Merge 8c811110f3fa3815a3c722107e3383fdf8075ad2 into e9f1b5825a9d37ca0c173a7b2830ba36a27ca9e0

Takes either a function or a relative length, just like with `lr`,
`stretch`, and `accent` which was changed in the previous two commits.
The default is now much clearer to the user: `x => x * 1.1 - 0.1em`.

Cargo.toml

@@ -159,6 +159,7 @@ strip = true
 [workspace.lints.clippy]
 blocks_in_conditions = "allow"
 comparison_chain = "allow"
+iter_over_hash_type = "warn"
 manual_range_contains = "allow"
 mutable_key_type = "allow"
 uninlined_format_args = "warn"

crates/typst-cli/src/watch.rs

@@ -139,6 +139,7 @@ impl Watcher {
     fn update(&mut self, iter: impl IntoIterator<Item = PathBuf>) -> StrResult<()> {
         // Mark all files as not "seen" so that we may unwatch them if they
         // aren't in the dependency list.
+        #[allow(clippy::iter_over_hash_type, reason = "order does not matter")]
         for seen in self.watched.values_mut() {
             *seen = false;
         }

crates/typst-cli/src/world.rs

@@ -173,6 +173,7 @@ impl SystemWorld {
 
     /// Reset the compilation state in preparation of a new compilation.
     pub fn reset(&mut self) {
+        #[allow(clippy::iter_over_hash_type, reason = "order does not matter")]
         for slot in self.slots.get_mut().values_mut() {
             slot.reset();
         }

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

@@ -1,6 +1,6 @@
 use typst_library::diag::SourceResult;
 use typst_library::foundations::{Packed, StyleChain};
-use typst_library::layout::{Em, Frame, Point, Size};
+use typst_library::layout::{Frame, Point, Size};
 use typst_library::math::AccentElem;
 
 use super::{
@@ -8,9 +8,6 @@ use super::{
     style_flac,
 };
 
-/// How much the accent can be shorter than the base.
-const ACCENT_SHORT_FALL: Em = Em::new(0.5);
-
 /// Lays out an [`AccentElem`].
 #[typst_macros::time(name = "math.accent", span = elem.span())]
 pub fn layout_accent(
@@ -45,11 +42,8 @@ pub fn layout_accent(
     let mut glyph =
         GlyphFragment::new_char(ctx.font, accent_styles, accent.0, elem.span())?;
 
-    // Forcing the accent to be at least as large as the base makes it too wide
-    // in many cases.
-    let width = elem.size.resolve(styles).relative_to(base.width());
-    let short_fall = ACCENT_SHORT_FALL.at(glyph.item.size);
-    glyph.stretch_horizontal(ctx, width - short_fall);
+    let width = elem.size.get_ref(styles).resolve(ctx.engine, styles, base.width())?;
+    glyph.stretch_horizontal(ctx, width);
     let accent_attach = glyph.accent_attach.0;
     let accent = glyph.into_frame();
 

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

@@ -1,8 +1,9 @@
 use typst_library::diag::SourceResult;
 use typst_library::foundations::{Packed, StyleChain, SymbolElem};
-use typst_library::layout::{Abs, Axis, Corner, Frame, Point, Rel, Size};
+use typst_library::layout::{Abs, Axis, Corner, Frame, Point, Size};
 use typst_library::math::{
     AttachElem, EquationElem, LimitsElem, PrimesElem, ScriptsElem, StretchElem,
+    StretchSize,
 };
 use typst_utils::OptionExt;
 
@@ -66,12 +67,12 @@ pub fn layout_attach(
         let relative_to_width = measure!(t, width).max(measure!(b, width));
         stretch_fragment(
             ctx,
+            styles,
             &mut base,
             Some(Axis::X),
             Some(relative_to_width),
-            stretch,
-            Abs::zero(),
-        );
+            &stretch,
+        )?;
     }
 
     let fragments = [
@@ -154,7 +155,7 @@ pub fn layout_limits(
 }
 
 /// Get the size to stretch the base to.
-fn stretch_size(styles: StyleChain, elem: &Packed<AttachElem>) -> Option<Rel<Abs>> {
+fn stretch_size(styles: StyleChain, elem: &Packed<AttachElem>) -> Option<StretchSize> {
     // Extract from an EquationElem.
     let mut base = &elem.base;
     while let Some(equation) = base.to_packed::<EquationElem>() {
@@ -162,7 +163,7 @@ fn stretch_size(styles: StyleChain, elem: &Packed<AttachElem>) -> Option<Rel<Abs
     }
 
     base.to_packed::<StretchElem>()
-        .map(|stretch| stretch.size.resolve(styles))
+        .map(|stretch| stretch.size.get_cloned(styles))
 }
 
 /// Lay out the attachments.

