fix(format): import a Sketch page once however often the file lists it (#1973)

crates/format/src/sketch.rs

@@ -226,11 +226,16 @@ impl<'b> Archive<'b> {
         };
         let refs = document.get("pages").and_then(Value::as_array).map(Vec::as_slice).unwrap_or_default();
         let mut pages = Vec::new();
+        let mut seen = std::collections::HashSet::new();
         for r in refs.iter().take(MAX_PAGES) {
             let Some(id) = r.get("_ref").and_then(Value::as_str).and_then(|s| s.strip_prefix("pages/")).filter(|id| valid_id(id)) else {
                 warnings.push("pages the document lists without a valid reference were skipped".into());
                 continue;
             };
+            // A page listed twice is read once: a repeated reference must not repeat the unpacking.
+            if !seen.insert(id) {
+                continue;
+            }
             match json_member(&mut z, &format!("pages/{id}.json"), max_member, &mut total) {
                 Ok(page) if page.is_object() => pages.push((id.to_string(), page)),
                 Ok(_) => warnings.push("pages that aren't JSON objects were skipped".into()),

crates/format/src/sketch/tests.rs

@@ -35,6 +35,13 @@ fn pages_become_pages_in_document_order() {
     assert_eq!(page_names(&doc), ["Beta", "Alpha"]);
 }
 
+#[test]
+fn a_page_listed_twice_is_imported_once() {
+    let z = sketch_zip("50.2", 103, document(&["A", "A", "A"]), &[page("A", "Alpha", vec![])], &[]);
+    let (doc, _) = import(&z, "f").unwrap();
+    assert_eq!(page_names(&doc), ["Alpha"]);
+}
+
 #[test]
 fn older_than_48_is_refused() {
     let z = sketch_zip("47.1", 95, document(&["P"]), &[page("P", "P", vec![])], &[]);