Created new system for limits (fixes #1443) (#1452)

library/src/math/attach.rs

@@ -77,18 +77,9 @@ impl LayoutMath for AttachElem {
         let b = layout_attachment(ctx, Self::b)?;
         ctx.unstyle();
 
-        let as_limits = self.base().is::<LimitsElem>()
-            || (!self.base().is::<ScriptsElem>()
-                && ctx.style.size == MathSize::Display
-                && base.class() == Some(MathClass::Large)
-                && match &base {
-                    MathFragment::Variant(variant) => LIMITS.contains(&variant.c),
-                    MathFragment::Frame(fragment) => fragment.limits,
-                    _ => false,
-                });
-
-        let (t, tr) = if as_limits || tr.is_some() { (t, tr) } else { (None, t) };
-        let (b, br) = if as_limits || br.is_some() { (b, br) } else { (None, b) };
+        let limits = base.limits().active(ctx);
+        let (t, tr) = if limits || tr.is_some() { (t, tr) } else { (None, t) };
+        let (b, br) = if limits || br.is_some() { (b, br) } else { (None, b) };
         layout_attachments(ctx, base, [tl, t, tr, bl, b, br])
     }
 }
@@ -112,7 +103,10 @@ pub struct ScriptsElem {
 impl LayoutMath for ScriptsElem {
     #[tracing::instrument(skip(ctx))]
     fn layout_math(&self, ctx: &mut MathContext) -> SourceResult<()> {
-        self.body().layout_math(ctx)
+        let mut fragment = ctx.layout_fragment(&self.body())?;
+        fragment.set_limits(Limits::Never);
+        ctx.push(fragment);
+        Ok(())
     }
 }
 
@@ -135,10 +129,56 @@ pub struct LimitsElem {
 impl LayoutMath for LimitsElem {
     #[tracing::instrument(skip(ctx))]
     fn layout_math(&self, ctx: &mut MathContext) -> SourceResult<()> {
-        self.body().layout_math(ctx)
+        let mut fragment = ctx.layout_fragment(&self.body())?;
+        fragment.set_limits(Limits::Always);
+        ctx.push(fragment);
+        Ok(())
     }
 }
 
+/// Describes in which situation a frame should use limits for attachments.
+#[derive(Debug, Copy, Clone)]
+pub enum Limits {
+    /// Always scripts.
+    Never,
+    /// Display limits only in `display` math.
+    Display,
+    /// Always limits.
+    Always,
+}
+
+impl Limits {
+    /// The default limit configuration if the given character is the base.
+    pub fn for_char(c: char) -> Self {
+        if Self::DEFAULT_TO_LIMITS.contains(&c) {
+            Limits::Display
+        } else {
+            Limits::Never
+        }
+    }
+
+    /// Whether limits should be displayed in this context
+    pub fn active(&self, ctx: &MathContext) -> bool {
+        match self {
+            Self::Always => true,
+            Self::Display => ctx.style.size == MathSize::Display,
+            Self::Never => false,
+        }
+    }
+
+    /// Unicode codepoints that should show attachments as limits in display
+    /// mode.
+    #[rustfmt::skip]
+    const DEFAULT_TO_LIMITS: &[char] = &[
+        /* ∏ */ '\u{220F}', /* ∐ */ '\u{2210}', /* ∑ */ '\u{2211}',
+        /* ⋀ */ '\u{22C0}', /* ⋁ */ '\u{22C1}',
+        /* ⋂ */ '\u{22C2}', /* ⋃ */ '\u{22C3}',
+        /* ⨀ */ '\u{2A00}', /* ⨁ */ '\u{2A01}', /* ⨂ */ '\u{2A02}',
+        /* ⨃ */ '\u{2A03}', /* ⨄ */ '\u{2A04}',
+        /* ⨅ */ '\u{2A05}', /* ⨆ */ '\u{2A06}',
+    ];
+}
+
 macro_rules! measure {
     ($e: ident, $attr: ident) => {
         $e.as_ref().map(|e| e.$attr()).unwrap_or_default()
@@ -358,14 +398,3 @@ fn is_atomic_text_frame(frame: &Frame) -> bool {
         .filter(|item| !matches!(item, FrameItem::Meta(_, _)));
     matches!(iter.next(), Some(FrameItem::Text(_))) && iter.next().is_none()
 }
-
-/// Unicode codepoints that should have sub- and superscripts attached as limits.
-#[rustfmt::skip]
-const LIMITS: &[char] = &[
-    /* ∏ */ '\u{220F}', /* ∐ */ '\u{2210}', /* ∑ */ '\u{2211}',
-    /* ⋀ */ '\u{22C0}', /* ⋁ */ '\u{22C1}',
-    /* ⋂ */ '\u{22C2}', /* ⋃ */ '\u{22C3}',
-    /* ⨀ */ '\u{2A00}', /* ⨁ */ '\u{2A01}', /* ⨂ */ '\u{2A02}',
-    /* ⨃ */ '\u{2A03}', /* ⨄ */ '\u{2A04}',
-    /* ⨅ */ '\u{2A05}', /* ⨆ */ '\u{2A06}',
-];