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

@@ -1,14 +1,13 @@
 use typst_library::diag::SourceResult;
 use typst_library::foundations::{Content, Packed, Resolve, StyleChain, SymbolElem};
 use typst_library::layout::{Em, Frame, FrameItem, Point, Size};
-use typst_library::math::{BinomElem, FracElem};
+use typst_library::math::{BinomElem, DELIM_SHORT_FALL, FracElem};
 use typst_library::text::TextElem;
 use typst_library::visualize::{FixedStroke, Geometry};
 use typst_syntax::Span;
 
 use super::{
-    DELIM_SHORT_FALL, FrameFragment, GlyphFragment, MathContext, style_for_denominator,
-    style_for_numerator,
+    FrameFragment, GlyphFragment, MathContext, style_for_denominator, style_for_numerator,
 };
 
 const FRAC_AROUND: Em = Em::new(0.1);
@@ -49,7 +48,7 @@ fn layout_frac_like(
     binom: bool,
     span: Span,
 ) -> SourceResult<()> {
-    let short_fall = DELIM_SHORT_FALL.resolve(styles);
+    let short_fall = DELIM_SHORT_FALL.abs().resolve(styles);
     let axis = scaled!(ctx, styles, axis_height);
     let thickness = scaled!(ctx, styles, fraction_rule_thickness);
     let shift_up = scaled!(

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

@@ -1,11 +1,11 @@
 use typst_library::diag::SourceResult;
 use typst_library::foundations::{Packed, StyleChain};
-use typst_library::layout::{Abs, Axis, Rel};
-use typst_library::math::{EquationElem, LrElem, MidElem};
+use typst_library::layout::{Abs, Axis};
+use typst_library::math::{EquationElem, LrElem, MidElem, StretchSize};
 use typst_utils::SliceExt;
 use unicode_math_class::MathClass;
 
-use super::{DELIM_SHORT_FALL, MathContext, MathFragment, stretch_fragment};
+use super::{MathContext, MathFragment, stretch_fragment};
 
 /// Lays out an [`LrElem`].
 #[typst_macros::time(name = "math.lr", span = elem.span())]
@@ -22,7 +22,7 @@ pub fn layout_lr(
 
     // Extract implicit LrElem.
     if let Some(lr) = body.to_packed::<LrElem>()
-        && lr.size.get(styles).is_one()
+        && lr.size.get_ref(styles).is_lr_default()
     {
         body = &lr.body;
     }
@@ -41,14 +41,28 @@ pub fn layout_lr(
         .unwrap_or_default();
 
     let relative_to = 2.0 * max_extent;
-    let height = elem.size.resolve(styles);
+    let height = elem.size.get_ref(styles);
 
     // Scale up fragments at both ends.
     match inner_fragments {
-        [one] => scale_if_delimiter(ctx, one, relative_to, height, None),
+        [one] => scale_if_delimiter(ctx, styles, one, relative_to, height, None)?,
         [first, .., last] => {
-            scale_if_delimiter(ctx, first, relative_to, height, Some(MathClass::Opening));
-            scale_if_delimiter(ctx, last, relative_to, height, Some(MathClass::Closing));
+            scale_if_delimiter(
+                ctx,
+                styles,
+                first,
+                relative_to,
+                height,
+                Some(MathClass::Opening),
+            )?;
+            scale_if_delimiter(
+                ctx,
+                styles,
+                last,
+                relative_to,
+                height,
+                Some(MathClass::Closing),
+            )?;
         }
         [] => {}
     }
@@ -59,7 +73,7 @@ pub fn layout_lr(
             && glyph.mid_stretched == Some(false)
         {
             glyph.mid_stretched = Some(true);
-            scale(ctx, fragment, relative_to, height);
+            scale(ctx, styles, fragment, relative_to, height)?;
         }
     }
 
@@ -112,32 +126,32 @@ pub fn layout_mid(
 /// it is a delimiter, in a way that cannot be overridden by the user.
 fn scale_if_delimiter(
     ctx: &mut MathContext,
+    styles: StyleChain,
     fragment: &mut MathFragment,
     relative_to: Abs,
-    height: Rel<Abs>,
+    height: &StretchSize,
     apply: Option<MathClass>,
-) {
+) -> SourceResult<()> {
     if matches!(
         fragment.class(),
         MathClass::Opening | MathClass::Closing | MathClass::Fence
     ) {
-        scale(ctx, fragment, relative_to, height);
+        scale(ctx, styles, fragment, relative_to, height)?;
 
         if let Some(class) = apply {
             fragment.set_class(class);
         }
     }
+    Ok(())
 }
 
 /// Scales a math fragment to a height.
 fn scale(
     ctx: &mut MathContext,
+    styles: StyleChain,
     fragment: &mut MathFragment,
     relative_to: Abs,
-    height: Rel<Abs>,
-) {
-    // This unwrap doesn't really matter. If it is None, then the fragment
-    // won't be stretchable anyways.
-    let short_fall = DELIM_SHORT_FALL.at(fragment.font_size().unwrap_or_default());
-    stretch_fragment(ctx, fragment, Some(Axis::Y), Some(relative_to), height, short_fall);
+    height: &StretchSize,
+) -> SourceResult<()> {
+    stretch_fragment(ctx, styles, fragment, Some(Axis::Y), Some(relative_to), height)
 }

