Fix breakable block equation overflow (#5078)

4 files changed, 18 insertions, 3 deletions

diff --git a/crates/typst/src/math/equation.rs b/crates/typst/src/math/equation.rs
index bf5ef9dd..dfcb0f7b 100644
--- a/crates/typst/src/math/equation.rs
+++ b/crates/typst/src/math/equation.rs
@@ -322,10 +322,8 @@ fn layout_equation_block(
         .layout_into_run(&elem.body, styles)?
         .multiline_frame_builder(&ctx, styles);
     let width = full_equation_builder.size.x;
-    let can_break =
-        BlockElem::breakable_in(styles) && full_equation_builder.frames.len() > 1;
 
-    let equation_builders = if can_break {
+    let equation_builders = if BlockElem::breakable_in(styles) {
         let mut rows = full_equation_builder.frames.into_iter().peekable();
         let mut equation_builders = vec![];
         let mut last_first_pos = Point::zero();
diff --git a/tests/ref/math-pagebreaking-single-line-numbered.png b/tests/ref/math-pagebreaking-single-line-numbered.png
new file mode 100644
index 00000000..4e5b93eb
--- /dev/null
+++ b/tests/ref/math-pagebreaking-single-line-numbered.png
diff --git a/tests/ref/math-pagebreaking-single-line.png b/tests/ref/math-pagebreaking-single-line.png
new file mode 100644
index 00000000..877d9c8b
--- /dev/null
+++ b/tests/ref/math-pagebreaking-single-line.png
diff --git a/tests/suite/math/multiline.typ b/tests/suite/math/multiline.typ
index 8377b93e..3c0ed2f4 100644
--- a/tests/suite/math/multiline.typ
+++ b/tests/suite/math/multiline.typ
@@ -130,6 +130,23 @@ $ a &+ b + & c \
     &      & c && + d \
     &= 0 $
 
+--- math-pagebreaking-single-line ---
+// Test breaking of single line equations.
+#set page(height: 4em)
+#show math.equation: set block(breakable: true)
+
+Shouldn't overflow:
+$ a + b $
+
+--- math-pagebreaking-single-line-numbered ---
+// Test breaking of single line equations with numbering.
+#set page(height: 4em)
+#show math.equation: set block(breakable: true)
+#set math.equation(numbering: "(1)")
+
+Shouldn't overflow:
+$ a + b $
+
 --- issue-1948-math-text-break ---
 // Test text with linebreaks in math.
 $ x := "a\nb\nc\nd\ne" $