Align corner brackets to the top and bottom when scaling (#4200)

crates/typst/src/layout/align.rs

@@ -416,6 +416,16 @@ impl VAlignment {
             Self::Bottom => Self::Top,
         }
     }
+
+    /// Returns the position of this alignment in a container with the given
+    /// extent.
+    pub fn position(self, extent: Abs) -> Abs {
+        match self {
+            Self::Top => Abs::zero(),
+            Self::Horizon => extent / 2.0,
+            Self::Bottom => extent,
+        }
+    }
 }
 
 impl FixAlignment for VAlignment {

crates/typst/src/math/fragment.rs

@@ -6,7 +6,9 @@ use ttf_parser::{GlyphId, Rect};
 use unicode_math_class::MathClass;
 
 use crate::foundations::StyleChain;
-use crate::layout::{Abs, Corner, Em, Frame, FrameItem, HideElem, Point, Size};
+use crate::layout::{
+    Abs, Corner, Em, Frame, FrameItem, HideElem, Point, Size, VAlignment,
+};
 use crate::math::{
     scaled_font_size, EquationElem, Limits, MathContext, MathSize, Scaled,
 };
@@ -408,9 +410,15 @@ impl VariantFragment {
     /// Vertically adjust the fragment's frame so that it is centered
     /// on the axis.
     pub fn center_on_axis(&mut self, ctx: &MathContext) {
+        self.align_on_axis(ctx, VAlignment::Horizon)
+    }
+
+    /// Vertically adjust the fragment's frame so that it is aligned
+    /// to the given alignment on the axis.
+    pub fn align_on_axis(&mut self, ctx: &MathContext, align: VAlignment) {
         let h = self.frame.height();
         let axis = ctx.constants.axis_height().scaled(ctx, self.font_size);
-        self.frame.set_baseline(h / 2.0 + axis);
+        self.frame.set_baseline(align.inv().position(h + axis * 2.0));
     }
 }
 

crates/typst/src/math/lr.rs

@@ -10,6 +10,8 @@ use crate::math::{
 };
 use crate::text::TextElem;
 
+use super::delimiter_alignment;
+
 /// How much less high scaled delimiters can be than what they wrap.
 pub(super) const DELIM_SHORT_FALL: Em = Em::new(0.1);
 
@@ -160,7 +162,7 @@ fn scale(
 
         let short_fall = DELIM_SHORT_FALL.at(glyph.font_size);
         let mut stretched = glyph.stretch_vertical(ctx, height, short_fall);
-        stretched.center_on_axis(ctx);
+        stretched.align_on_axis(ctx, delimiter_alignment(stretched.c));
 
         *fragment = MathFragment::Variant(stretched);
         if let Some(class) = apply {

crates/typst/src/math/matrix.rs

@@ -20,6 +20,8 @@ use crate::text::TextElem;
 use crate::utils::Numeric;
 use crate::visualize::{FixedStroke, Geometry, LineCap, Shape, Stroke};
 
+use super::delimiter_alignment;
+
 const DEFAULT_ROW_GAP: Em = Em::new(0.5);
 const DEFAULT_COL_GAP: Em = Em::new(0.5);
 const VERTICAL_PADDING: Ratio = Ratio::new(0.1);
@@ -610,7 +612,7 @@ fn layout_delimiters(
     if let Some(left) = left {
         let mut left = GlyphFragment::new(ctx, styles, left, span)
             .stretch_vertical(ctx, target, short_fall);
-        left.center_on_axis(ctx);
+        left.align_on_axis(ctx, delimiter_alignment(left.c));
         ctx.push(left);
     }
 
@@ -619,7 +621,7 @@ fn layout_delimiters(
     if let Some(right) = right {
         let mut right = GlyphFragment::new(ctx, styles, right, span)
             .stretch_vertical(ctx, target, short_fall);
-        right.center_on_axis(ctx);
+        right.align_on_axis(ctx, delimiter_alignment(right.c));
         ctx.push(right);
     }
 

crates/typst/src/math/mod.rs

@@ -46,7 +46,7 @@ use crate::foundations::{
     StyledElem,
 };
 use crate::introspection::TagElem;
-use crate::layout::{BoxElem, Frame, FrameItem, HElem, Point, Size, Spacing};
+use crate::layout::{BoxElem, Frame, FrameItem, HElem, Point, Size, Spacing, VAlignment};
 use crate::realize::{process, BehavedBuilder};
 use crate::text::{LinebreakElem, SpaceElem, TextElem};
 
@@ -317,3 +317,11 @@ impl LayoutMath for Content {
         Ok(())
     }
 }
+
+fn delimiter_alignment(delimiter: char) -> VAlignment {
+    match delimiter {
+        '\u{231c}' | '\u{231d}' => VAlignment::Top,
+        '\u{231e}' | '\u{231f}' => VAlignment::Bottom,
+        _ => VAlignment::Horizon,
+    }
+}

tests/suite/math/delimited.typ

@@ -62,3 +62,7 @@ $ 1/(2 y (x) (2(3)) $
 // Test ignoring weak spacing immediately after the opening
 // and immediately before the closing.
 $ [#h(1em, weak: true)A(dif x, f(x) dif x)sum#h(1em, weak: true)] $
+
+--- issue-4188-lr-corner-brackets ---
+// Test positioning of U+231C to U+231F
+$⌜a⌟⌞b⌝$ = $⌜$$a$$⌟$$⌞$$b$$⌝$