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

@@ -1,19 +1,20 @@
 use typst_library::diag::{SourceResult, bail, warning};
 use typst_library::foundations::{Content, Packed, Resolve, StyleChain};
 use typst_library::layout::{
-    Abs, Axes, Em, FixedAlignment, Frame, FrameItem, Point, Ratio, Rel, Size,
+    Abs, Axes, Em, FixedAlignment, Frame, FrameItem, Point, Rel, Size,
+};
+use typst_library::math::{
+    Augment, AugmentOffsets, CasesElem, MatElem, StretchSize, VecElem,
 };
-use typst_library::math::{Augment, AugmentOffsets, CasesElem, MatElem, VecElem};
 use typst_library::text::TextElem;
 use typst_library::visualize::{FillRule, FixedStroke, Geometry, LineCap, Shape};
 use typst_syntax::Span;
 
 use super::{
-    AlignmentResult, DELIM_SHORT_FALL, FrameFragment, GlyphFragment, LeftRightAlternator,
-    MathContext, alignments, style_for_denominator,
+    AlignmentResult, FrameFragment, GlyphFragment, LeftRightAlternator, MathContext,
+    alignments, style_for_denominator,
 };
 
-const VERTICAL_PADDING: Ratio = Ratio::new(0.1);
 const DEFAULT_STROKE_THICKNESS: Em = Em::new(0.05);
 
 /// Lays out a [`VecElem`].
@@ -39,7 +40,15 @@ pub fn layout_vec(
     )?;
 
     let delim = elem.delim.get(styles);
-    layout_delimiters(ctx, styles, frame, delim.open(), delim.close(), span)
+    layout_delimiters(
+        ctx,
+        styles,
+        frame,
+        elem.delim_size.get_ref(styles),
+        delim.open(),
+        delim.close(),
+        span,
+    )
 }
 
 /// Lays out a [`CasesElem`].
@@ -70,7 +79,15 @@ pub fn layout_cases(
     } else {
         (delim.open(), None)
     };
-    layout_delimiters(ctx, styles, frame, open, close, span)
+    layout_delimiters(
+        ctx,
+        styles,
+        frame,
+        elem.delim_size.get_ref(styles),
+        open,
+        close,
+        span,
+    )
 }
 
 /// Lays out a [`MatElem`].
@@ -128,7 +145,15 @@ pub fn layout_mat(
     )?;
 
     let delim = elem.delim.get(styles);
-    layout_delimiters(ctx, styles, frame, delim.open(), delim.close(), span)
+    layout_delimiters(
+        ctx,
+        styles,
+        frame,
+        elem.delim_size.get_ref(styles),
+        delim.open(),
+        delim.close(),
+        span,
+    )
 }
 
 /// Layout the inner contents of a matrix, vector, or cases.
@@ -309,19 +334,20 @@ fn layout_delimiters(
     ctx: &mut MathContext,
     styles: StyleChain,
     mut frame: Frame,
+    size: &StretchSize,
     left: Option<char>,
     right: Option<char>,
     span: Span,
 ) -> SourceResult<()> {
-    let short_fall = DELIM_SHORT_FALL.resolve(styles);
     let axis = scaled!(ctx, styles, axis_height);
     let height = frame.height();
-    let target = height + VERTICAL_PADDING.of(height);
     frame.set_baseline(height / 2.0 + axis);
 
+    let target = size.resolve(ctx.engine, styles, height)?;
+
     if let Some(left_c) = left {
         let mut left = GlyphFragment::new_char(ctx.font, styles, left_c, span)?;
-        left.stretch_vertical(ctx, target - short_fall);
+        left.stretch_vertical(ctx, target);
         left.center_on_axis();
         ctx.push(left);
     }
@@ -330,7 +356,7 @@ fn layout_delimiters(
 
     if let Some(right_c) = right {
         let mut right = GlyphFragment::new_char(ctx.font, styles, right_c, span)?;
-        right.stretch_vertical(ctx, target - short_fall);
+        right.stretch_vertical(ctx, target);
         right.center_on_axis();
         ctx.push(right);
     }

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

@@ -1,7 +1,7 @@
 use ttf_parser::Tag;
 use ttf_parser::math::MathValue;
 use typst_library::foundations::{Style, StyleChain};
-use typst_library::layout::{Abs, Em, FixedAlignment, Frame, Point, Size};
+use typst_library::layout::{Abs, FixedAlignment, Frame, Point, Size};
 use typst_library::math::{EquationElem, MathSize};
 use typst_library::text::{FontFeatures, TextElem};
 use typst_utils::LazyHash;
@@ -30,9 +30,6 @@ macro_rules! percent {
     };
 }
 
-/// How much less high scaled delimiters can be than what they wrap.
-pub const DELIM_SHORT_FALL: Em = Em::new(0.1);
-
 /// Converts some unit to an absolute length with the current font & font size.
 pub trait Scaled {
     fn scaled(self, ctx: &MathContext, font_size: Abs) -> Abs;

