Add more functionality to the ErLang parser (#2390)

* ERLang parser support for empty lists
* ERLang add support for single quote strings
* ERLang parser support for comments
---------
Signed-off-by: Laurent Goderre <laurent.goderre@docker.com>

syft/pkg/cataloger/erlang/erlang_parser.go

@@ -2,6 +2,7 @@ package erlang
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
 	"io"
 	"strings"
@@ -12,6 +13,8 @@ type erlangNode struct {
 	value interface{}
 }
 
+var errSkipComments = errors.New("")
+
 func (e erlangNode) Slice() []erlangNode {
 	out, ok := e.value.([]erlangNode)
 	if ok {
@@ -56,6 +59,10 @@ func parseErlang(reader io.Reader) (erlangNode, error) {
 	i := 0
 	for i < len(data) {
 		item, err := parseErlangBlock(data, &i)
+		if err == errSkipComments {
+			skipWhitespace(data, &i)
+			continue
+		}
 		if err != nil {
 			return node(nil), fmt.Errorf("%w\n%s", err, printError(data, i))
 		}
@@ -141,11 +148,26 @@ func parseErlangNode(data []byte, i *int) (erlangNode, error) {
 	c := data[*i]
 	switch c {
 	case '[', '{':
+		offset := *i + 1
+		skipWhitespace(data, &offset)
+		c2 := data[offset]
+
+		// Add support for empty lists
+		if (c == '[' && c2 == ']') || (c == '{' && c2 == '}') {
+			*i = offset + 1
+			return node(nil), nil
+		}
+
 		return parseErlangList(data, i)
 	case '"':
+		fallthrough
+	case '\'':
 		return parseErlangString(data, i)
 	case '<':
 		return parseErlangAngleString(data, i)
+	case '%':
+		parseErlangComment(data, i)
+		return node(nil), errSkipComments
 	}
 
 	if isLiteral(c) {
@@ -205,7 +227,7 @@ func parseErlangString(data []byte, i *int) (erlangNode, error) {
 		buf.WriteByte(c)
 		*i++
 	}
-	return node(buf.String()), nil
+	return node(nil), fmt.Errorf("unterminated string at %d", *i)
 }
 
 func parseErlangList(data []byte, i *int) (erlangNode, error) {
@@ -216,6 +238,10 @@ func parseErlangList(data []byte, i *int) (erlangNode, error) {
 	for *i < len(data) {
 		item, err := parseErlangNode(data, i)
 		if err != nil {
+			if err == errSkipComments {
+				skipWhitespace(data, i)
+				continue
+			}
 			return node(nil), err
 		}
 		out.value = append(out.value.([]erlangNode), item)
@@ -225,6 +251,9 @@ func parseErlangList(data []byte, i *int) (erlangNode, error) {
 		case ',':
 			*i++
 			continue
+		case '%':
+			// Starts a new comment node
+			continue
 		case ']', '}':
 			*i++
 			return out, nil
@@ -234,3 +263,19 @@ func parseErlangList(data []byte, i *int) (erlangNode, error) {
 	}
 	return out, nil
 }
+
+func parseErlangComment(data []byte, i *int) {
+	for *i < len(data) {
+		c := data[*i]
+
+		*i++
+
+		// Rest of a line is a comment. Deals with CR, LF and CR/LF
+		if c == '\n' {
+			break
+		} else if c == '\r' && data[*i] == '\n' {
+			*i++
+			break
+		}
+	}
+}