From 8fe8b2a23940f76077aa36eda305febd22e7cadc Mon Sep 17 00:00:00 2001
From: Max <me@mkor.je>
Date: Tue, 26 Nov 2024 20:51:22 +0000
Subject: [PATCH] Ignore leading and trailing ignorant fragments in `math.lr`
 (#5473)

---
 crates/typst-layout/src/math/lr.rs    |  22 +++++++++++++++++-----
 tests/ref/math-lr-ignore-ignorant.png | Bin 0 -> 970 bytes
 tests/suite/math/delimited.typ        |  17 +++++++++++++++++
 3 files changed, 34 insertions(+), 5 deletions(-)
 create mode 100644 tests/ref/math-lr-ignore-ignorant.png

diff --git a/crates/typst-layout/src/math/lr.rs b/crates/typst-layout/src/math/lr.rs
index aba9012f2..d195e67dc 100644
--- a/crates/typst-layout/src/math/lr.rs
+++ b/crates/typst-layout/src/math/lr.rs
@@ -28,8 +28,21 @@ pub fn layout_lr(
     }
 
     let mut fragments = ctx.layout_into_fragments(body, styles)?;
+
+    // Ignore leading and trailing ignorant fragments.
+    let start_idx = fragments
+        .iter()
+        .position(|f| !f.is_ignorant())
+        .unwrap_or(fragments.len());
+    let end_idx = fragments
+        .iter()
+        .skip(start_idx)
+        .rposition(|f| !f.is_ignorant())
+        .map_or(start_idx, |i| start_idx + i + 1);
+    let inner_fragments = &mut fragments[start_idx..end_idx];
+
     let axis = scaled!(ctx, styles, axis_height);
-    let max_extent = fragments
+    let max_extent = inner_fragments
         .iter()
         .map(|fragment| (fragment.ascent() - axis).max(fragment.descent() + axis))
         .max()
@@ -39,7 +52,7 @@ pub fn layout_lr(
     let height = elem.size(styles);
 
     // Scale up fragments at both ends.
-    match fragments.as_mut_slice() {
+    match inner_fragments {
         [one] => scale(ctx, styles, one, relative_to, height, None),
         [first, .., last] => {
             scale(ctx, styles, first, relative_to, height, Some(MathClass::Opening));
@@ -49,7 +62,7 @@ pub fn layout_lr(
     }
 
     // Handle MathFragment::Variant fragments that should be scaled up.
-    for fragment in &mut fragments {
+    for fragment in inner_fragments {
         if let MathFragment::Variant(ref mut variant) = fragment {
             if variant.mid_stretched == Some(false) {
                 variant.mid_stretched = Some(true);
@@ -60,11 +73,10 @@ pub fn layout_lr(
 
     // Remove weak SpacingFragment immediately after the opening or immediately
     // before the closing.
-    let original_len = fragments.len();
     let mut index = 0;
     fragments.retain(|fragment| {
         index += 1;
-        (index != 2 && index + 1 != original_len)
+        (index != start_idx + 2 && index + 1 != end_idx)
             || !matches!(fragment, MathFragment::Spacing(_, true))
     });
 
diff --git a/tests/ref/math-lr-ignore-ignorant.png b/tests/ref/math-lr-ignore-ignorant.png
new file mode 100644
index 0000000000000000000000000000000000000000..b82a827f59714684078d46e431f454e6a74a7830
GIT binary patch
literal 970
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zSx*yD6oCB~{sa@3#Hi7@N24)O)2O&BCayFpE{F<lpkfdgP;rF>1%+s$Yym5TNCB;E
zf`A}fDIiT`r;)a_v^~x_cV;?Qc(^edUpf!xyYtN?AGzEiOo9J&O$mep;XpVL{#)S+
zAJoU61AuZ)n*fTAXXA6N^;806tnUS|e%I>W4j4>Z4*)f8;c#^-z8`|C=NkP2e~dfn
z(nzn==&SwG2<nzb%z)q8qI}YvhpT9>VAvS}N*K~=R9%+>N*K=DRsEz1l(74(Y9Z1A
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zeZN=}9@`~b*k{v(Ypw}}3-1!D4-vj9+jp^+kno)FC|}k(FJV&`A$W*c=Vrz^4C{o#
z$EeU8dprvX%VfRWhtn8wu^ic`XLd+O$T)J#f_$98bpCamKcDPPqMg~*EfQYn;hwD+
zCAgMy78WoRMRL}3f-&kXr{ms;glF^5wzd*18x_I5m6pKSwk?bYsyUr<Pb55pf2J=Z
zl<(*DOop4!I6JtUQD^3K)&-I9bR5<K>1x2$;S#c@gE$*dTX8kZ$2KtyXBlezw1=0-
zr^$k69IX*=b0USq169&xnGm+19+(hrK<)fJ>_%J1!hf*UAs-2qdneuM+fO;$zk+c?
zJEt=*f%xGv8pnx2W<s});L82Ny_J58(3jmsY~I1NzJlH6jS!O`iiDTCa3(dUZeriD
zlQ6!R5Z4u&fb=W^x=Kz{_g=>u+L+RCrekvHVczHYgLIoC5{~#pc?(P(#llKiuXanr
zJ`KLjrN3*Zn6<CP`F;;1(HESM&9pHJ=jCJw&cwy$ev$BpI7Tb&X4Ms0$C?;l9mN@6
zEbAaQ<Iz_*x7*pBNBQdKcjDB6NZ7lL@lY$y^DVMApCt_MbRc$kWc?zCP(^!eJ0M#K
z{Xuy25~uNjP#B(?a6Yzl+5sFVRDBY6-gVv4h@E7`di6NF9s=sSP2^BqqoRTIF_&1_
zi@(47+r#m2C7M-j!BZ6+dMZr98IP)8mjaBe4i9@EAzHN%(+5zyDm<h_LMn)bp;Jnf
z84M)=1@APvFdxPZ217kSVuwa2wn3kyd%zv-^xN@E4rrFN1A1<QXc){sMrh-7tFmaH
sRQK7m)^1f^4*Xvo2nWJ}@V~fz0otu+)ZD33GXMYp07*qoM6N<$f)M(~YXATM

literal 0
HcmV?d00001

diff --git a/tests/suite/math/delimited.typ b/tests/suite/math/delimited.typ
index d6e1d8648..9e11ec8b0 100644
--- a/tests/suite/math/delimited.typ
+++ b/tests/suite/math/delimited.typ
@@ -98,6 +98,23 @@ $lr(lr(|, size: #4em), size: #50%)$
 $lr(body1, size: #50%)$
 $lr(body2, size: #50%)$
 
+--- math-lr-ignore-ignorant ---
+// Test ignoring leading and trailing ignorant fragments.
+#box($ (1 / 2) $)
+#box({
+  show "(": it => context it
+  $ (1 / 2) $
+})
+#box({
+  show ")": it => context it
+  $ (1 / 2) $
+})
+#box({
+  show "(": it => context it
+  show ")": it => context it
+  $ (1 / 2) $
+})
+
 --- issue-4188-lr-corner-brackets ---
 // Test positioning of U+231C to U+231F
 $⌜a⌟⌞b⌝$ = $⌜$$a$$⌟$$⌞$$b$$⌝$