Merge pull request #45 from JefeDavis/implement-keyName-operator

feat: add propertyName operator

README.md

@@ -19,12 +19,13 @@ Valid paths are strings conforming to the following BNF syntax.
               <recursive descent> <subpath>
 
 <child> ::= <dot child> | <bracket child>
-<dot child> ::= "." <dotted child name> | ".*"           ; named child (restricted characters) or all children
-<bracket child> ::= "[" <child names> "]"                ; named children
+<dot child> ::= "." <dotted child name> | ".*"          ; named child (restricted characters) or all children
+<bracket child> ::= "[" <child names> "]" | "[" <child names> "]~"                ; named children | property names of children
 <child names> ::= <child name> |
                   <child name> "," <child names> 
 <undotted child> ::= <dotted child name> |               ; named child (restricted characters)
                      <dotted child name><array access> | ; array access of named child
+                     <dotted child name>"~"              ; property name of child
                     "*"                                  ; all children
                     "*" <array access>                   ; array access of all children
 <child name> ::= "'" <single quoted string> "'" |
@@ -112,6 +113,9 @@ Although either form `.childname` or `['childname']` accepts a child name with e
 
 As a special case, `.*` also matches all the nodes in each sequence node in the input slice.
 
+## Property Name:
+The Property Name Operator `~` can be included after a child name in the form of `.childname~`, `['childname']~` or `['childname1', "childname2"]~` to return the property name of the node instead of the value. this can only be used on the last part of the path
+
 ### Recursive Descent: `..childname` or `..*`
 
 A matcher of the form `..childname` selects all the descendants of the nodes in the input slice (including those nodes) with the given name (using the same rules as the child matcher). The output slice consists of all the matching descendants.

pkg/yamlpath/example_test.go

@@ -64,7 +64,8 @@ spec:
 
 	err = e.Encode(&n)
 	if err != nil {
-		log.Fatalf("cannot marshal node: %v", err)
+		log.Printf("Error: cannot marshal node: %v", err)
+		return
 	}
 
 	z := `apiVersion: apps/v1

pkg/yamlpath/lexer.go

@@ -49,6 +49,9 @@ const (
 	lexemeFilterBooleanLiteral
 	lexemeFilterNullLiteral
 	lexemeFilterRegularExpressionLiteral
+	lexemePropertyName
+	lexemeBracketPropertyName
+	lexemeArraySubscriptPropertyName
 	lexemeEOF // lexing complete
 )
 
@@ -142,7 +145,6 @@ func (l lexeme) literalValue() typedValue {
 
 func sanitiseRegularExpressionLiteral(re string) string {
 	return strings.ReplaceAll(re[1:len(re)-1], `\/`, `/`)
-
 }
 
 func (l lexeme) comparator() comparator {
@@ -447,6 +449,7 @@ const (
 	filterRegularExpressionLiteralDelimiter string = "/"
 	filterRegularExpressionEscape           string = `\`
 	recursiveDescent                        string = ".."
+	propertyName                            string = "~"
 )
 
 var orderingOperators []orderingOperator
@@ -536,7 +539,7 @@ func lexSubPath(l *lexer) stateFn {
 		childName := false
 		for {
 			le := l.next()
-			if le == '.' || le == '[' || le == ')' || le == ' ' || le == '&' || le == '|' || le == '=' || le == '!' || le == '>' || le == '<' || le == eof {
+			if le == '.' || le == '[' || le == ')' || le == ' ' || le == '&' || le == '|' || le == '=' || le == '!' || le == '>' || le == '<' || le == '~' || le == eof {
 				l.backup()
 				break
 			}
@@ -545,6 +548,14 @@ func lexSubPath(l *lexer) stateFn {
 		if !childName {
 			return l.errorf("child name missing")
 		}
+		if l.consumed(propertyName) {
+			if l.peek() != eof {
+				return l.errorf("property name operator may only be used on last child in path")
+			}
+			l.emit(lexemePropertyName)
+			return lexSubPath
+		}
+
 		l.emit(lexemeDotChild)
 
 		return lexOptionalArrayIndex
@@ -572,6 +583,13 @@ func lexSubPath(l *lexer) stateFn {
 		if !l.consumedWhitespaced("]") {
 			return l.errorf(`missing "]" or ","`)
 		}
+		if l.consumed(propertyName) {
+			l.emit(lexemeBracketPropertyName)
+			if l.peek() != eof {
+				return l.errorf("property name operator may only be used on last child in path")
+			}
+			return lexSubPath
+		}
 
 		l.emit(lexemeBracketChild)
 
@@ -589,7 +607,7 @@ func lexSubPath(l *lexer) stateFn {
 		childName := false
 		for {
 			le := l.next()
-			if le == '.' || le == '[' || le == ']' || le == ')' || le == ' ' || le == '&' || le == '|' || le == '=' || le == '!' || le == '>' || le == '<' || le == eof {
+			if le == '.' || le == '[' || le == ']' || le == ')' || le == ' ' || le == '&' || le == '|' || le == '=' || le == '!' || le == '>' || le == '<' || le == '~' || le == eof {
 				l.backup()
 				break
 			}
@@ -598,6 +616,13 @@ func lexSubPath(l *lexer) stateFn {
 		if !childName {
 			return l.errorf("child name missing")
 		}
+		if l.consumed(propertyName) {
+			if l.peek() != eof {
+				return l.errorf("property name operator may only be used on last child in path")
+			}
+			l.emit(lexemePropertyName)
+			return lexSubPath
+		}
 		l.emit(lexemeUndottedChild)
 
 		return lexOptionalArrayIndex
@@ -625,6 +650,19 @@ func lexOptionalArrayIndex(l *lexer) stateFn {
 		if !validateArrayIndex(l) {
 			return nil
 		}
+		if l.consumed(propertyName) {
+			if l.peek() != eof {
+				return l.errorf("property name operator can only be used on last item in path")
+			}
+			subscript := l.value()
+			index := strings.TrimSuffix(strings.TrimPrefix(subscript, leftBracket), rightBracket+propertyName)
+			if index != "*" {
+				return l.errorf("property name operator can only be used on map nodes")
+			}
+			l.emit(lexemeArraySubscriptPropertyName)
+			return lexSubPath
+
+		}
 		l.emit(lexemeArraySubscript)
 	}