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

@@ -1,7 +1,7 @@
 use typst_library::diag::{SourceResult, warning};
 use typst_library::foundations::{Packed, StyleChain};
-use typst_library::layout::{Abs, Axis, Rel};
-use typst_library::math::StretchElem;
+use typst_library::layout::{Abs, Axis};
+use typst_library::math::{StretchElem, StretchSize};
 use typst_utils::Get;
 
 use super::{MathContext, MathFragment, stretch_axes};
@@ -14,14 +14,7 @@ pub fn layout_stretch(
     styles: StyleChain,
 ) -> SourceResult<()> {
     let mut fragment = ctx.layout_into_fragment(&elem.body, styles)?;
-    stretch_fragment(
-        ctx,
-        &mut fragment,
-        None,
-        None,
-        elem.size.resolve(styles),
-        Abs::zero(),
-    );
+    stretch_fragment(ctx, styles, &mut fragment, None, None, elem.size.get_ref(styles))?;
     ctx.push(fragment);
     Ok(())
 }
@@ -29,29 +22,29 @@ pub fn layout_stretch(
 /// Attempts to stretch the given fragment by/to the amount given in stretch.
 pub fn stretch_fragment(
     ctx: &mut MathContext,
+    styles: StyleChain,
     fragment: &mut MathFragment,
     axis: Option<Axis>,
     relative_to: Option<Abs>,
-    stretch: Rel<Abs>,
-    short_fall: Abs,
-) {
+    stretch: &StretchSize,
+) -> SourceResult<()> {
     let size = fragment.size();
 
-    let MathFragment::Glyph(glyph) = fragment else { return };
+    let MathFragment::Glyph(glyph) = fragment else { return Ok(()) };
 
     // Return if we attempt to stretch along an axis which isn't stretchable,
     // so that the original fragment isn't modified.
     let axes = stretch_axes(&glyph.item.font, glyph.base_glyph.id);
     let stretch_axis = if let Some(axis) = axis {
         if !axes.get(axis) {
-            return;
+            return Ok(());
         }
         axis
     } else {
         match (axes.x, axes.y) {
             (true, false) => Axis::X,
             (false, true) => Axis::Y,
-            (false, false) => return,
+            (false, false) => return Ok(()),
             (true, true) => {
                 // As far as we know, there aren't any glyphs that have both
                 // vertical and horizontal constructions. So for the time being, we
@@ -62,16 +55,19 @@ pub fn stretch_fragment(
                    hint: "this is probably a font bug";
                    hint: "please file an issue at https://github.com/typst/typst/issues"
                 ));
-                return;
+                return Ok(());
             }
         }
     };
 
     let relative_to_size = relative_to.unwrap_or_else(|| size.get(stretch_axis));
+    let target = stretch.resolve(ctx.engine, styles, relative_to_size)?;
 
-    glyph.stretch(ctx, stretch.relative_to(relative_to_size) - short_fall, stretch_axis);
+    glyph.stretch(ctx, target, stretch_axis);
 
     if stretch_axis == Axis::Y {
         glyph.center_on_axis();
     }
+
+    Ok(())
 }

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

@@ -6,9 +6,21 @@ use icu_provider::AsDeserializingBufferProvider;
 use icu_provider_blob::BlobDataProvider;
 
 use crate::diag::bail;
-use crate::foundations::{Content, NativeElement, SymbolElem, cast, elem, func};
-use crate::layout::{Length, Rel};
-use crate::math::Mathy;
+use crate::foundations::{
+    Content, NativeElement, NativeFunc, SymbolElem, cast, elem, func,
+};
+use crate::layout::{Em, Length, Ratio, Rel};
+use crate::math::{Mathy, StretchSize};
+
+const ACCENT_SHORT_FALL: Em = Em::new(-0.5);
+
+#[func(name = "x => x - 0.5em")]
+const fn default_accent_size(base: Length) -> Rel {
+    Rel {
+        rel: Ratio::zero(),
+        abs: Length { abs: base.abs, em: ACCENT_SHORT_FALL },
+    }
+}
 
 /// Attaches an accent to a base.
 ///
@@ -59,11 +71,14 @@ pub struct AccentElem {
 
     /// The size of the accent, relative to the width of the base.
     ///
+    /// See the [stretch documentation]($math.stretch.size) for more
+    /// information on sizes.
+    ///
     /// ```example
     /// $dash(A, size: #150%)$
     /// ```
-    #[default(Rel::one())]
-    pub size: Rel<Length>,
+    #[default(<default_accent_size>::data().into())]
+    pub size: StretchSize,
 
     /// Whether to remove the dot on top of lowercase i and j when adding a top
     /// accent.
@@ -140,8 +155,11 @@ macro_rules! accents {
                 /// The base to which the accent is applied.
                 base: Content,
                 /// The size of the accent, relative to the width of the base.
+                ///
+                /// See the [stretch documentation]($math.stretch.size) for
+                /// more information on sizes.
                 #[named]
-                size: Option<Rel<Length>>,
+                size: Option<StretchSize>,
                 /// Whether to remove the dot on top of lowercase i and j when
                 /// adding a top accent.
                 #[named]

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

@@ -1,5 +1,4 @@
 use crate::foundations::{Content, Packed, elem};
-use crate::layout::{Length, Rel};
 use crate::math::{EquationElem, Mathy};
 
