From c3334a55fe53253b55943a4b713bff532e876d95 Mon Sep 17 00:00:00 2001
From: Max <me@mkor.je>
Date: Fri, 20 Dec 2024 10:15:18 +0000
Subject: [PATCH] Fix arbitrarily nested equations in the base of `math.attach`
 (#5613)

---
 crates/typst-layout/src/math/attach.rs        |   2 +-
 crates/typst-library/src/math/attach.rs       |   2 +-
 tests/ref/math-attach-nested-base.png         | Bin 1047 -> 1377 bytes
 tests/ref/math-attach-nested-deep-base.png    | Bin 0 -> 185 bytes
 .../math-stretch-attach-nested-equation.png   | Bin 180 -> 415 bytes
 tests/suite/math/attach.typ                   |  15 ++++++++++++++-
 tests/suite/math/stretch.typ                  |   8 ++++++++
 7 files changed, 24 insertions(+), 3 deletions(-)
 create mode 100644 tests/ref/math-attach-nested-deep-base.png

diff --git a/crates/typst-layout/src/math/attach.rs b/crates/typst-layout/src/math/attach.rs
index 0f9090f77..cda033159 100644
--- a/crates/typst-layout/src/math/attach.rs
+++ b/crates/typst-layout/src/math/attach.rs
@@ -161,7 +161,7 @@ fn stretch_size(
 ) -> Option<Smart<Rel<Length>>> {
     // Extract from an EquationElem.
     let mut base = elem.base();
-    if let Some(equation) = base.to_packed::<EquationElem>() {
+    while let Some(equation) = base.to_packed::<EquationElem>() {
         base = equation.body();
     }
 
diff --git a/crates/typst-library/src/math/attach.rs b/crates/typst-library/src/math/attach.rs
index 74eabd101..f3c7ea99f 100644
--- a/crates/typst-library/src/math/attach.rs
+++ b/crates/typst-library/src/math/attach.rs
@@ -48,7 +48,7 @@ impl Packed<AttachElem> {
     pub fn merge_base(&self) -> Option<Self> {
         // Extract from an EquationElem.
         let mut base = self.base();
-        if let Some(equation) = base.to_packed::<EquationElem>() {
+        while let Some(equation) = base.to_packed::<EquationElem>() {
             base = equation.body();
         }
 
diff --git a/tests/ref/math-attach-nested-base.png b/tests/ref/math-attach-nested-base.png
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diff --git a/tests/ref/math-attach-nested-deep-base.png b/tests/ref/math-attach-nested-deep-base.png
new file mode 100644
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diff --git a/tests/ref/math-stretch-attach-nested-equation.png b/tests/ref/math-stretch-attach-nested-equation.png
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GIT binary patch
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diff --git a/tests/suite/math/attach.typ b/tests/suite/math/attach.typ
index 56fa47c58..cedc3a4ab 100644
--- a/tests/suite/math/attach.typ
+++ b/tests/suite/math/attach.typ
@@ -167,9 +167,22 @@ $ attach(a^b, b: c) quad
 
 #let a0 = math.attach(math.alpha, b: [0])
 #let a1 = $alpha^1$
+#let a2 = $attach(a1, bl: 3)$
 
 $ a0 + a1 + a0_2 \
-  a1_2 + a0^2 + a1^2 $
+  a1_2 + a0^2 + a1^2 \
+  a2 + a2_2 + a2^2 $
+
+--- math-attach-nested-deep-base ---
+// Test attachments when the base has attachments and is nested arbitrarily
+// deep.
+#{
+  let var = $x^1$
+  for i in range(24) {
+    var = $var$    
+  }
+  $var_2$
+}
 
 --- math-attach-scripts-extended-shapes ---
 // Test script attachments positioning if the base is an extended shape (or a
diff --git a/tests/suite/math/stretch.typ b/tests/suite/math/stretch.typ
index 6bf13e255..1377f4d21 100644
--- a/tests/suite/math/stretch.typ
+++ b/tests/suite/math/stretch.typ
@@ -83,3 +83,11 @@ $ stretch(base, size: #50%) $
 // Test stretching with attachments when nested in an equation.
 #let body = $stretch(=)$
 $ body^"text" $
+
+#{
+  let body = $stretch(=)$
+  for i in range(24) {
+    body = $body$    
+  }
+  $body^"long text"$
+}