Fix newline in text in math

Fixes #1948

crates/typst-library/src/math/ctx.rs

@@ -2,6 +2,7 @@ use ttf_parser::gsub::SubstitutionSubtable;
 use ttf_parser::math::MathValue;
 use typst::font::{FontStyle, FontWeight};
 use typst::model::realize;
+use typst::syntax::is_newline;
 use unicode_segmentation::UnicodeSegmentation;
 
 use super::*;
@@ -207,25 +208,50 @@ impl<'a, 'b, 'v> MathContext<'a, 'b, 'v> {
             FrameFragment::new(self, frame).into()
         } else {
             // Anything else is handled by Typst's standard text layout.
-            let spaced = text.graphemes(true).nth(1).is_some();
             let mut style = self.style;
             if self.style.italic == Smart::Auto {
                 style = style.with_italic(false);
             }
             let text: EcoString = text.chars().map(|c| style.styled_char(c)).collect();
-            let text = TextElem::packed(text)
+            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(self.layout_complex_text(piece, span)?.into());
+                    }
+                }
+                let mut frame = MathRow::new(fragments).into_frame(self);
+                let axis = scaled!(self, axis_height);
+                frame.set_baseline(frame.height() / 2.0 + axis);
+                FrameFragment::new(self, frame).into()
+            } else {
+                self.layout_complex_text(&text, span)?.into()
+            }
+        };
+        Ok(fragment)
+    }
+
+    pub fn layout_complex_text(
+        &mut self,
+        text: &str,
+        span: Span,
+    ) -> SourceResult<FrameFragment> {
+        let spaced = text.graphemes(true).nth(1).is_some();
+        let elem = TextElem::packed(text)
             .styled(TextElem::set_top_edge(TopEdge::Metric(TopEdgeMetric::Bounds)))
             .styled(TextElem::set_bottom_edge(BottomEdge::Metric(
                 BottomEdgeMetric::Bounds,
             )))
             .spanned(span);
-            let par = ParElem::new(vec![text]);
 
         // 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 = par
+        let frame = ParElem::new(vec![elem])
             .layout(
                 self.vt,
                 self.outer.chain(&self.local),
@@ -234,12 +260,10 @@ impl<'a, 'b, 'v> MathContext<'a, 'b, 'v> {
                 false,
             )?
             .into_frame();
-            FrameFragment::new(self, frame)
+
+        Ok(FrameFragment::new(self, frame)
             .with_class(MathClass::Alphabetic)
-                .with_spaced(spaced)
+            .with_spaced(spaced))
-                .into()
-        };
-        Ok(fragment)
     }
 
     pub fn styles(&self) -> StyleChain {

tests/typ/bugs/math-text-break.typ

@@ -0,0 +1,4 @@
+// Test text with linebreaks in math.
+
+---
+$ x := "a\nb\nc\nd\ne" $