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

1 files changed, 54 insertions, 25 deletions

diff --git a/library/src/math/attach.rs b/library/src/math/attach.rs
index cbf083c0..eee1e80e 100644
--- a/library/src/math/attach.rs
+++ b/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}',
-];