Fix multiline annotations in over- elems in math changing the baseline (#5459)

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

@@ -127,7 +127,9 @@ fn layout_vec_body(
     let denom_style = style_for_denominator(styles);
     let mut flat = vec![];
     for child in column {
-        flat.push(ctx.layout_into_run(child, styles.chain(&denom_style))?);
+        // We allow linebreaks in cases and vectors, which are functionally
+        // identical to commas.
+        flat.extend(ctx.layout_into_run(child, styles.chain(&denom_style))?.rows());
     }
     // We pad ascent and descent with the ascent and descent of the paren
     // to ensure that normal vectors are aligned with others unless they are

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

@@ -121,7 +121,6 @@ pub fn stack(
     alternator: LeftRightAlternator,
     minimum_ascent_descent: Option<(Abs, Abs)>,
 ) -> Frame {
-    let rows: Vec<_> = rows.into_iter().flat_map(|r| r.rows()).collect();
     let AlignmentResult { points, width } = alignments(&rows);
     let rows: Vec<_> = rows
         .into_iter()

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

@@ -297,7 +297,7 @@ fn layout_underoverspreader(
             if let Some(annotation) = annotation {
                 let under_style = style_for_subscript(styles);
                 let annotation_styles = styles.chain(&under_style);
-                rows.push(ctx.layout_into_run(annotation, annotation_styles)?);
+                rows.extend(ctx.layout_into_run(annotation, annotation_styles)?.rows());
             }
             0
         }
@@ -305,7 +305,7 @@ fn layout_underoverspreader(
             if let Some(annotation) = annotation {
                 let over_style = style_for_superscript(styles);
                 let annotation_styles = styles.chain(&over_style);
-                rows.push(ctx.layout_into_run(annotation, annotation_styles)?);
+                rows.extend(ctx.layout_into_run(annotation, annotation_styles)?.rows());
             }
             rows.push(stretched.into());
             rows.push(MathRun::new(vec![body]));

tests/suite/math/cases.typ

@@ -15,3 +15,8 @@ $ x = cases(1, 2) $
 --- math-cases-delim ---
 #set math.cases(delim: sym.angle.l)
 $ cases(a, b, c) $
+
+--- math-cases-linebreaks ---
+// Currently linebreaks are equivalent to commas, though this behaviour may
+// change in the future.
+$ cases(a, b, c) cases(reverse: #true, a \ b \ c) $

tests/suite/math/mat.typ

@@ -229,6 +229,11 @@ $ mat(delim: angle.r, 1, 2; 3, 4) $
 $ mat(delim: #(none, "["), 1, 2; 3, 4) $
 $ mat(delim: #(sym.angle.r, sym.bracket.double.r), 1, 2; 3, 4) $
 
+--- math-mat-linebreaks ---
+// Unlike cases and vectors, linebreaks are discarded in matrices. This
+// behaviour may change in the future.
+$ mat(a; b; c) mat(a \ b \ c) $
+
 --- issue-1617-mat-align ---
 #set page(width: auto)
 $ mat(a, b; c, d) mat(x; y) $

tests/suite/math/underover.typ

@@ -45,3 +45,10 @@ $A_2 != overline(A)_2 != underline(A)_2 != underline(overline(A))_2 \
 $J^b != overline(J)^b != underline(J)^b != underline(overline(J))^b \
  K^3 != overline(K)^3 != underline(K)^3 != underline(overline(K))^3 \
  T^i != overline(T)^i != underline(T)^i != underline(overline(T))^i$
+
+--- math-underover-multiline-annotation ---
+// Test that multiline annotations do not change the baseline.
+$ S = overbrace(beta (alpha) S I, "one line")
+    - overbrace(mu (N), "two" \  "line") $
+$ S = underbrace(beta (alpha) S I, "one line")
+    - underbrace(mu (N), "two" \  "line") $

tests/suite/math/vec.typ

@@ -49,3 +49,8 @@ $ vec(1, 2) $
 --- math-vec-delim-invalid-closing ---
 // Error: 22-33 invalid delimiter: "%"
 #set math.vec(delim: (none, "%"))
+
+--- math-vec-linebreaks ---
+// Currently linebreaks are equivalent to commas, though this behaviour may
+// change in the future.
+$ vec(a, b, c) vec(a \ b \ c) $