Update math TextElem layout to separate out SymbolElem

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

@@ -538,11 +538,7 @@ fn layout_realized(
     } else if let Some(elem) = elem.to_packed::<TextElem>() {
         self::text::layout_text(elem, ctx, styles)?;
     } else if let Some(elem) = elem.to_packed::<SymbolElem>() {
-        // This is a hack to avoid affecting layout that will be replaced in a
-        // later commit.
-        let text_elem = TextElem::new(elem.text.to_string().into());
-        let packed = Packed::new(text_elem);
-        self::text::layout_text(&packed, ctx, styles)?;
+        self::text::layout_symbol(elem, ctx, styles)?;
     } else if let Some(elem) = elem.to_packed::<BoxElem>() {
         layout_box(elem, ctx, styles)?;
     } else if elem.is::<AlignPointElem>() {

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

@@ -2,7 +2,7 @@ use std::f64::consts::SQRT_2;
 
 use ecow::{eco_vec, EcoString};
 use typst_library::diag::SourceResult;
-use typst_library::foundations::{Packed, StyleChain, StyleVec};
+use typst_library::foundations::{Packed, StyleChain, StyleVec, SymbolElem};
 use typst_library::layout::{Abs, Size};
 use typst_library::math::{EquationElem, MathSize, MathVariant};
 use typst_library::text::{
@@ -22,54 +22,66 @@ pub fn layout_text(
 ) -> SourceResult<()> {
     let text = &elem.text;
     let span = elem.span();
-    let mut chars = text.chars();
-    let math_size = EquationElem::size_in(styles);
-    let mut dtls = ctx.dtls_table.is_some();
-    let fragment: MathFragment = if let Some(mut glyph) = chars
-        .next()
-        .filter(|_| chars.next().is_none())
-        .map(|c| dtls_char(c, &mut dtls))
-        .map(|c| styled_char(styles, c, true))
-        .and_then(|c| GlyphFragment::try_new(ctx, styles, c, span))
-    {
-        // A single letter that is available in the math font.
-        if dtls {
-            glyph.make_dotless_form(ctx);
-        }
+    let fragment = if text.contains(is_newline) {
+        layout_text_lines(text.split(is_newline), span, ctx, styles)?
+    } else {
+        layout_inline_text(text, span, ctx, styles)?
+    };
+    ctx.push(fragment);
+    Ok(())
+}
 
-        match math_size {
-            MathSize::Script => {
-                glyph.make_script_size(ctx);
-            }
-            MathSize::ScriptScript => {
-                glyph.make_script_script_size(ctx);
-            }
-            _ => (),
+/// Layout multiple lines of text.
+fn layout_text_lines<'a>(
+    lines: impl Iterator<Item = &'a str>,
+    span: Span,
+    ctx: &mut MathContext,
+    styles: StyleChain,
+) -> SourceResult<FrameFragment> {
+    let mut fragments = vec![];
+    for (i, line) in lines.enumerate() {
+        if i != 0 {
+            fragments.push(MathFragment::Linebreak);
         }
+        if !line.is_empty() {
+            fragments.push(layout_inline_text(line, span, ctx, styles)?.into());
+        }
+    }
+    let mut frame = MathRun::new(fragments).into_frame(styles);
+    let axis = scaled!(ctx, styles, axis_height);
+    frame.set_baseline(frame.height() / 2.0 + axis);
+    Ok(FrameFragment::new(styles, frame))
+}
 
