Optimize: remove every page's reference to a shared link left with no action

A link annotation listed twice in one page's /Annots, or by two pages, kept its later references after the first one stripped its external action, leaving inert links on the page. Every reference to a link that ends up with no action and no /Dest is now removed. A shared link counts once in external_links.

crates/optimize/src/external_refs.rs

@@ -373,6 +373,7 @@ fn discard_bookmarks(doc: &mut Document) -> Result<usize, OptimizeError> {
 /// changed; a link counts whether it was removed or kept for its other actions.
 pub(crate) fn discard(doc: &mut Document, pages: &[ObjRef]) -> Result<(usize, usize), OptimizeError> {
     let mut links = 0;
+    let mut removed_links = HashSet::new();
     for p in pages {
         let Some(pd) = doc.get(*p).as_dict().cloned() else { continue };
         let Some(annots) = pd.get(b"Annots").map(|a| doc.resolve(a)).and_then(|a| a.as_array().cloned()) else { continue };
@@ -393,7 +394,11 @@ pub(crate) fn discard(doc: &mut Document, pages: &[ObjRef]) -> Result<(usize, us
                 _ => None,
             };
             let Some(action) = stripped else {
-                keep.push(x.clone());
+                if !matches!(x, Object::Ref(r) if removed_links.contains(r)) {
+                    keep.push(x.clone());
+                } else {
+                    changed = true;
+                }
                 continue;
             };
             links += 1;
@@ -408,6 +413,7 @@ pub(crate) fn discard(doc: &mut Document, pages: &[ObjRef]) -> Result<(usize, us
                 Object::Ref(r) => {
                     doc.set(*r, Object::Dict(d));
                     if removed {
+                        removed_links.insert(*r);
                         changed = true;
                     } else {
                         keep.push(x.clone());

crates/optimize/tests/optimize.rs

@@ -2436,6 +2436,38 @@ fn links_and_bookmarks_to_other_documents_are_discarded_and_links_within_stay()
     assert_eq!(chain(&doc, bookmark(&doc, items[1]).get(b"A").unwrap()), ["Named"]);
 }
 
+#[test]
+fn repeated_indirect_remote_link_is_removed_from_one_page() {
+    let (mut doc, p, _) = linked_doc(
+        |doc, _| {
+            let link = doc.add(link_with(Some(action("GoToR", None)), None));
+            vec![Object::Ref(link), Object::Ref(link)]
+        },
+        &[],
+    );
+    let report = optimize(&mut doc, &Settings { discard_external_refs: true, ..Settings::default() }).unwrap();
+    assert_eq!(report.external_links, 1, "{report:?}");
+    assert!(annots_of(&doc, p).is_empty(), "both references leave the page");
+}
+
+#[test]
+fn shared_indirect_remote_link_with_empty_next_is_removed_from_every_page() {
+    let (mut doc, first, items) = linked_doc(|_, _| Vec::new(), &[action("Named", None), action("GoToR", None)]);
+    let second = page(&mut doc, &[], "BT ET");
+    let link = doc.add(link_with(Some(action("GoToR", Some(Object::Array(vec![Object::Null])))), None));
+    for p in [first, second] {
+        doc.update_dict(p, |d| d.set(b"Annots".to_vec(), Object::Array(vec![Object::Ref(link)]))).unwrap();
+    }
+    doc.update_dict(items[0], |d| d.set(b"First".to_vec(), Object::Ref(items[1]))).unwrap();
+    let report = optimize(&mut doc, &Settings { discard_external_refs: true, ..Settings::default() }).unwrap();
+    assert_eq!(report.external_links, 1, "{report:?}");
+    assert_eq!(report.external_bookmarks, 1, "{report:?}");
+    assert!(doc.get(items[1]).as_dict().unwrap().get(b"A").is_none(), "the shared bookmark has no action");
+    assert!(annots_of(&doc, first).is_empty(), "the first page loses the link");
+    assert!(annots_of(&doc, second).is_empty(), "the second page loses the link");
+    assert!(doc.get(link).as_dict().unwrap().get(b"A").is_none(), "the shared link has no action");
+}
+
 #[test]
 fn an_action_to_another_document_hands_its_place_to_the_actions_after_it() {
     let (doc, p, _) = linked_doc(