Added is_key operator

pkg/yqlib/doc/operators/keys.md

@@ -118,3 +118,43 @@ will output
 comment on key
 ```
 
+## Check node is a key
+Given a sample.yml file of:
+```yaml
+a:
+  b:
+    - cat
+  c: frog
+```
+then
+```bash
+yq '[... | { "p": path | join("."), "isKey": is_key, "tag": tag }]' sample.yml
+```
+will output
+```yaml
+- p: ""
+  isKey: false
+  tag: '!!map'
+- p: a
+  isKey: true
+  tag: '!!str'
+- p: a
+  isKey: false
+  tag: '!!map'
+- p: a.b
+  isKey: true
+  tag: '!!str'
+- p: a.b
+  isKey: false
+  tag: '!!seq'
+- p: a.b.0
+  isKey: false
+  tag: '!!str'
+- p: a.c
+  isKey: true
+  tag: '!!str'
+- p: a.c
+  isKey: false
+  tag: '!!str'
+```
+

pkg/yqlib/lexer_participle.go

@@ -123,6 +123,7 @@ var participleYqRules = []*participleYqRule{
 
 	simpleOp("keys", keysOpType),
 	simpleOp("key", getKeyOpType),
+	simpleOp("is_?key", isKeyOpType),
 
 	simpleOp("file_?name|fileName", getFilenameOpType),
 	simpleOp("file_?index|fileIndex|fi", getFileIndexOpType),

pkg/yqlib/lib.go

@@ -121,6 +121,7 @@ var getStyleOpType = &operationType{Type: "GET_STYLE", NumArgs: 0, Precedence: 5
 var getTagOpType = &operationType{Type: "GET_TAG", NumArgs: 0, Precedence: 50, Handler: getTagOperator}
 
 var getKeyOpType = &operationType{Type: "GET_KEY", NumArgs: 0, Precedence: 50, Handler: getKeyOperator}
+var isKeyOpType = &operationType{Type: "IS_KEY", NumArgs: 0, Precedence: 50, Handler: isKeyOperator}
 var getParentOpType = &operationType{Type: "GET_PARENT", NumArgs: 0, Precedence: 50, Handler: getParentOperator}
 
 var getCommentOpType = &operationType{Type: "GET_COMMENT", NumArgs: 0, Precedence: 50, Handler: getCommentsOperator}

pkg/yqlib/operator_keys.go

@@ -7,6 +7,20 @@ import (
 	"gopkg.in/yaml.v3"
 )
 
+func isKeyOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	log.Debugf("-- isKeyOperator")
+
+	var results = list.New()
+
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
+		candidate := el.Value.(*CandidateNode)
+
+		results.PushBack(createBooleanCandidate(candidate, candidate.IsMapKey))
+	}
+
+	return context.ChildContext(results), nil
+}
+
 func getKeyOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("-- getKeyOperator")
 

pkg/yqlib/operator_keys_test.go

@@ -4,6 +4,32 @@ import (
 	"testing"
 )
 
+var expectedIsKey = `D0, P[], (!!seq)::- p: ""
+  isKey: false
+  tag: '!!map'
+- p: a
+  isKey: true
+  tag: '!!str'
+- p: a
+  isKey: false
+  tag: '!!map'
+- p: a.b
+  isKey: true
+  tag: '!!str'
+- p: a.b
+  isKey: false
+  tag: '!!seq'
+- p: a.b.0
+  isKey: false
+  tag: '!!str'
+- p: a.c
+  isKey: true
+  tag: '!!str'
+- p: a.c
+  isKey: false
+  tag: '!!str'
+`
+
 var keysOperatorScenarios = []expressionScenario{
 	{
 		description: "Map keys",
@@ -75,6 +101,14 @@ var keysOperatorScenarios = []expressionScenario{
 			"D0, P[a x], (!!str)::comment on key\n",
 		},
 	},
+	{
+		description: "Check node is a key",
+		document:    "a: \n  b: [cat]\n  c: frog\n",
+		expression:  `[... | { "p": path | join("."), "isKey": is_key, "tag": tag }]`,
+		expected: []string{
+			expectedIsKey,
+		},
+	},
 }
 
 func TestKeysOperatorScenarios(t *testing.T) {