-        if glyph.class == MathClass::Large {
-            let mut variant = if math_size == MathSize::Display {
-                let height = scaled!(ctx, styles, display_operator_min_height)
-                    .max(SQRT_2 * glyph.height());
-                glyph.stretch_vertical(ctx, height, Abs::zero())
-            } else {
-                glyph.into_variant()
-            };
-            // TeXbook p 155. Large operators are always vertically centered on the axis.
-            variant.center_on_axis(ctx);
-            variant.into()
-        } else {
-            glyph.into()
-        }
-    } else if text.chars().all(|c| c.is_ascii_digit() || c == '.') {
-        // Numbers aren't that difficult.
+/// Layout the given text string into a [`FrameFragment`] after styling all
+/// characters for the math font (without auto-italics).
+fn layout_inline_text(
+    text: &str,
+    span: Span,
+    ctx: &mut MathContext,
+    styles: StyleChain,
+) -> SourceResult<FrameFragment> {
+    if text.chars().all(|c| c.is_ascii_digit() || c == '.') {
+        // Small optimization for numbers. Note that this lays out slightly
+        // differently to normal text and is worth re-evaluating in the future.
         let mut fragments = vec![];
-        for c in text.chars() {
-            let c = styled_char(styles, c, false);
-            fragments.push(GlyphFragment::new(ctx, styles, c, span).into());
+        let is_single = text.chars().count() == 1;
+        for unstyled_c in text.chars() {
+            let c = styled_char(styles, unstyled_c, false);
+            let mut glyph = GlyphFragment::new(ctx, styles, c, span);
+            if is_single {
+                // Duplicate what `layout_glyph` does exactly even if it's
+                // probably incorrect here.
+                match EquationElem::size_in(styles) {
+                    MathSize::Script => glyph.make_script_size(ctx),
+                    MathSize::ScriptScript => glyph.make_script_script_size(ctx),
+                    _ => {}
+                }
+            }
+            fragments.push(glyph.into());
         }
         let frame = MathRun::new(fragments).into_frame(styles);
-        FrameFragment::new(styles, frame).with_text_like(true).into()
+        Ok(FrameFragment::new(styles, frame).with_text_like(true))
     } else {
         let local = [
             TextElem::set_top_edge(TopEdge::Metric(TopEdgeMetric::Bounds)),
@@ -77,64 +89,97 @@ pub fn layout_text(
         ]
         .map(|p| p.wrap());
 
-        // Anything else is handled by Typst's standard text layout.
         let styles = styles.chain(&local);
-        let text: EcoString =
+        let styled_text: EcoString =
             text.chars().map(|c| styled_char(styles, c, false)).collect();
-        if text.contains(is_newline) {
-            let mut fragments = vec![];
-            for (i, piece) in text.split(is_newline).enumerate() {
-                if i != 0 {
-                    fragments.push(MathFragment::Linebreak);
-                }
-                if !piece.is_empty() {
-                    fragments.push(layout_complex_text(piece, ctx, span, styles)?.into());
-                }
-            }
-            let mut frame = MathRun::new(fragments).into_frame(styles);
-            let axis = scaled!(ctx, styles, axis_height);
-            frame.set_baseline(frame.height() / 2.0 + axis);
-            FrameFragment::new(styles, frame).into()
-        } else {
-            layout_complex_text(&text, ctx, span, styles)?.into()
+
+        let spaced = styled_text.graphemes(true).nth(1).is_some();
+        let elem = TextElem::packed(styled_text).spanned(span);
+
+        // There isn't a natural width for a paragraph in a math environment;
+        // because it will be placed somewhere probably not at the left margin
+        // it will overflow. So emulate an `hbox` instead and allow the
+        // paragraph to extend as far as needed.
+        let frame = (ctx.engine.routines.layout_inline)(
+            ctx.engine,
+            &StyleVec::wrap(eco_vec![elem]),
+            ctx.locator.next(&span),
+            styles,
+            false,
+            Size::splat(Abs::inf()),
+            false,
+        )?
+        .into_frame();
+
+        Ok(FrameFragment::new(styles, frame)
+            .with_class(MathClass::Alphabetic)
+            .with_text_like(true)
+            .with_spaced(spaced))
+    }
+}
+
+/// Layout a single character in the math font with the correct styling applied
+/// (includes auto-italics).
+pub fn layout_symbol(
+    elem: &Packed<SymbolElem>,
+    ctx: &mut MathContext,
+    styles: StyleChain,
+) -> SourceResult<()> {
+    // Switch dotless char to normal when we have the dtls OpenType feature.
+    // This should happen before the main styling pass.
+    let (unstyled_c, dtls) = match try_dotless(elem.text) {
+        Some(c) if ctx.dtls_table.is_some() => (c, true),
+        _ => (elem.text, false),
+    };
+    let c = styled_char(styles, unstyled_c, true);
+    let fragment = match GlyphFragment::try_new(ctx, styles, c, elem.span()) {
+        Some(glyph) => layout_glyph(glyph, dtls, ctx, styles),
+        None => {
+            // Not in the math font, fallback to normal inline text layout.
+            layout_inline_text(c.encode_utf8(&mut [0; 4]), elem.span(), ctx, styles)?
+                .into()
         }
     };
-
     ctx.push(fragment);
     Ok(())
 }
 
