Added keys operator

pkg/yqlib/doc/Keys.md

@@ -0,0 +1,35 @@
+# Keys
+
+Use the `keys` operator to return map keys or array indices. 
+## Map keys
+Given a sample.yml file of:
+```yaml
+dog: woof
+cat: meow
+```
+then
+```bash
+yq eval 'keys' sample.yml
+```
+will output
+```yaml
+- dog
+- cat
+```
+
+## Array keys
+Given a sample.yml file of:
+```yaml
+- apple
+- banana
+```
+then
+```bash
+yq eval 'keys' sample.yml
+```
+will output
+```yaml
+- 0
+- 1
+```
+

pkg/yqlib/doc/headers/Keys.md

@@ -0,0 +1,3 @@
+# Keys
+
+Use the `keys` operator to return map keys or array indices. 

pkg/yqlib/expression_tokeniser.go

@@ -245,6 +245,7 @@ func initLexer() (*lex.Lexer, error) {
 
 	lexer.Add([]byte(`join`), opToken(joinStringOpType))
 	lexer.Add([]byte(`split`), opToken(splitStringOpType))
+	lexer.Add([]byte(`keys`), opToken(keysOpType))
 
 	lexer.Add([]byte(`style`), opAssignableToken(getStyleOpType, assignStyleOpType))
 

pkg/yqlib/lib.go

@@ -67,6 +67,8 @@ var sortKeysOpType = &operationType{Type: "SORT_KEYS", NumArgs: 1, Precedence: 5
 var joinStringOpType = &operationType{Type: "JOIN", NumArgs: 1, Precedence: 50, Handler: joinStringOperator}
 var splitStringOpType = &operationType{Type: "SPLIT", NumArgs: 1, Precedence: 50, Handler: splitStringOperator}
 
+var keysOpType = &operationType{Type: "KEYS", NumArgs: 0, Precedence: 50, Handler: keysOperator}
+
 var collectObjectOpType = &operationType{Type: "COLLECT_OBJECT", NumArgs: 0, Precedence: 50, Handler: collectObjectOperator}
 var traversePathOpType = &operationType{Type: "TRAVERSE_PATH", NumArgs: 0, Precedence: 50, Handler: traversePathOperator}
 var traverseArrayOpType = &operationType{Type: "TRAVERSE_ARRAY", NumArgs: 1, Precedence: 50, Handler: traverseArrayOperator}

pkg/yqlib/operator_keys.go

@@ -0,0 +1,54 @@
+package yqlib
+
+import (
+	"container/list"
+	"fmt"
+
+	"gopkg.in/yaml.v3"
+)
+
+func keysOperator(d *dataTreeNavigator, matchMap *list.List, expressionNode *ExpressionNode) (*list.List, error) {
+	log.Debugf("-- keysOperator")
+
+	var results = list.New()
+
+	for el := matchMap.Front(); el != nil; el = el.Next() {
+		candidate := el.Value.(*CandidateNode)
+		node := unwrapDoc(candidate.Node)
+		var targetNode *yaml.Node
+		if node.Kind == yaml.MappingNode {
+			targetNode = getMapKeys(node)
+		} else if node.Kind == yaml.SequenceNode {
+			targetNode = getIndicies(node)
+		} else {
+			return nil, fmt.Errorf("Cannot get keys of %v, keys only works for maps and arrays", node.Tag)
+		}
+
+		result := candidate.CreateChild(nil, targetNode)
+		results.PushBack(result)
+	}
+
+	return results, nil
+}
+
+func getMapKeys(node *yaml.Node) *yaml.Node {
+	contents := make([]*yaml.Node, 0)
+	for index := 0; index < len(node.Content); index = index + 2 {
+		contents = append(contents, node.Content[index])
+	}
+	return &yaml.Node{Kind: yaml.SequenceNode, Tag: "!!seq", Content: contents}
+}
+
+func getIndicies(node *yaml.Node) *yaml.Node {
+	var contents = make([]*yaml.Node, len(node.Content))
+
+	for index := range node.Content {
+		contents[index] = &yaml.Node{
+			Kind:  yaml.ScalarNode,
+			Tag:   "!!int",
+			Value: fmt.Sprintf("%v", index),
+		}
+	}
+
+	return &yaml.Node{Kind: yaml.SequenceNode, Tag: "!!seq", Content: contents}
+}

pkg/yqlib/operator_keys_test.go

@@ -0,0 +1,47 @@
+package yqlib
+
+import (
+	"testing"
+)
+
+var keysOperatorScenarios = []expressionScenario{
+	{
+		description: "Map keys",
+		document:    `{dog: woof, cat: meow}`,
+		expression:  `keys`,
+		expected: []string{
+			"D0, P[], (!!seq)::- dog\n- cat\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `{}`,
+		expression: `keys`,
+		expected: []string{
+			"D0, P[], (!!seq)::[]\n",
+		},
+	},
+	{
+		description: "Array keys",
+		document:    `[apple, banana]`,
+		expression:  `keys`,
+		expected: []string{
+			"D0, P[], (!!seq)::- 0\n- 1\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `[]`,
+		expression: `keys`,
+		expected: []string{
+			"D0, P[], (!!seq)::[]\n",
+		},
+	},
+}
+
+func TestKeysOperatorScenarios(t *testing.T) {
+	for _, tt := range keysOperatorScenarios {
+		testScenario(t, &tt)
+	}
+	documentScenarios(t, "Keys", keysOperatorScenarios)
+}