tokenize: disallow zero-length matches

Author: cebtenzzre

include/minja/minja.hpp

@@ -2336,6 +2336,11 @@ class Parser {
               throw std::runtime_error("Unexpected block: " + keyword);
             }
           } else if (std::regex_search(it, end, match, non_text_open_regex)) {
+            if (!match.position()) {
+                if (match[0] != "{#")
+                    throw std::runtime_error("Internal error: Expected a comment");
+                throw std::runtime_error("Missing end of comment tag");
+            }
             auto text_end = it + match.position();
             text = std::string(it, text_end);
             it = text_end;

tests/test-syntax.cpp

@@ -522,6 +522,7 @@ TEST(SyntaxTest, SimpleCases) {
         EXPECT_THAT([]() { render("{% if 1 %}{% else %}", {}, {}); }, ThrowsWithSubstr("Unterminated if"));
         EXPECT_THAT([]() { render("{% if 1 %}{% else %}{% elif 1 %}{% endif %}", {}, {}); }, ThrowsWithSubstr("Unterminated if"));
         EXPECT_THAT([]() { render("{% filter trim %}", {}, {}); }, ThrowsWithSubstr("Unterminated filter"));
+        EXPECT_THAT([]() { render("{# ", {}, {}); }, ThrowsWithSubstr("Missing end of comment tag"));
     }
 
     EXPECT_EQ(