-/// Layout the given text string into a [`FrameFragment`].
-fn layout_complex_text(
-    text: &str,
+/// Layout a [`GlyphFragment`].
+fn layout_glyph(
+    mut glyph: GlyphFragment,
+    dtls: bool,
     ctx: &mut MathContext,
-    span: Span,
     styles: StyleChain,
-) -> SourceResult<FrameFragment> {
-    // There isn't a natural width for a paragraph in a math environment;
-    // because it will be placed somewhere probably not at the left margin
-    // it will overflow. So emulate an `hbox` instead and allow the paragraph
-    // to extend as far as needed.
-    let spaced = text.graphemes(true).nth(1).is_some();
-    let elem = TextElem::packed(text).spanned(span);
-    let frame = (ctx.engine.routines.layout_inline)(
-        ctx.engine,
-        &StyleVec::wrap(eco_vec![elem]),
-        ctx.locator.next(&span),
-        styles,
-        false,
-        Size::splat(Abs::inf()),
-        false,
-    )?
-    .into_frame();
+) -> MathFragment {
+    if dtls {
+        glyph.make_dotless_form(ctx);
+    }
+    let math_size = EquationElem::size_in(styles);
+    match math_size {
+        MathSize::Script => glyph.make_script_size(ctx),
+        MathSize::ScriptScript => glyph.make_script_script_size(ctx),
+        _ => {}
+    }
 
-    Ok(FrameFragment::new(styles, frame)
-        .with_class(MathClass::Alphabetic)
-        .with_text_like(true)
-        .with_spaced(spaced))
+    if glyph.class == MathClass::Large {
+        let mut variant = if math_size == MathSize::Display {
+            let height = scaled!(ctx, styles, display_operator_min_height)
+                .max(SQRT_2 * glyph.height());
+            glyph.stretch_vertical(ctx, height, Abs::zero())
+        } else {
+            glyph.into_variant()
+        };
+        // TeXbook p 155. Large operators are always vertically centered on the
+        // axis.
+        variant.center_on_axis(ctx);
+        variant.into()
+    } else {
+        glyph.into()
+    }
 }
 
-/// Select the correct styled math letter.
+/// Style the character by selecting the unicode codepoint for italic, bold,
+/// caligraphic, etc.
 ///
 /// <https://www.w3.org/TR/mathml-core/#new-text-transform-mappings>
 /// <https://en.wikipedia.org/wiki/Mathematical_Alphanumeric_Symbols>
@@ -353,15 +398,12 @@ fn greek_exception(
     })
 }
 
-/// Switch dotless character to non dotless character for use of the dtls
-/// OpenType feature.
-pub fn dtls_char(c: char, dtls: &mut bool) -> char {
-    match (c, *dtls) {
-        ('ı', true) => 'i',
-        ('ȷ', true) => 'j',
-        _ => {
-            *dtls = false;
-            c
-        }
+/// The non-dotless version of a dotless character that can be used with the
+/// `dtls` OpenType feature.
+pub fn try_dotless(c: char) -> Option<char> {
+    match c {
+        'ı' => Some('i'),
+        'ȷ' => Some('j'),
+        _ => None,
     }
 }

tests/suite/foundations/content.typ

@@ -85,7 +85,7 @@
   [With ]
   vars
     .pairs()
-    .map(((name, value)) => $name = value$)
+    .map(((name, value)) => $#symbol(name) = value$)
     .join(", ", last: " and ")
   [ we have:]
   $ equation = result $

tests/suite/math/alignment.typ

@@ -4,10 +4,10 @@
 // Test alignment step functions.
 #set page(width: 225pt)
 $
-"a" &= c \
-&= c + 1 & "By definition" \
-&= d + 100 + 1000 \
-&= x && "Even longer" \
+a &= c \
+  &= c + 1 & "By definition" \
+  &= d + 100 + 1000 \
+  &= x && "Even longer" \
 $
 
 --- math-align-post-fix ---

tests/suite/math/delimited.typ

@@ -41,8 +41,8 @@ $floor(x/2), ceil(x/2), abs(x), norm(x)$
 --- math-lr-color ---
 // Test colored delimiters
 $ lr(
-    text("(", fill: #green) a/b
-    text(")", fill: #blue)
+    text(\(, fill: #green) a/b
+    text(\), fill: #blue)
   ) $
 
 --- math-lr-mid ---

tests/suite/math/stretch.typ

@@ -63,8 +63,8 @@ $ ext(bar.v) quad ext(bar.v.double) quad
 // Test stretch when base is given with shorthand.
 $stretch(||, size: #2em)$
 $stretch(\(, size: #2em)$
-$stretch("⟧", size: #2em)$
-$stretch("|", size: #2em)$
+$stretch(⟧, size: #2em)$
+$stretch(|, size: #2em)$
 $stretch(->, size: #2em)$
 $stretch(↣, size: #2em)$
 
@@ -87,7 +87,7 @@ $ body^"text" $
 #{
   let body = $stretch(=)$
   for i in range(24) {
-    body = $body$    
+    body = $body$
   }
   $body^"long text"$
 }