Compose: span columns in a one-column frame add no span space

crates/compose/src/lib.rs

@@ -805,6 +805,9 @@ fn compose_with_db(doc: &Document, story: &Story, frames: &[FrameSpec], opts: &C
         // the next column.
         let spanning = matches!(pp.span_columns, SpanColumns::Span(n) if n != 1);
         span_paras[pi] = spanning;
+        // Span space applies where the paragraph spans more than one column; in a one-column frame
+        // a span changes nothing.
+        let spans_in = |fi: usize| spanning && cols.get(fi).is_some_and(|c| c.len() > 1);
         // Consecutive paragraphs with the same Split Columns settings share a split block; within
         // it, a paragraph moves on to the next sub-column.
         let split_cfg = SplitCfg::of(&pp);
@@ -877,7 +880,7 @@ fn compose_with_db(doc: &Document, story: &Story, frames: &[FrameSpec], opts: &C
                 cur.col = 0;
                 cur.last_baseline = Some(baseline);
                 cur.last_descent = descent;
-                text_above = true;
+                text_above = multi;
             } else if cur.col != 0 {
                 cur.col = 0;
                 cur.resume();
@@ -1164,7 +1167,7 @@ fn compose_with_db(doc: &Document, story: &Story, frames: &[FrameSpec], opts: &C
                 baseline: l.baseline,
                 descent: l.descent,
                 reference: cur.last_reference,
-                pending: pp.space_after.max(pp.span_space_after),
+                pending: if spans_in(cur.fi) { pp.space_after.max(pp.span_space_after) } else { pp.space_after },
             };
             cur.band = Band { para: pi + 1, line0: ft.lines.len(), above: Some(above) };
         }
@@ -1245,7 +1248,7 @@ fn compose_with_db(doc: &Document, story: &Story, frames: &[FrameSpec], opts: &C
                 }
             }
         }
-        cur.pending += if spanning || ends_split { pp.space_after.max(pp.span_space_after) } else { pp.space_after };
+        cur.pending += if spans_in(cur.fi) || ends_split { pp.space_after.max(pp.span_space_after) } else { pp.space_after };
         pi += 1;
     }
     notes.finish(doc, story, frames, &cols, &mut out);

crates/compose/src/tests.rs

@@ -2896,6 +2896,29 @@ fn space_before_and_after_a_span_moves_the_span_and_the_text_below() {
     assert!((span2 - span0).abs() < 0.01 && (below2 - below0 - 18.0).abs() < 0.01, "{below0} → {below2}");
 }
 
+#[test]
+fn span_space_applies_only_where_the_paragraph_spans_columns() {
+    // Every paragraph spans with 12 pt span space after; the frame has `columns` columns.
+    let tops = |columns: u32, span: bool| {
+        let (mut d, sid, fid) = doc_with("One\nTwo\nThree", Rect::new(0.0, 0.0, 400.0, 400.0), ParaAttrs::default());
+        d.item_mut(fid).unwrap().text_frame_mut().unwrap().options.columns = columns;
+        for p in &mut d.story_mut(sid).unwrap().paras {
+            if span {
+                p.para.span_columns = Some(SpanColumns::Span(0));
+            }
+            p.para.span_space_after = Some(12.0);
+        }
+        let cs = compose_story(&d, sid, &ComposeOptions::default());
+        first_lines(&cs).iter().map(|l| l.baseline).collect::<Vec<_>>()
+    };
+    let plain = tops(1, false);
+    assert_eq!(plain.len(), 3);
+    assert_eq!(tops(1, true), plain, "a span in a one-column frame adds no space");
+    let spread = tops(3, true);
+    let gap = |v: &[f64], i: usize| v[i + 1] - v[i];
+    assert!((gap(&spread, 0) - gap(&plain, 0) - 12.0).abs() < 0.01, "{spread:?} vs {plain:?}");
+}
+
 /// The first line of each paragraph.
 fn first_lines(cs: &ComposedStory) -> Vec<&Line> {
     all_lines(cs).into_iter().filter(|l| l.first_in_para).collect()