Add span information to realized ParElem (#2675)

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

@@ -637,7 +637,15 @@ impl<'a> ParBuilder<'a> {
 
     fn finish(self) -> (Content, StyleChain<'a>) {
         let (children, shared) = self.0.finish();
-        (ParElem::new(children.to_vec()).pack(), shared)
+
+        // Find the first span that isn't detached.
+        let span = children
+            .iter()
+            .map(|(cnt, _)| cnt.span())
+            .find(|span| !span.is_detached())
+            .unwrap_or_else(Span::detached);
+
+        (ParElem::new(children.to_vec()).spanned(span).pack(), shared)
     }
 }
 

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

@@ -252,7 +252,9 @@ impl<'a, 'b, 'v> MathContext<'a, 'b, 'v> {
         // because it will be placed somewhere probably not at the left margin
         // it will overflow.  So emulate an `hbox` instead and allow the paragraph
         // to extend as far as needed.
+        let span = elem.span();
         let frame = ParElem::new(vec![Prehashed::new(elem)])
+            .spanned(span)
             .layout(
                 self.vt,
                 self.outer.chain(&self.local),