Fixed update children problem with xml

examples/data1.yaml

@@ -1,3 +1,2 @@
-{name: Mike}
----
-{name: Bob}
+- cat
+- dog

examples/mike.xml

@@ -1 +1 @@
-<cat>3</cat>
+<zoo><thing><frog>boing</frog></thing></zoo>

pkg/yqlib/doc/usage/xml.md

@@ -129,21 +129,20 @@ zoo:
 ```
 
 ## Parse xml: force all as an array
-Because of the way yq works, when updating everything you need to update the children before the parents. By default `..` will match parents first, so we reverse that before updating.
-
 Given a sample.xml file of:
 ```xml
 <zoo><thing><frog>boing</frog></thing></zoo>
 ```
 then
 ```bash
-yq -oy '([..] | reverse | .[]) |= [] + .' sample.xml
+yq -oy '.. |= [] + .' sample.xml
 ```
 will output
 ```yaml
-zoo:
-  thing:
-    frog: boing
+- zoo:
+    - thing:
+        - frog:
+            - boing
 ```
 
 ## Parse xml: attributes

pkg/yqlib/operator_assign.go

@@ -45,7 +45,11 @@ func assignUpdateOperator(d *dataTreeNavigator, context Context, expressionNode
 		return context, err
 	}
 
-	for el := lhs.MatchingNodes.Front(); el != nil; el = el.Next() {
+	//traverse backwards through the context -
+	// like delete, we need to run against the children first.
+	// (e.g. consider when running with expression '.. |= [.]' - we need
+	// to wrap the children first
+	for el := lhs.MatchingNodes.Back(); el != nil; el = el.Prev() {
 		candidate := el.Value.(*CandidateNode)
 
 		rhs, err := d.GetMatchingNodes(context.SingleChildContext(candidate), expressionNode.RHS)

pkg/yqlib/xml_test.go

@@ -364,11 +364,10 @@ var xmlScenarios = []formatScenario{
 		expected:       "zoo:\n    animal:\n        - cat\n",
 	},
 	{
-		description:    "Parse xml: force all as an array",
-		subdescription: "Because of the way yq works, when updating everything you need to update the children before the parents. By default `..` will match parents first, so we reverse that before updating.",
-		input:          "<zoo><thing><frog>boing</frog></thing></zoo>",
-		expression:     "([..] | reverse | .[]) |= [] + .",
-		expected:       "- zoo:\n    - thing:\n        - frog:\n            - boing\n",
+		description: "Parse xml: force all as an array",
+		input:       "<zoo><thing><frog>boing</frog></thing></zoo>",
+		expression:  ".. |= [] + .",
+		expected:    "- zoo:\n    - thing:\n        - frog:\n            - boing\n",
 	},
 	{
 		description:    "Parse xml: attributes",