fix(array): track correct changes when setting nested array of primitives

lib/schema/array.js

@@ -359,7 +359,11 @@ SchemaArray.prototype.cast = function(value, doc, init, prev, options) {
     options = options || emptyOpts;
 
     let rawValue = utils.isMongooseArray(value) ? value.__array : value;
-    value = MongooseArray(rawValue, options.path || this._arrayPath || this.path, doc, this);
+    let path = options.path || this.path;
+    if (options.arrayPathIndex != null) {
+      path += '.' + options.arrayPathIndex;
+    }
+    value = MongooseArray(rawValue, path, doc, this);
     rawValue = value.__array;
 
     if (init && doc != null && doc.$__ != null && doc.$populated(this.path)) {

test/schema.test.js

@@ -2562,7 +2562,7 @@ describe('schema', function() {
     });
 
     const casted = schema.path('ids').cast([[]]);
-    assert.equal(casted[0].$path(), 'ids.$');
+    assert.equal(casted[0].$path(), 'ids.0');
   });
 
   describe('cast option (gh-8407)', function() {

test/types.array.test.js

@@ -1899,4 +1899,20 @@ describe('types array', function() {
 
     m.Schema.Types.Array.options.castNonArrays = true;
   });
+
+  it('supports setting nested arrays directly (gh-13372)', function() {
+    const Test = db.model('Test', new Schema({ intArr: [[Number]] }));
+
+    const intArr = [[1, 2], [3, 4]];
+    const doc = Test.hydrate({ intArr });
+
+    doc.intArr[0][0] = 2;
+    doc.intArr[1][1] = 5;
+    assert.deepStrictEqual(doc.getChanges(), {
+      $set: {
+        'intArr.0.0': 2,
+        'intArr.1.1': 5
+      }
+    });
+  });
 });