library/src/math/fragment.rs

@@ -90,6 +90,15 @@ impl MathFragment {
         }
     }
 
+    pub fn set_limits(&mut self, limits: Limits) {
+        match self {
+            Self::Glyph(glyph) => glyph.limits = limits,
+            Self::Variant(variant) => variant.limits = limits,
+            Self::Frame(fragment) => fragment.limits = limits,
+            _ => {}
+        }
+    }
+
     pub fn is_spaced(&self) -> bool {
         match self {
             MathFragment::Frame(frame) => frame.spaced,
@@ -113,6 +122,15 @@ impl MathFragment {
             _ => Frame::new(self.size()),
         }
     }
+
+    pub fn limits(&self) -> Limits {
+        match self {
+            MathFragment::Glyph(glyph) => glyph.limits,
+            MathFragment::Variant(variant) => variant.limits,
+            MathFragment::Frame(fragment) => fragment.limits,
+            _ => Limits::Never,
+        }
+    }
 }
 
 impl From<GlyphFragment> for MathFragment {
@@ -149,6 +167,7 @@ pub struct GlyphFragment {
     pub class: Option<MathClass>,
     pub span: Span,
     pub meta: Vec<Meta>,
+    pub limits: Limits,
 }
 
 impl GlyphFragment {
@@ -164,6 +183,10 @@ impl GlyphFragment {
     }
 
     pub fn with_id(ctx: &MathContext, c: char, id: GlyphId, span: Span) -> Self {
+        let class = match c {
+            ':' => Some(MathClass::Relation),
+            _ => unicode_math_class::class(c),
+        };
         let mut fragment = Self {
             id,
             c,
@@ -175,11 +198,9 @@ impl GlyphFragment {
             width: Abs::zero(),
             ascent: Abs::zero(),
             descent: Abs::zero(),
+            limits: Limits::for_char(c),
             italics_correction: Abs::zero(),
-            class: match c {
-                ':' => Some(MathClass::Relation),
-                _ => unicode_math_class::class(c),
-            },
+            class,
             span,
             meta: MetaElem::data_in(ctx.styles()),
         };
@@ -224,6 +245,7 @@ impl GlyphFragment {
             italics_correction: self.italics_correction,
             class: self.class,
             span: self.span,
+            limits: self.limits,
             frame: self.into_frame(),
         }
     }
@@ -268,6 +290,7 @@ pub struct VariantFragment {
     pub font_size: Abs,
     pub class: Option<MathClass>,
     pub span: Span,
+    pub limits: Limits,
 }
 
 impl Debug for VariantFragment {
@@ -282,7 +305,7 @@ pub struct FrameFragment {
     pub style: MathStyle,
     pub font_size: Abs,
     pub class: MathClass,
-    pub limits: bool,
+    pub limits: Limits,
     pub spaced: bool,
     pub base_ascent: Abs,
 }
@@ -296,7 +319,7 @@ impl FrameFragment {
             font_size: ctx.size,
             style: ctx.style,
             class: MathClass::Normal,
-            limits: false,
+            limits: Limits::Never,
             spaced: false,
             base_ascent,
         }
@@ -306,7 +329,7 @@ impl FrameFragment {
         Self { class, ..self }
     }
 
-    pub fn with_limits(self, limits: bool) -> Self {
+    pub fn with_limits(self, limits: Limits) -> Self {
         Self { limits, ..self }
     }
 

library/src/math/op.rs

@@ -26,7 +26,7 @@ pub struct OpElem {
     #[required]
     pub text: EcoString,
 
-    /// Whether the operator should force attachments to display as limits.
+    /// Whether the operator should show attachments as limits in display mode.
     #[default(false)]
     pub limits: bool,
 }
@@ -39,7 +39,11 @@ impl LayoutMath for OpElem {
         ctx.push(
             FrameFragment::new(ctx, fragment.into_frame())
                 .with_class(MathClass::Large)
-                .with_limits(self.limits(ctx.styles())),
+                .with_limits(if self.limits(ctx.styles()) {
+                    Limits::Display
+                } else {
+                    Limits::Never
+                }),
         );
         Ok(())
     }

library/src/math/stretch.rs

@@ -185,6 +185,7 @@ fn assemble(
         italics_correction: Abs::zero(),
         class: base.class,
         span: base.span,
+        limits: base.limits,
     }
 }
 

tests/typ/math/attach.typ

@@ -91,3 +91,11 @@ $ limits(integral)_a^b != integral_a^b $
 ---
 // Error: 30-34 unknown variable: oops
 $ attach(A, t: #locate(it => oops)) $
+
+---
+// Show and let rules for limits and scripts
+#let eq = $ ∫_a^b iota_a^b $
+#eq
+#show "∫": math.limits
+#show math.iota: math.limits
+#eq