Fixes issue when update against self #1869

Author: mikefarah

pkg/yqlib/candidate_node.go

@@ -368,7 +368,10 @@ func (n *CandidateNode) doCopy(cloneContent bool) *CandidateNode {
 
 // updates this candidate from the given candidate node
 func (n *CandidateNode) UpdateFrom(other *CandidateNode, prefs assignPreferences) {
-
+	if n == other {
+		log.Debugf("UpdateFrom, no need to update from myself.")
+		return
+	}
 	// if this is an empty map or empty array, use the style of other node.
 	if (n.Kind != ScalarNode && len(n.Content) == 0) ||
 		// if the tag has changed (e.g. from str to bool)

pkg/yqlib/operator_assign_test.go

@@ -17,6 +17,15 @@ var assignOperatorScenarios = []expressionScenario{
 			"D0, P[], ()::a:\n    b: cat\nx: frog\n",
 		},
 	},
+	{
+		description: "Create yaml file",
+		document:    "a: {b: 3}",
+		expression:  `.a |= .`,
+		skipDoc:     true,
+		expected: []string{
+			"D0, P[], (!!map)::a: {b: 3}\n",
+		},
+	},
 	{
 		skipDoc:    true,
 		document:   "{}",