Auto style when adding to empty maps/arrays

pkg/yqlib/candidate_node.go

@@ -150,7 +150,10 @@ func (n *CandidateNode) UpdateAttributesFrom(other *CandidateNode, prefs assignP
 
 	// merge will pickup the style of the new thing
 	// when autocreating nodes
-	if n.Node.Style == 0 {
+	//
+	// if this is an empty map or empty array, use the style of other node.
+
+	if n.Node.Style == 0 || (n.Node.Kind != yaml.ScalarNode && len(n.Node.Content) == 0) {
 		n.Node.Style = other.Node.Style
 	}
 

pkg/yqlib/operator_add.go

@@ -141,7 +141,9 @@ func addScalars(target *CandidateNode, lhs *yaml.Node, rhs *yaml.Node) error {
 
 func addSequences(target *CandidateNode, lhs *CandidateNode, rhs *CandidateNode) {
 	target.Node.Kind = yaml.SequenceNode
+	if len(lhs.Node.Content) > 0 {
 		target.Node.Style = lhs.Node.Style
+	}
 	target.Node.Tag = lhs.Node.Tag
 	target.Node.Content = make([]*yaml.Node, len(lhs.Node.Content))
 	copy(target.Node.Content, lhs.Node.Content)
@@ -170,6 +172,8 @@ func addMaps(target *CandidateNode, lhsC *CandidateNode, rhsC *CandidateNode) {
 		}
 	}
 	target.Node.Kind = yaml.MappingNode
+	if len(lhs.Content) > 0 {
 		target.Node.Style = lhs.Style
+	}
 	target.Node.Tag = lhs.Tag
 }

pkg/yqlib/operator_add_test.go

@@ -62,6 +62,78 @@ var addOperatorScenarios = []expressionScenario{
 			"D0, P[a], (!!seq)::[1, 2]\n",
 		},
 	},
+	{
+		skipDoc:     true,
+		description: "Concatenate to empty array",
+		document:    `{a: []}`,
+		expression:  `.a + "cat"`,
+		expected: []string{
+			"D0, P[a], (!!seq)::- cat\n",
+		},
+	},
+	{
+		skipDoc:     true,
+		description: "Concatenate to existing array",
+		document:    `{a: [dog]}`,
+		expression:  `.a + "cat"`,
+		expected: []string{
+			"D0, P[a], (!!seq)::[dog, cat]\n",
+		},
+	},
+	{
+		skipDoc:     true,
+		description: "Concatenate to empty array",
+		document:    `a: []`,
+		expression:  `.a += "cat"`,
+		expected: []string{
+			"D0, P[], (doc)::a:\n    - cat\n",
+		},
+	},
+	{
+		skipDoc:     true,
+		description: "Concatenate to existing array",
+		document:    `a: [dog]`,
+		expression:  `.a += "cat"`,
+		expected: []string{
+			"D0, P[], (doc)::a: [dog, cat]\n",
+		},
+	},
+	{
+		skipDoc:     true,
+		description: "Concatenate to empty object",
+		document:    `{a: {}}`,
+		expression:  `.a + {"b": "cat"}`,
+		expected: []string{
+			"D0, P[a], (!!map)::b: cat\n",
+		},
+	},
+	{
+		skipDoc:     true,
+		description: "Concatenate to existing object",
+		document:    `{a: {c: dog}}`,
+		expression:  `.a + {"b": "cat"}`,
+		expected: []string{
+			"D0, P[a], (!!map)::{c: dog, b: cat}\n",
+		},
+	},
+	{
+		skipDoc:     true,
+		description: "Concatenate to empty object in place",
+		document:    `a: {}`,
+		expression:  `.a += {"b": "cat"}`,
+		expected: []string{
+			"D0, P[], (doc)::a:\n    b: cat\n",
+		},
+	},
+	{
+		skipDoc:     true,
+		description: "Concatenate to existing object in place",
+		document:    `a: {c: dog}`,
+		expression:  `.a += {"b": "cat"}`,
+		expected: []string{
+			"D0, P[], (doc)::a: {c: dog, b: cat}\n",
+		},
+	},
 	{
 		description: "Add new object to array",
 		document:    `a: [{dog: woof}]`,

pkg/yqlib/operator_collect_object_test.go

@@ -19,7 +19,7 @@ var collectObjectOperatorScenarios = []expressionScenario{
 		document:   "a: []",
 		expression: `.a += [{"key": "att2", "value": "val2"}]`,
 		expected: []string{
-			"D0, P[], (doc)::a: [{key: att2, value: val2}]\n",
+			"D0, P[], (doc)::a:\n    - key: att2\n      value: val2\n",
 		},
 	},
 	{