFragment {
+    pub fn new(frame: Frame) -> Self {
+        Self {
+            frame,
+            class: MathClass::Normal,
+            limits: false,
+            spaced: false,
+        }
+    }
+
+    pub fn with_class(self, class: MathClass) -> Self {
+        Self { class, ..self }
+    }
+
+    pub fn with_limits(self, limits: bool) -> Self {
+        Self { limits, ..self }
+    }
+
+    pub fn with_spaced(self, spaced: bool) -> Self {
+        Self { spaced, ..self }
+    }
 }
 
 /// Look up the italics correction for a glyph.
diff --git a/library/src/math/lr.rs b/library/src/math/lr.rs
index 89d12380..d5951050 100644
--- a/library/src/math/lr.rs
+++ b/library/src/math/lr.rs
@@ -69,9 +69,7 @@ impl LayoutMath for LrNode {
             }
         }
 
-        for fragment in row.0 {
-            ctx.push(fragment);
-        }
+        ctx.extend(row);
 
         Ok(())
     }
diff --git a/library/src/math/mod.rs b/library/src/math/mod.rs
index 1e7a6580..2cc8fa9e 100644
--- a/library/src/math/mod.rs
+++ b/library/src/math/mod.rs
@@ -43,6 +43,7 @@ use self::row::*;
 use self::spacing::*;
 use crate::layout::HNode;
 use crate::layout::ParNode;
+use crate::layout::Spacing;
 use crate::prelude::*;
 use crate::text::LinebreakNode;
 use crate::text::TextNode;
@@ -222,6 +223,7 @@ impl LayoutMath for FormulaNode {
 impl LayoutMath for Content {
     fn layout_math(&self, ctx: &mut MathContext) -> SourceResult<()> {
         if self.is::<SpaceNode>() {
+            ctx.push(MathFragment::Space);
             return Ok(());
         }
 
@@ -230,6 +232,17 @@ impl LayoutMath for Content {
             return Ok(());
         }
 
+        if let Some(node) = self.to::<HNode>() {
+            if let Spacing::Relative(rel) = node.amount {
+                if rel.rel.is_zero() {
+                    ctx.push(MathFragment::Spacing(
+                        rel.abs.resolve(ctx.outer.chain(&ctx.map)),
+                    ));
+                }
+            }
+            return Ok(());
+        }
+
         if let Some(node) = self.to::<SequenceNode>() {
             for child in &node.0 {
                 child.layout_math(ctx)?;
@@ -242,7 +255,7 @@ impl LayoutMath for Content {
         }
 
         let frame = ctx.layout_non_math(self)?;
-        ctx.push(frame);
+        ctx.push(FrameFragment::new(frame).with_spaced(true));
 
         Ok(())
     }
diff --git a/library/src/math/op.rs b/library/src/math/op.rs
index cf1f9105..22daee65 100644
--- a/library/src/math/op.rs
+++ b/library/src/math/op.rs
@@ -39,11 +39,11 @@ impl OpNode {
 impl LayoutMath for OpNode {
     fn layout_math(&self, ctx: &mut MathContext) -> SourceResult<()> {
         let frame = ctx.layout_non_math(&TextNode(self.text.clone()).pack())?;
-        ctx.push(FrameFragment {
-            frame,
-            class: MathClass::Large,
-            limits: self.limits,
-        });
+        ctx.push(
+            FrameFragment::new(frame)
+                .with_class(MathClass::Large)
+                .with_limits(self.limits),
+        );
         Ok(())
     }
 }
diff --git a/library/src/math/row.rs b/library/src/math/row.rs
index f7b2b384..f75aed99 100644
--- a/library/src/math/row.rs
+++ b/library/src/math/row.rs
@@ -15,36 +15,60 @@ impl MathRow {
     pub fn push(
         &mut self,
         font_size: Abs,
+        space_width: Em,
         style: MathStyle,
         fragment: impl Into<MathFragment>,
     ) {
-        let fragment = fragment.into();
-        if let Some(fragment_class) = fragment.class() {
-            for (i, prev) in self.0.iter().enumerate().rev() {
-                if matches!(prev, MathFragment::Align) {
-                    continue;
-                }
+        let mut fragment = fragment.into();
+        if !fragment.participating() {
+            self.0.push(fragment);
+            return;
+        }
 
-                let mut amount = Abs::zero();
-                if let MathFragment::Glyph(glyph) = *prev {
-                    if !glyph.italics_correction.is_zero()
-                        && fragment_class != MathClass::Alphabetic
-                    {
-                        amount += glyph.italics_correction;
-                    }
+        let mut space = false;
+        for (i, prev) in self.0.iter().enumerate().rev() {
+            if !prev.participating() {
+                space |= matches!(prev, MathFragment::Space);
+                if matches!(prev, MathFragment::Spacing(_)) {
+                    break;
                 }
+                continue;
+            }
 
-                if let Some(prev_class) = prev.class() {
-                    amount += spacing(prev_class, fragment_class, style).at(font_size);
+            if fragment.class() == Some(MathClass::Vary) {
+                if matches!(
+                    prev.class(),
+                    Some(
+                        MathClass::Normal
+                            | MathClass::Alphabetic
+                            | MathClass::Binary
+                            | MathClass::Closing
+                            | MathClass::Fence
+                            | MathClass::Relation
+                    )
+                ) {
+                    fragment.set_class(MathClass::Binary);
                 }
+            }
 
