Shouldn't rewrite dot in a string to index syntax (#502)

Co-authored-by: Casey Lee <cplee@nektos.com>

pkg/runner/expression.go

@@ -16,10 +16,9 @@ import (
 	"gopkg.in/godo.v2/glob"
 )
 
-var contextPattern, expressionPattern, operatorPattern *regexp.Regexp
+var expressionPattern, operatorPattern *regexp.Regexp
 
 func init() {
-	contextPattern = regexp.MustCompile(`^([^.]*(?:\[.+])*)(?:\.([\w-]+))?(.*)$`)
 	expressionPattern = regexp.MustCompile(`\${{\s*(.+?)\s*}}`)
 	operatorPattern = regexp.MustCompile("^[!=><|&]+$")
 }
@@ -123,22 +122,88 @@ func (ee *expressionEvaluator) InterpolateWithStringCheck(in string) (string, bo
 // Rewrite tries to transform any javascript property accessor into its bracket notation.
 // For instance, "object.property" would become "object['property']".
 func (ee *expressionEvaluator) Rewrite(in string) string {
-	re := in
+	var buf strings.Builder
+	r := strings.NewReader(in)
 	for {
-		matches := contextPattern.FindStringSubmatch(re)
-		if matches == nil {
-			// No global match, we're done!
+		c, _, err := r.ReadRune()
+		if err == io.EOF {
 			break
 		}
-		if matches[2] == "" {
-			// No property match, we're done!
-			break
+		//nolint
+		switch {
+		default:
+			buf.WriteRune(c)
+		case c == '\'':
+			buf.WriteRune(c)
+			ee.advString(&buf, r)
+		case c == '.':
+			buf.WriteString("['")
+			ee.advPropertyName(&buf, r)
+			buf.WriteString("']")
 		}
-
-		re = fmt.Sprintf("%s['%s']%s", matches[1], matches[2], matches[3])
 	}
+	return buf.String()
+}
 
-	return re
+func (*expressionEvaluator) advString(w *strings.Builder, r *strings.Reader) error {
+	for {
+		c, _, err := r.ReadRune()
+		if err != nil {
+			return err
+		}
+		if c != '\'' {
+			w.WriteRune(c) //nolint
+			continue
+		}
+
+		// Handles a escaped string: ex. 'It''s ok'
+		c, _, err = r.ReadRune()
+		if err != nil {
+			w.WriteString("'") //nolint
+			return err
+		}
+		if c != '\'' {
+			w.WriteString("'") //nolint
+			if err := r.UnreadRune(); err != nil {
+				return err
+			}
+			break
+		}
+		w.WriteString(`\'`) //nolint
+	}
+	return nil
+}
+
+func (*expressionEvaluator) advPropertyName(w *strings.Builder, r *strings.Reader) error {
+	for {
+		c, _, err := r.ReadRune()
+		if err != nil {
+			return err
+		}
+		if !isLetter(c) {
+			if err := r.UnreadRune(); err != nil {
+				return err
+			}
+			break
+		}
+		w.WriteRune(c) //nolint
+	}
+	return nil
+}
+
+func isLetter(c rune) bool {
+	switch {
+	case c >= 'a' && c <= 'z':
+		return true
+	case c >= 'A' && c <= 'Z':
+		return true
+	case c >= '0' && c <= '9':
+		return true
+	case c == '_' || c == '-':
+		return true
+	default:
+		return false
+	}
 }
 
 func (rc *RunContext) newVM() *otto.Otto {