Stop lexing when hitting EOF

lex.go

@@ -290,6 +290,8 @@ func stateIdent(l *lexer) stateFn {
 Loop:
 	for {
 		switch r := l.peek(); {
+		case r == eof:
+			return l.errorf("unclosed tag")
 		case !whitespace(r) && !strings.HasPrefix(l.input[l.pos:], l.rightDelim):
 			// absorb
 			l.next()

parse_test.go

@@ -4,6 +4,7 @@ package mustache
 
 import (
 	"reflect"
+	"strings"
 	"testing"
 )
 
@@ -99,3 +100,21 @@ func TestParser(t *testing.T) {
 		}
 	}
 }
+
+func TestParserNegative(t *testing.T) {
+	for _, test := range []struct {
+		template string
+		expErr   string
+	}{
+		{
+			"{{foo}",
+			`1:6 syntax error: unreachable code t_error:"unclosed tag"`,
+		},
+	} {
+		parser := newParser(newLexer(test.template, "{{", "}}"))
+		_, err := parser.parse()
+		if err == nil || !strings.Contains(err.Error(), test.expErr) {
+			t.Errorf("expect error: %q, got %q", test.expErr, err)
+		}
+	}
+}