-                if !amount.is_zero() {
-                    self.0.insert(i + 1, MathFragment::Spacing(amount));
+            let mut amount = Abs::zero();
+            if let MathFragment::Glyph(glyph) = *prev {
+                if !glyph.italics_correction.is_zero()
+                    && fragment.class() != Some(MathClass::Alphabetic)
+                {
+                    amount += glyph.italics_correction;
                 }
+            }
+
+            amount += spacing(prev, &fragment, style, space, space_width).at(font_size);
 
-                break;
+            if !amount.is_zero() {
+                self.0.insert(i + 1, MathFragment::Spacing(amount));
             }
+
+            break;
         }
+
         self.0.push(fragment);
     }
 
diff --git a/library/src/math/script.rs b/library/src/math/script.rs
index 671651d9..2c765fbf 100644
--- a/library/src/math/script.rs
+++ b/library/src/math/script.rs
@@ -139,7 +139,7 @@ fn scripts(
     frame.push_frame(base_pos, base.to_frame(ctx));
     frame.push_frame(sub_pos, sub);
     frame.push_frame(sup_pos, sup);
-    ctx.push(FrameFragment { frame, class, limits: false });
+    ctx.push(FrameFragment::new(frame).with_class(class));
 
     Ok(())
 }
@@ -172,7 +172,7 @@ fn limits(
     frame.push_frame(base_pos, base.to_frame(ctx));
     frame.push_frame(sub_pos, sub);
     frame.push_frame(sup_pos, sup);
-    ctx.push(FrameFragment { frame, class, limits: false });
+    ctx.push(FrameFragment::new(frame).with_class(class));
 
     Ok(())
 }
diff --git a/library/src/math/spacing.rs b/library/src/math/spacing.rs
index cf86b698..7083c5e1 100644
--- a/library/src/math/spacing.rs
+++ b/library/src/math/spacing.rs
@@ -1,10 +1,10 @@
 use super::*;
 
-const ZERO: Em = Em::zero();
-const THIN: Em = Em::new(1.0 / 6.0);
-const MEDIUM: Em = Em::new(2.0 / 9.0);
-const THICK: Em = Em::new(5.0 / 18.0);
-const QUAD: Em = Em::new(1.0);
+pub(super) const ZERO: Em = Em::zero();
+pub(super) const THIN: Em = Em::new(1.0 / 6.0);
+pub(super) const MEDIUM: Em = Em::new(2.0 / 9.0);
+pub(super) const THICK: Em = Em::new(5.0 / 18.0);
+pub(super) const QUAD: Em = Em::new(1.0);
 
 /// Hook up all spacings.
 pub(super) fn define(math: &mut Scope) {
@@ -15,10 +15,20 @@ pub(super) fn define(math: &mut Scope) {
 }
 
 /// Determine the spacing between two fragments in a given style.
-pub(super) fn spacing(left: MathClass, right: MathClass, style: MathStyle) -> Em {
+pub(super) fn spacing(
+    left: &MathFragment,
+    right: &MathFragment,
+    style: MathStyle,
+    space: bool,
+    space_width: Em,
+) -> Em {
     use MathClass::*;
     let script = style.size <= MathSize::Script;
-    match (left, right) {
+    let (Some(l), Some(r)) = (left.class(), right.class()) else {
+        return ZERO;
+    };
+
+    match (l, r) {
         // No spacing before punctuation; thin spacing after punctuation, unless
         // in script size.
         (_, Punctuation) => ZERO,
@@ -33,12 +43,23 @@ pub(super) fn spacing(left: MathClass, right: MathClass, style: MathStyle) -> Em
         (Relation, _) | (_, Relation) if !script => THICK,
 
         // Medium spacing around binary operators, unless in script size.
-        (Vary | Binary, _) | (_, Vary | Binary) if !script => MEDIUM,
+        (Binary, _) | (_, Binary) if !script => MEDIUM,
 
         // Thin spacing around large operators, unless next to a delimiter.
         (Large, Opening | Fence) | (Closing | Fence, Large) => ZERO,
         (Large, _) | (_, Large) => THIN,
 
+        // Spacing around spaced frames.
+        _ if space && (is_spaced(left) || is_spaced(right)) => space_width,
+
         _ => ZERO,
     }
 }
+
+/// Whether this fragment should react to adjacent spaces.
+fn is_spaced(fragment: &MathFragment) -> bool {
+    match fragment {
+        MathFragment::Frame(frame) => frame.spaced,
+        _ => fragment.class() == Some(MathClass::Fence),
+    }
+}
diff --git a/library/src/math/stretch.rs b/library/src/math/stretch.rs
index bd72a769..aee226d1 100644
--- a/library/src/math/stretch.rs
+++ b/library/src/math/stretch.rs
@@ -178,6 +178,7 @@ fn assemble(
         id: None,
         frame,
         italics_correction: Abs::zero(),
+        class: base.class,
     }
 }