now assumes yaml idiomatic formatting when adding to empty maps/arrays

pkg/yqlib/doc/operators/add.md

@@ -135,7 +135,9 @@ a:
     b:
       - dog
       - mouse
-  a3: {b: [mouse]}
+  a3:
+    b:
+      - mouse
 ```
 
 ## String concatenation

pkg/yqlib/doc/operators/assign-update.md

@@ -199,7 +199,8 @@ yq '.a.b |= "bogs"' sample.yml
 ```
 will output
 ```yaml
-{a: {b: bogs}}
+a:
+  b: bogs
 ```
 
 ## Update node value that has an anchor
@@ -229,6 +230,8 @@ yq '.a.b.[0] |= "bogs"' sample.yml
 ```
 will output
 ```yaml
-{a: {b: [bogs]}}
+a:
+  b:
+    - bogs
 ```
 

pkg/yqlib/operator_assign_test.go

@@ -17,7 +17,7 @@ var assignOperatorScenarios = []expressionScenario{
 		document:   "{}",
 		expression: `.a |= .b`,
 		expected: []string{
-			"D0, P[], (doc)::{a: null}\n",
+			"D0, P[], (doc)::a: null\n",
 		},
 	},
 	{
@@ -25,7 +25,7 @@ var assignOperatorScenarios = []expressionScenario{
 		document:   "{}",
 		expression: `.a = .b`,
 		expected: []string{
-			"D0, P[], (doc)::{a: null}\n",
+			"D0, P[], (doc)::a: null\n",
 		},
 	},
 	{
@@ -178,7 +178,7 @@ var assignOperatorScenarios = []expressionScenario{
 		document:              `{}`,
 		expression:            `.a.b |= "bogs"`,
 		expected: []string{
-			"D0, P[], (doc)::{a: {b: bogs}}\n",
+			"D0, P[], (doc)::a:\n    b: bogs\n",
 		},
 	},
 	{
@@ -197,7 +197,7 @@ var assignOperatorScenarios = []expressionScenario{
 		document:              `{}`,
 		expression:            `.a.b.[0] |= "bogs"`,
 		expected: []string{
-			"D0, P[], (doc)::{a: {b: [bogs]}}\n",
+			"D0, P[], (doc)::a:\n    b:\n        - bogs\n",
 		},
 	},
 	{
@@ -205,7 +205,7 @@ var assignOperatorScenarios = []expressionScenario{
 		document:   `{}`,
 		expression: `.a.b.[1].c |= "bogs"`,
 		expected: []string{
-			"D0, P[], (doc)::{a: {b: [null, {c: bogs}]}}\n",
+			"D0, P[], (doc)::a:\n    b:\n        - null\n        - c: bogs\n",
 		},
 	},
 }

pkg/yqlib/operator_collect_object_test.go

@@ -115,12 +115,12 @@ var collectObjectOperatorScenarios = []expressionScenario{
 	},
 	{
 		skipDoc:    true,
-		document:   `{name: Mike, pets: {cows: [apl, bba]}}`,
-		document2:  `{name: Rosey, pets: {sheep: [frog, meow]}}`,
+		document:   "name: Mike\npets:\n  cows:\n    - apl\n    - bba",
+		document2:  "name: Rosey\npets:\n  sheep:\n    - frog\n    - meow",
 		expression: `{"a":.name, "b":.pets}`,
 		expected: []string{
-			"D0, P[], (!!map)::a: Mike\nb: {cows: [apl, bba]}\n",
-			"D0, P[], (!!map)::a: Rosey\nb: {sheep: [frog, meow]}\n",
+			"D0, P[], (!!map)::a: Mike\nb:\n    cows:\n        - apl\n        - bba\n",
+			"D0, P[], (!!map)::a: Rosey\nb:\n    sheep:\n        - frog\n        - meow\n",
 		},
 	},
 	{

pkg/yqlib/operator_multiply_test.go

@@ -239,7 +239,7 @@ var multiplyOperatorScenarios = []expressionScenario{
 		document:   `{a: &a { b: &b { c: &c cat } } }`,
 		expression: `{} * .`,
 		expected: []string{
-			"D0, P[], (!!map)::{a: &a {b: &b {c: &c cat}}}\n",
+			"D0, P[], (!!map)::a: &a\n    b: &b\n        c: &c cat\n",
 		},
 	},
 	{
@@ -388,7 +388,7 @@ var multiplyOperatorScenarios = []expressionScenario{
 		document:   `{a: {array: [1]}, b: {}}`,
 		expression: `.b *+ .a`,
 		expected: []string{
-			"D0, P[b], (!!map)::{array: [1]}\n",
+			"D0, P[b], (!!map)::array: [1]\n",
 		},
 	},
 	{

pkg/yqlib/operator_traverse_path.go

@@ -198,6 +198,11 @@ func traverseArrayWithIndices(candidate *CandidateNode, indices []*yaml.Node, pr
 		indexToUse := index
 		contentLength := int64(len(node.Content))
 		for contentLength <= index {
+			if contentLength == 0 {
+				// default to nice yaml formating
+				node.Style = 0
+			}
+
 			node.Content = append(node.Content, &yaml.Node{Tag: "!!null", Kind: yaml.ScalarNode, Value: "null"})
 			contentLength = int64(len(node.Content))
 		}
@@ -207,7 +212,7 @@ func traverseArrayWithIndices(candidate *CandidateNode, indices []*yaml.Node, pr
 		}
 
 		if indexToUse < 0 {
-			return nil, fmt.Errorf("Index [%v] out of range, array size is %v", index, contentLength)
+			return nil, fmt.Errorf("index [%v] out of range, array size is %v", index, contentLength)
 		}
 
 		newMatches.PushBack(candidate.CreateChildInArray(int(index), node.Content[indexToUse]))
@@ -232,6 +237,11 @@ func traverseMap(context Context, matchingNode *CandidateNode, key string, prefs
 		valueNode := &yaml.Node{Tag: "!!null", Kind: yaml.ScalarNode, Value: "null"}
 		keyNode := &yaml.Node{Kind: yaml.ScalarNode, Value: key}
 		node := matchingNode.Node
+
+		if len(node.Content) == 0 {
+			node.Style = 0
+		}
+
 		node.Content = append(node.Content, keyNode, valueNode)
 
 		if prefs.IncludeMapKeys {

pkg/yqlib/operator_traverse_path_test.go

@@ -35,6 +35,22 @@ var traversePathOperatorScenarios = []expressionScenario{
 			"D0, P[0 0], (!!int)::1\n",
 		},
 	},
+	{
+		skipDoc:    true,
+		document:   `blah: {}`,
+		expression: `.blah.cat = "cool"`,
+		expected: []string{
+			"D0, P[], (doc)::blah:\n    cat: cool\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `blah: []`,
+		expression: `.blah.0 = "cool"`,
+		expected: []string{
+			"D0, P[], (doc)::blah:\n    - cool\n",
+		},
+	},
 	{
 		skipDoc:    true,
 		document:   `b: cat`,