 /// A base with optional attachments.
@@ -128,30 +127,3 @@ pub struct LimitsElem {
     #[default(true)]
     pub inline: bool,
 }
-
-/// Stretches a glyph.
-///
-/// This function can also be used to automatically stretch the base of an
-/// attachment, so that it fits the top and bottom attachments.
-///
-/// Note that only some glyphs can be stretched, and which ones can depend on
-/// the math font being used. However, most math fonts are the same in this
-/// regard.
-///
-/// ```example
-/// $ H stretch(=)^"define" U + p V $
-/// $ f : X stretch(->>, size: #150%)_"surjective" Y $
-/// $ x stretch(harpoons.ltrb, size: #3em) y
-///     stretch(\[, size: #150%) z $
-/// ```
-#[elem(Mathy)]
-pub struct StretchElem {
-    /// The glyph to stretch.
-    #[required]
-    pub body: Content,
-
-    /// The size to stretch to, relative to the maximum size of the glyph and
-    /// its attachments.
-    #[default(Rel::one())]
-    pub size: Rel<Length>,
-}

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

@@ -1,6 +1,16 @@
-use crate::foundations::{Content, NativeElement, SymbolElem, elem, func};
-use crate::layout::{Length, Rel};
-use crate::math::Mathy;
+use crate::foundations::{Content, NativeElement, NativeFunc, SymbolElem, elem, func};
+use crate::layout::{Em, Length, Ratio, Rel};
+use crate::math::{Mathy, StretchSize};
+
+pub const DELIM_SHORT_FALL: Em = Em::new(-0.1);
+
+#[func(name = "x => x - 0.1em")]
+pub const fn default_lr_size(base: Length) -> Rel {
+    Rel {
+        rel: Ratio::zero(),
+        abs: Length { abs: base.abs, em: DELIM_SHORT_FALL },
+    }
+}
 
 /// Scales delimiters.
 ///
@@ -8,9 +18,13 @@ use crate::math::Mathy;
 /// unmatched delimiters and to control the delimiter scaling more precisely.
 #[elem(title = "Left/Right", Mathy)]
 pub struct LrElem {
-    /// The size of the brackets, relative to the height of the wrapped content.
-    #[default(Rel::one())]
-    pub size: Rel<Length>,
+    /// The size of the delimiters, relative to the height of the wrapped
+    /// content.
+    ///
+    /// See the [stretch documentation]($math.stretch.size) for more
+    /// information on sizes.
+    #[default(<default_lr_size>::data().into())]
+    pub size: StretchSize,
 
     /// The delimited content, including the delimiters.
     #[required]
@@ -42,9 +56,13 @@ pub struct MidElem {
 /// ```
 #[func]
 pub fn floor(
-    /// The size of the brackets, relative to the height of the wrapped content.
+    /// The size of the delimiters, relative to the height of the wrapped
+    /// content.
+    ///
+    /// See the [stretch documentation]($math.stretch.size) for more
+    /// information on sizes.
     #[named]
-    size: Option<Rel<Length>>,
+    size: Option<StretchSize>,
     /// The expression to floor.
     body: Content,
 ) -> Content {
@@ -58,9 +76,13 @@ pub fn floor(
 /// ```
 #[func]
 pub fn ceil(
-    /// The size of the brackets, relative to the height of the wrapped content.
+    /// The size of the delimiters, relative to the height of the wrapped
+    /// content.
+    ///
+    /// See the [stretch documentation]($math.stretch.size) for more
+    /// information on sizes.
     #[named]
-    size: Option<Rel<Length>>,
+    size: Option<StretchSize>,
     /// The expression to ceil.
     body: Content,
 ) -> Content {
@@ -74,9 +96,13 @@ pub fn ceil(
 /// ```
 #[func]
 pub fn round(
-    /// The size of the brackets, relative to the height of the wrapped content.
+    /// The size of the delimiters, relative to the height of the wrapped
+    /// content.
+    ///
+    /// See the [stretch documentation]($math.stretch.size) for more
+    /// information on sizes.
     #[named]
-    size: Option<Rel<Length>>,
+    size: Option<StretchSize>,
     /// The expression to round.
     body: Content,
 ) -> Content {
@@ -90,9 +116,13 @@ pub fn round(
 /// ```
 #[func]
 pub fn abs(
-    /// The size of the brackets, relative to the height of the wrapped content.
+    /// The size of the delimiters, relative to the height of the wrapped
+    /// content.
+    ///
+    /// See the [stretch documentation]($math.stretch.size) for more
+    /// information on sizes.
     #[named]
-    size: Option<Rel<Length>>,
+    size: Option<StretchSize>,
     /// The expression to take the absolute value of.
     body: Content,
 ) -> Content {
@@ -106,9 +136,13 @@ pub fn abs(
 /// ```
 #[func]
 pub fn norm(
-    /// The size of the brackets, relative to the height of the wrapped content.
+    /// The size of the delimiters, relative to the height of the wrapped
+    /// content.
+    ///
+    /// See the [stretch documentation]($math.stretch.size) for more
+    /// information on sizes.
     #[named]
-    size: Option<Rel<Length>>,
+    size: Option<StretchSize>,
     /// The expression to take the norm of.
     body: Content,
 ) -> Content {
@@ -119,7 +153,7 @@ fn delimited(
     body: Content,
     left: char,
     right: char,
-    size: Option<Rel<Length>>,
+    size: Option<StretchSize>,
 ) -> Content {
     let span = body.span();
     let mut elem = LrElem::new(Content::sequence([

