Fix italic function in math (#3651)

crates/typst/src/math/ctx.rs

@@ -11,7 +11,7 @@ use unicode_segmentation::UnicodeSegmentation;
 
 use crate::diag::SourceResult;
 use crate::engine::Engine;
-use crate::foundations::{Content, Packed, Smart, StyleChain};
+use crate::foundations::{Content, Packed, StyleChain};
 use crate::layout::{Abs, Axes, BoxElem, Em, Frame, LayoutMultiple, Regions, Size};
 use crate::math::{
     scaled_font_size, styled_char, EquationElem, FrameFragment, GlyphFragment,
@@ -202,7 +202,7 @@ impl<'a, 'b, 'v> MathContext<'a, 'b, 'v> {
         let fragment = if let Some(mut glyph) = chars
             .next()
             .filter(|_| chars.next().is_none())
-            .map(|c| styled_char(styles, c))
+            .map(|c| styled_char(styles, c, true))
             .and_then(|c| GlyphFragment::try_new(self, styles, c, span))
         {
             // A single letter that is available in the math font.
@@ -234,7 +234,7 @@ impl<'a, 'b, 'v> MathContext<'a, 'b, 'v> {
             // Numbers aren't that difficult.
             let mut fragments = vec![];
             for c in text.chars() {
-                let c = styled_char(styles, c);
+                let c = styled_char(styles, c, false);
                 fragments.push(GlyphFragment::new(self, styles, c, span).into());
             }
             let frame = MathRun::new(fragments).into_frame(self, styles);
@@ -244,13 +244,13 @@ impl<'a, 'b, 'v> MathContext<'a, 'b, 'v> {
                 TextElem::set_top_edge(TopEdge::Metric(TopEdgeMetric::Bounds)),
                 TextElem::set_bottom_edge(BottomEdge::Metric(BottomEdgeMetric::Bounds)),
                 TextElem::set_size(TextSize(scaled_font_size(self, styles).into())),
-                EquationElem::set_italic(Smart::Custom(false)),
             ]
             .map(|p| p.wrap());
 
             // Anything else is handled by Typst's standard text layout.
             let styles = styles.chain(&local);
-            let text: EcoString = text.chars().map(|c| styled_char(styles, c)).collect();
+            let 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() {

crates/typst/src/math/fragment.rs

@@ -9,7 +9,7 @@ use crate::foundations::StyleChain;
 use crate::introspection::{Meta, MetaElem};
 use crate::layout::{Abs, Corner, Em, Frame, FrameItem, Point, Size};
 use crate::math::{
-    scaled_font_size, styled_char, EquationElem, Limits, MathContext, MathSize, Scaled,
+    scaled_font_size, EquationElem, Limits, MathContext, MathSize, Scaled,
 };
 use crate::syntax::Span;
 use crate::text::{Font, Glyph, Lang, TextElem, TextItem};
@@ -234,7 +234,6 @@ impl GlyphFragment {
         c: char,
         span: Span,
     ) -> Option<Self> {
-        let c = styled_char(styles, c);
         let id = ctx.ttf.glyph_index(c)?;
         let id = Self::adjust_glyph_index(ctx, id);
         Some(Self::with_id(ctx, styles, c, id, span))

crates/typst/src/math/style.rs

@@ -289,16 +289,19 @@ pub fn style_for_denominator(styles: StyleChain) -> [LazyHash<Style>; 2] {
 ///
 /// <https://www.w3.org/TR/mathml-core/#new-text-transform-mappings>
 /// <https://en.wikipedia.org/wiki/Mathematical_Alphanumeric_Symbols>
-pub fn styled_char(styles: StyleChain, c: char) -> char {
+pub fn styled_char(styles: StyleChain, c: char, auto_italic: bool) -> char {
     use MathVariant::*;
 
     let variant = EquationElem::variant_in(styles);
     let bold = EquationElem::bold_in(styles);
-    let italic = EquationElem::italic_in(styles).unwrap_or(matches!(
-        c,
-        'a'..='z' | 'ı' | 'ȷ' | 'A'..='Z' | 'α'..='ω' |
-        '∂' | 'ϵ' | 'ϑ' | 'ϰ' | 'ϕ' | 'ϱ' | 'ϖ'
-    ));
+    let italic = EquationElem::italic_in(styles).unwrap_or(
+        auto_italic
+            && matches!(
+                c,
+                'a'..='z' | 'ı' | 'ȷ' | 'A'..='Z' | 'α'..='ω' |
+                '∂' | 'ϵ' | 'ϑ' | 'ϰ' | 'ϕ' | 'ϱ' | 'ϖ'
+            ),
+    );
 
     if let Some(c) = basic_exception(c) {
         return c;

tests/typ/bugs/3650-italic-equation.typ

@@ -0,0 +1,4 @@
+_abc $sin(x) "abc"$_ \
+$italic(sin(x) "abc" #box[abc])$ \
+*abc $sin(x) "abc"$* \
+$bold(sin(x) "abc" #box[abc])$ \