chore: backport hashmap fix

Author: mikearnaldi

packages/system/src/Collections/Immutable/HashMap/Nodes/index.ts

@@ -199,30 +199,35 @@ export class IndexedNode<K, V> {
     const bit = toBitmap(frag)
     const indx = fromBitmap(mask, bit)
     const exists = mask & bit
+    const canEdit = canEditNode(edit, this)
+
+    if (!exists) {
+      const _newChild = new Empty<K, V>().modify(edit, shift + SIZE, f, hash, key, size)
+      if (!_newChild) return this
+      return children.length >= MAX_INDEX_NODE
+        ? expand(edit, frag, _newChild, mask, children)
+        : new IndexedNode(
+            edit,
+            mask | bit,
+            arraySpliceIn(canEdit, indx, _newChild, children)
+          )
+    }
+
     const current = exists ? children[indx]! : new Empty<K, V>()
     const child = current.modify(edit, shift + SIZE, f, hash, key, size)
 
     if (current === child) return this
 
-    const canEdit = canEditNode(edit, this)
     let bitmap = mask
     let newChildren
-    if (exists && isEmptyNode(child)) {
+    if (isEmptyNode(child)) {
       // remove
       bitmap &= ~bit
       if (!bitmap) return new Empty()
       if (children.length <= 2 && isLeaf(children[indx ^ 1]!))
         return children[indx ^ 1]! // collapse
 
       newChildren = arraySpliceOut(canEdit, indx, children)
-    } else if (!exists && !isEmptyNode(child)) {
-      // add
-      if (children.length >= MAX_INDEX_NODE) {
-        return expand(edit, frag, child, mask, children)
-      }
-
-      bitmap |= bit
-      newChildren = arraySpliceIn(canEdit, indx, child, children)
     } else {
       // modify
       newChildren = arrayUpdate(canEdit, indx, child, children)
@@ -233,6 +238,7 @@ export class IndexedNode<K, V> {
       this.children = newChildren
       return this
     }
+
     return new IndexedNode(edit, bitmap, newChildren)
   }
 }