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

@@ -5,15 +5,27 @@ use unicode_math_class::MathClass;
 
 use crate::diag::{At, HintedStrResult, StrResult, bail};
 use crate::foundations::{
-    Array, Content, Dict, Fold, NoneValue, Resolve, Smart, StyleChain, Symbol, Value,
-    array, cast, dict, elem,
+    Array, Content, Dict, Fold, NativeFunc, NoneValue, Resolve, Smart, StyleChain,
+    Symbol, Value, array, cast, dict, elem, func,
 };
-use crate::layout::{Abs, Em, HAlignment, Length, Rel};
-use crate::math::Mathy;
+use crate::layout::{Abs, Em, HAlignment, Length, Ratio, Rel};
+use crate::math::{DELIM_SHORT_FALL, Mathy, StretchSize};
 use crate::visualize::Stroke;
 
 const DEFAULT_ROW_GAP: Em = Em::new(0.2);
 const DEFAULT_COL_GAP: Em = Em::new(0.5);
+const VERTICAL_PADDING: Ratio = Ratio::new(1.1);
+
+#[func(name = "x => x * 1.1 - 0.1em")]
+const fn default_mat_size(base: Length) -> Rel {
+    Rel {
+        rel: Ratio::zero(),
+        abs: Length {
+            abs: Abs::raw(base.abs.to_raw() * VERTICAL_PADDING.get()),
+            em: DELIM_SHORT_FALL,
+        },
+    }
+}
 
 /// A column vector.
 ///
@@ -40,6 +52,13 @@ pub struct VecElem {
     #[default(DelimiterPair::PAREN)]
     pub delim: DelimiterPair,
 
+    /// The size of the delimiters, relative to the elements' total height.
+    ///
+    /// See the [stretch documentation]($math.stretch.size) for more
+    /// information on sizes.
+    #[default(<default_mat_size>::data().into())]
+    pub delim_size: StretchSize,
+
     /// The horizontal alignment that each element should have.
     ///
     /// ```example
@@ -99,6 +118,13 @@ pub struct MatElem {
     #[default(DelimiterPair::PAREN)]
     pub delim: DelimiterPair,
 
+    /// The size of the delimiters, relative to the cells' total height.
+    ///
+    /// See the [stretch documentation]($math.stretch.size) for more
+    /// information on sizes.
+    #[default(<default_mat_size>::data().into())]
+    pub delim_size: StretchSize,
+
     /// The horizontal alignment that each cell should have.
     ///
     /// ```example
@@ -238,6 +264,13 @@ pub struct CasesElem {
     #[default(DelimiterPair::BRACE)]
     pub delim: DelimiterPair,
 
+    /// The size of the delimiters, relative to the branches' total height.
+    ///
+    /// See the [stretch documentation]($math.stretch.size) for more
+    /// information on sizes.
+    #[default(<default_mat_size>::data().into())]
+    pub delim_size: StretchSize,
+
     /// Whether the direction of cases should be reversed.
     ///
     /// ```example

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

@@ -9,6 +9,7 @@ mod lr;
 mod matrix;
 mod op;
 mod root;
+mod stretch;
 mod style;
 mod underover;
 
@@ -21,6 +22,7 @@ pub use self::lr::*;
 pub use self::matrix::*;
 pub use self::op::*;
 pub use self::root::*;
+pub use self::stretch::*;
 pub use self::style::*;
 pub use self::underover::*;
 

