Try LinkedHashMap instead of IndexMap

dpx/Cargo.toml

@@ -15,7 +15,7 @@ md-5 = "0.8.0"
 sha2 = "0.8.0"
 rand = "0.7.2"
 chrono = "0.4.9"
-indexmap = "1.3.0"
+linked-hash-map = "0.5.2"
 
 [features]
 default = ['libz-sys']

dpx/src/dpx_pdfobj.rs

@@ -222,12 +222,12 @@ pub struct xref_entry {
     pub indirect: PdfObjRef,
 }
 
-use indexmap::IndexMap;
+use linked_hash_map::LinkedHashMap;
 
 #[derive(Clone)]
 #[repr(C)]
 pub struct PdfDict {
-    inner: IndexMap<PdfName, PdfObjRef>,
+    inner: LinkedHashMap<PdfName, PdfObjRef>,
 }
 
 impl PdfDict {
@@ -1186,15 +1186,15 @@ unsafe fn write_dict(dict: &PdfDict, handle: &mut OutputHandleWrapper) {
 pub fn pdf_new_dict() -> PdfObjRef {
     safe_new_obj(PdfObjType::DICT, |object| {
         let boxed = Box::new(PdfDict {
-            inner: IndexMap::new(),
+            inner: LinkedHashMap::new(),
         });
         object.data = Box::into_raw(boxed) as *mut libc::c_void;
     })
 }
 
 unsafe fn release_dict(mut data: *mut PdfDict) {
     let mut boxed = Box::from_raw(data);
-    for (_k, v) in boxed.inner.drain(..) {
+    for (_k, &v) in boxed.inner.iter() {
         unsafe {
             pdf_release_obj(v);
         }
@@ -1228,12 +1228,12 @@ pub unsafe extern "C" fn pdf_merge_dict(dict1: &mut pdf_obj, dict2: &pdf_obj) {
     let dict2 = dict2.get_dict();
     for (k, &v) in dict2.inner.iter() {
         let linked = pdf_link_obj(v);
-        dict1.inner.entry(k.clone())
-            .and_modify(|existing| {
-                let existing = mem::replace(existing, linked);
-                pdf_release_obj(existing);
-            })
-            .or_insert(linked);
+        if let Some(existing) = dict1.inner.get_mut(k) {
+            let existing = mem::replace(existing, linked);
+            pdf_release_obj(existing);
+        } else {
+            dict1.inner.insert(k.clone(), linked);
+        }
     }
 }