Fix box in 100% width block

Fixes #2128

crates/typst-library/src/layout/mod.rs

@@ -266,6 +266,7 @@ fn realize_block<'a>(
     // These elements implement `Layout` but still require a flow for
     // proper layout.
     if content.can::<dyn Layout>()
+        && !content.is::<BoxElem>()
         && !content.is::<LineElem>()
         && !content.is::<RectElem>()
         && !content.is::<SquareElem>()

crates/typst-library/src/math/ctx.rs

@@ -149,6 +149,12 @@ impl<'a, 'b, 'v> MathContext<'a, 'b, 'v> {
         Ok(self.layout_fragment(elem)?.into_frame())
     }
 
+    pub fn layout_box(&mut self, boxed: &BoxElem) -> SourceResult<Frame> {
+        Ok(boxed
+            .layout(self.vt, self.outer.chain(&self.local), self.regions)?
+            .into_frame())
+    }
+
     pub fn layout_content(&mut self, content: &Content) -> SourceResult<Frame> {
         Ok(content
             .layout(self.vt, self.outer.chain(&self.local), self.regions)?

crates/typst-library/src/math/mod.rs

@@ -457,18 +457,20 @@ impl LayoutMath for Content {
             return Ok(());
         }
 
+        if let Some(boxed) = self.to::<BoxElem>() {
+            let frame = ctx.layout_box(boxed)?;
+            ctx.push(FrameFragment::new(ctx, frame).with_spaced(true));
+            return Ok(());
+        }
+
         if let Some(elem) = self.with::<dyn LayoutMath>() {
             return elem.layout_math(ctx);
         }
 
         let mut frame = ctx.layout_content(self)?;
         if !frame.has_baseline() {
-            if self.is::<BoxElem>() {
-                frame.set_baseline(frame.height());
-            } else {
-                let axis = scaled!(ctx, axis_height);
-                frame.set_baseline(frame.height() / 2.0 + axis);
-            }
+            let axis = scaled!(ctx, axis_height);
+            frame.set_baseline(frame.height() / 2.0 + axis);
         }
         ctx.push(FrameFragment::new(ctx, frame).with_spaced(true));
 

tests/typ/bugs/block-width-box.typ

@@ -0,0 +1,6 @@
+// Test box in 100% width block.
+
+---
+#block(width: 100%, fill: red, box("a box"))
+
+#block(width: 100%, fill: red, [#box("a box") #box()])