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

@@ -0,0 +1,125 @@
+use comemo::Track;
+
+use crate::diag::{At, SourceResult};
+use crate::engine::Engine;
+use crate::foundations::{
+    Content, Context, Func, NativeFunc, NativeFuncData, Resolve, StyleChain, cast, elem,
+};
+use crate::layout::{Abs, Rel};
+use crate::math::{Mathy, default_lr_size};
+
+/// Stretches a glyph.
+///
+/// This function can also be used to automatically stretch the base of an
+/// attachment, so that it fits the top and bottom attachments.
+///
+/// Note that only some glyphs can be stretched, and which ones can depend on
+/// the math font being used. However, most math fonts are the same in this
+/// regard.
+///
+/// ```example
+/// $ H stretch(=)^"define" U + p V $
+/// $ f : X stretch(->>, size: #150%)_"surjective" Y $
+/// $ x stretch(harpoons.ltrb, size: #3em) y
+///     stretch(\[, size: #150%) z $
+/// ```
+#[elem(Mathy)]
+pub struct StretchElem {
+    /// The glyph to stretch.
+    #[required]
+    pub body: Content,
+
+    /// The size to stretch to, relative to the maximum size of the glyph and
+    /// its attachments.
+    ///
+    /// This value can be given as a [relative length]($relative), or a
+    /// [function]($function) that receives the size of the glyph as a
+    /// parameter (an absolute length) and should return a (relative) length.
+    /// For example, `{x => x * 80%}` would be equivalent to just specifying `{80%}`.
+    ///
+    /// Note that the sizes of glyphs in math fonts come about in two ways:
+    ///
+    /// - First, there are pre-made variants at specific sizes. This means you
+    ///   will see discrete jumps in the stretched glyph's size as you increase
+    ///   the size parameter. It is up to the font how many pre-made variants
+    ///   there are and what their sizes are.
+    ///
+    /// - Then, if the pre-made variants are all too small, a glyph of the
+    ///   desired size is assembled from parts. The stretched glyph's size will
+    ///   now be the exact size requested.
+    ///
+    /// It could be the case that only one of the above exist for a glyph in
+    /// the font.
+    ///
+    /// The value given here is really a minimum (but if there is no assembly
+    /// for the glyph, this minimum may not be reached), so the actual size of
+    /// the stretched glyph may not match what you specified.
+    ///
+    /// ```example
+    /// #for i in range(0, 15) {
+    ///   $stretch(\[, size: #(10pt + i * 2pt))$
+    /// }
+    ///
+    /// #set math.stretch(size: x => x + 0.5em)
+    /// $x stretch(=)^"def" y$
+    /// ```
+    #[default(Rel::one().into())]
+    pub size: StretchSize,
+}
+
+/// How to size a stretched glyph.
+#[derive(Debug, Clone, PartialEq, Hash)]
+pub enum StretchSize {
+    /// Sized by the specified length.
+    Rel(Rel),
+    /// Resolve the size for the given base size through the specified
+    /// function.
+    Func(Func),
+}
+
+impl StretchSize {
+    /// Resolve the stretch size given the base size.
+    pub fn resolve(
+        &self,
+        engine: &mut Engine,
+        styles: StyleChain,
+        base: Abs,
+    ) -> SourceResult<Abs> {
+        Ok(match self {
+            Self::Rel(rel) => *rel,
+            Self::Func(func) => func
+                .call(engine, Context::new(None, Some(styles)).track(), [base])?
+                .cast()
+                .at(func.span())?,
+        }
+        .resolve(styles)
+        .relative_to(base))
+    }
+
+    /// Whether the size is the default used by `LrElem`.
+    pub fn is_lr_default(&self) -> bool {
+        *self == <default_lr_size>::data().into()
+    }
+}
+
+impl From<Rel> for StretchSize {
+    fn from(rel: Rel) -> Self {
+        Self::Rel(rel)
+    }
+}
+
+impl From<&'static NativeFuncData> for StretchSize {
+    fn from(data: &'static NativeFuncData) -> Self {
+        Self::Func(Func::from(data))
+    }
+}
+
+cast! {
+    StretchSize,
+    self => match self {
+        Self::Rel(v) => v.into_value(),
+        Self::Func(v) => v.into_value(),
+    },
+    v: Rel => Self::Rel(v),
+    v: Func => Self::Func(v),
+}

tests/suite/math/accent.typ

@@ -30,11 +30,17 @@ $ tilde(integral), tilde(integral)_a^b, tilde(integral_a^b) $
 
 --- math-accent-sized ---
 // Test accent size.
-$tilde(sum), tilde(sum, size: #50%), accent(H, hat, size: #200%)$
+$tilde(sum), tilde(sum, size: #25%), accent(H, hat, size: #125%)$
 
 --- math-accent-sized-script ---
 // Test accent size in script size.
-$tilde(U, size: #1.1em), x^tilde(U, size: #1.1em), sscript(tilde(U, size: #1.1em))$
+$tilde(U, size: #0.6em), x^tilde(U, size: #0.6em), sscript(tilde(U, size: #0.6em))$
+
+--- math-accent-sized-function ---
+// Test accent size with a function.
+$dash(A) arrow(I) hat(L)$ \
+#set math.accent(size: x => x - 0.1em)
+$dash(A) arrow(I) hat(L)$
 
 --- math-accent-dotless ---
 // Test dotless glyph variants.
@@ -85,7 +91,7 @@ $ accent(integral, \u{20EC}), accent(integral, \u{20EC})_a^b, accent(integral_a^
 
 --- math-accent-bottom-sized ---
 // Test bottom accent size.
-$accent(sum, \u{0330}), accent(sum, \u{0330}, size: #50%), accent(H, \u{032D}, size: #200%)$
+$accent(sum, \u{0330}), accent(sum, \u{0330}, size: #25%), accent(H, \u{032D}, size: #125%)$
 
 --- math-accent-nested ---
 // Test nested top and bottom accents.

tests/suite/math/attach.typ

@@ -187,5 +187,5 @@ $ a0 + a1 + a0_2 \
 --- math-attach-scripts-extended-shapes ---
 // Test script attachments positioning if the base is an extended shape (or a
 // sequence of extended shapes).
-$lr(size: #130%, [x])_0^1, [x]_0^1, \]_0^1, x_0^1, A_0^1$ \
+$lr(size: #115%, [x])_0^1, [x]_0^1, \]_0^1, x_0^1, A_0^1$ \
 $n^2, (n + 1)^2, sum_0^1, integral_0^1$

tests/suite/math/cases.typ

@@ -16,6 +16,12 @@ $ x = cases(1, 2) $
 #set math.cases(delim: sym.angle.l)
 $ cases(a, b, c) $
 
