Improve error messages for eof

Author: antonmedv

expr_test.go

@@ -108,9 +108,9 @@ func ExampleEval_matches() {
 
 	fmt.Printf("%v", output)
 
-	// Output: error parsing regexp: missing closing ): `a(` (1:17)
+	// Output: error parsing regexp: missing closing ): `a(` (1:16)
 	//  | "a" matches "a("
-	//  | ................^
+	//  | ...............^
 }
 
 func ExampleCompile() {

parser/lexer/lexer.go

@@ -69,6 +69,14 @@ func (l *lexer) emitValue(t Kind, value string) {
 	l.start = l.end
 }
 
+func (l *lexer) emitEOF() {
+	l.tokens = append(l.tokens, Token{
+		Location: l.loc(l.start - 1), // Point to previous position for better error messages.
+		Kind:     EOF,
+	})
+	l.start = l.end
+}
+
 func (l *lexer) word() string {
 	return l.input[l.start:l.end]
 }

parser/lexer/state.go

@@ -9,7 +9,7 @@ type stateFn func(*lexer) stateFn
 func root(l *lexer) stateFn {
 	switch r := l.next(); {
 	case r == eof:
-		l.emit(EOF)
+		l.emitEOF()
 		return nil
 	case isSpace(r):
 		l.ignore()

parser/parser.go

@@ -145,7 +145,7 @@ func (p *parser) parseExpression(precedence int) Node {
 	nodeLeft := p.parsePrimary()
 
 	token := p.current
-	for token.Is(Operator) {
+	for token.Is(Operator) && p.err == nil {
 		if op, ok := binaryOperators[token.Value]; ok {
 			if op.precedence >= precedence {
 				p.next()
@@ -230,7 +230,7 @@ func (p *parser) parsePrimary() Node {
 
 func (p *parser) parseConditionalExpression(node Node) Node {
 	var expr1, expr2 Node
-	for p.current.Is(Operator, "?") {
+	for p.current.Is(Operator, "?") && p.err == nil {
 		p.next()
 
 		if !p.current.Is(Operator, ":") {
@@ -371,7 +371,7 @@ func (p *parser) parseMapExpression(token Token) Node {
 	p.expect(Bracket, "{")
 
 	nodes := make([]Node, 0)
-	for !p.current.Is(Bracket, "}") {
+	for !p.current.Is(Bracket, "}") && p.err == nil {
 		if len(nodes) > 0 {
 			p.expect(Operator, ",")
 		}
@@ -404,27 +404,15 @@ func (p *parser) parseMapExpression(token Token) Node {
 
 func (p *parser) parsePostfixExpression(node Node) Node {
 	token := p.current
-	for token.Is(Operator) || token.Is(Bracket) {
+	for (token.Is(Operator) || token.Is(Bracket)) && p.err == nil {
 		if token.Value == "." {
 			p.next()
 
 			token = p.current
 			p.next()
 
 			if token.Kind != Identifier &&
-				// Operators like "not" and "matches" are valid method or property names,
-				//
-				// In other words, besides name token kind, operator kind could also be parsed as a property or method.
-				// This is because operators are processed by the lexer prior to names. So "not" in "foo.not()"
-				// or "matches" in "foo.matches" will be recognized as an operator first. But in fact, "not"
-				// and "matches" in such expressions shall be parsed as method or property names.
-				//
-				// And this ONLY works if the operator consists of valid characters for a property or method name.
-				//
-				// Other types, such as text kind and number kind, can't be parsed as property nor method names.
-				//
-				// As a result, if token is NOT an operator OR token.value is NOT a valid property or method name,
-				// an error shall be returned.
+				// Operators like "not" and "matches" are valid methods or property names.
 				(token.Kind != Operator || !isValidIdentifier(token.Value)) {
 				p.error("expected name")
 			}
@@ -535,7 +523,7 @@ func (p *parser) parseList(start, end string) []Node {
 	p.expect(Bracket, start)
 
 	nodes := make([]Node, 0)
-	for !p.current.Is(Bracket, end) {
+	for !p.current.Is(Bracket, end) && p.err == nil {
 		if len(nodes) > 0 {
 			p.expect(Operator, ",")
 		}

parser/parser_test.go

@@ -227,14 +227,14 @@ func TestParse(t *testing.T) {
 
 const errorTests = `
 foo.
-unexpected end of expression (1:5)
+unexpected end of expression (1:4)
  | foo.
- | ....^
+ | ...^
 
 a+
-unexpected token EOF (1:3)
+unexpected token EOF (1:2)
  | a+
- | ..^
+ | .^
 
 a ? (1+2) c
 unexpected token Identifier("c") (1:11)
@@ -257,9 +257,9 @@ a map key must be a quoted string, a number, a identifier, or an expression encl
  | .^
 
 a matches 'a:)b'
-error parsing regexp: unexpected ): ` + "`a:)b`" + ` (1:17)
+error parsing regexp: unexpected ): ` + "`a:)b`" + ` (1:16)
  | a matches 'a:)b'
- | ................^
+ | ...............^
 
 foo({.bar})
 a map key must be a quoted string, a number, a identifier, or an expression enclosed in parentheses (unexpected token Operator(".")) (1:6)