fix diff issue

Author: dmonad

src/delta/delta.js

@@ -1174,10 +1174,12 @@ export const slice = (d, start = 0, end = d.childCnt, currNode = d.children.star
   }
   while (currNode != null && currNode.length <= remainingLen) {
     list.pushEnd(cpy.children, currNode.clone())
+    remainingLen -= currNode.length
     currNode = currNode.next
   }
   if (currNode != null && remainingLen > 0) {
     list.pushEnd(cpy.children, currNode.clone(0, remainingLen))
+    remainingLen -= math.min(currNode.length, remainingLen)
   }
   cpy.childCnt = slicedLen - remainingLen
   // @ts-ignore
@@ -1621,7 +1623,7 @@ export class DeltaBuilder extends Delta {
             remainingLen -= delLen
           }
         }
-      } else if ($modifyAttrOp.check(op)) {
+      } else if ($modifyOp.check(op)) {
         if (opsI == null) {
           list.pushEnd(this.children, op.clone())
           this.childCnt += 1

src/delta/delta.test.js

@@ -791,3 +791,13 @@ export const testDeltaTypings = () => {
 /**
  * @typedef {IsDeltaOpAny<delta.DeleteOp<{text:true}>>} DeltaOpTestAnyDeleteOp2
  */
+
+export const testDeltaDiffIssue1 = () => {
+  const stateA = delta.create().insert([delta.create('paragraph').setAttr('ychange', null).insert('ABCDEFGHIJKLMNOPQRSTUVWXYZ')])
+  const stateB = delta.create().insert([delta.create('paragraph').setAttr('ychange', null).insert('ABCDE123FGHIJKLMNOPQRSTUVWXYZ2sawfa')])
+  const expectedDiff = delta.create().modify(delta.create().retain(5).insert('123').retain(21).insert('2sawfa'))
+  const diffResult = delta.diff(stateA, stateB)
+  const synced = delta.clone(stateA).apply(diffResult)
+  t.assert(synced.equals(stateB))
+  t.assert(expectedDiff.equals(diffResult))
+}