+--- math-cases-delim-size ---
+// Test setting delimiter size.
+$ cases(reverse: #true, 1, 2, 3) cases(delim-size: #100%, 1, 2, 3) $
+#set math.cases(delim-size: x => calc.max(x - 5pt, x * 0.901))
+$ cases(1, 2) cases(1, 2, 3, 4) $
+
 --- math-cases-linebreaks ---
 // Warning: 40-49 linebreaks are ignored in branches
 // Hint: 40-49 use commas instead to separate each line

tests/suite/math/delimited.typ

@@ -31,9 +31,14 @@ $ lr(a/b\]) = a = lr(\{a/b) $
 
 --- math-lr-size ---
 // Test manual scaling.
-$ lr(]sum_(x=1)^n x], size: #70%)
+$ lr(]sum_(x=1)^n x], size: #60%)
   < lr((1, 2), size: #200%) $
 
+--- math-lr-size-function ---
+// Test using a function as an argument to size.
+#set math.lr(size: x => if x > 10pt { 1em } else { 4 * x })
+$ (a) (1/2) $
+
 --- math-lr-shorthands ---
 // Test predefined delimiter pairings.
 $floor(x/2), ceil(x/2), abs(x), norm(x)$
@@ -57,16 +62,16 @@ $ { x mid(|) sum_(i=1)^oo phi_i (x) < 1 } \
 #set page(width: auto)
 
 $ lr({ A mid(|) integral }) quad
-  lr(size: #1em, { A mid(|) integral }) quad
-  lr(size: #(1em+20%), { A mid(|) integral }) \
+  lr(size: #0%, { A mid(|) integral }) quad
+  lr(size: #(1em+10%), { A mid(|) integral }) \
 
   lr(] A mid(|) integral ]) quad
-  lr(size: #1em, ] A mid(|) integral ]) quad
-  lr(size: #(1em+20%), ] A mid(|) integral ]) \
+  lr(size: #0%, ] A mid(|) integral ]) quad
+  lr(size: #(1em+10%), ] A mid(|) integral ]) \
 
   lr(( A mid(|) integral ]) quad
-  lr(size: #1em, ( A mid(|) integral ]) quad
-  lr(size: #(1em+20%), ( A mid(|) integral ]) $
+  lr(size: #0%, ( A mid(|) integral ]) quad
+  lr(size: #(1em+10%), ( A mid(|) integral ]) $
 
 --- math-lr-mid-size-nested-equation ---
 // Test mid size when lr size is set, when nested in an equation.
@@ -74,8 +79,8 @@ $ lr({ A mid(|) integral }) quad
 
 #let body = ${ A mid(|) integral }$
 $ lr(body) quad
-  lr(size: #1em, body) quad
-  lr(size: #(1em+20%), body) $
+  lr(size: #0%, body) quad
+  lr(size: #(1em+10%), body) $
 
 --- math-lr-mid-class ---
 // Test that `mid` creates a Relation, but that can be overridden.

tests/suite/math/mat.typ

@@ -54,6 +54,12 @@ $ a + mat(delim: #none, 1, 2; 3, 4) + b $
   $ mat(1, 2; 3, 4; delim: "[") $,
 )
 
+--- math-mat-delim-size ---
+// Test setting delimiter size.
+$ mat(c; c; c) mat(delim-size: #100%, c; c; c) $
+#set math.mat(delim-size: x => calc.max(x - 5pt, x * 0.901))
+$ mat(delim: "[", f; f; f; f) mat(delim: ||, x; x; x; x) $
+
 --- math-mat-spread ---
 // Test argument spreading in matrix.
 $ mat(..#range(1, 5).chunks(2))

tests/suite/math/stretch.typ

@@ -91,3 +91,9 @@ $ body^"text" $
   }
   $body^"long text"$
 }
+
+--- math-stretch-function ---
+// Test using a function as an argument to size.
+$stretch(<-, size: #(x => x - 0.5em))_"function"$
+#set math.stretch(size: x => x + 0.5em)
+$stretch(|) |$

tests/suite/math/vec.typ

@@ -50,6 +50,12 @@ $ vec(1, 2) $
 // Error: 22-33 invalid delimiter: "%"
 #set math.vec(delim: (none, "%"))
 
+--- math-vec-delim-size ---
+// Test setting delimiter size.
+$ vec(1, 2, 3) vec(delim-size: #100%, 1, 2, 3) $
+#set math.vec(delim-size: x => calc.max(x - 5pt, x * 0.901))
+$ vec(delim: "{", 1, 2, 3) vec(delim: "[", 1, 2, 3) $
+
 --- math-vec-linebreaks ---
 // Warning: 20-29 linebreaks are ignored in elements
 // Hint: 20-29 use commas instead to separate each line