common : gracefully fallback on unsupported regex patterns in JSON schema (#26939)

common/json-schema-to-grammar.cpp

@@ -278,7 +278,9 @@ static std::unordered_map<char, std::string> GRAMMAR_LITERAL_ESCAPES = {
     {'\r', "\\r"}, {'\n', "\\n"}, {'"', "\\\""}, {'-', "\\-"}, {']', "\\]"}, {'\\', "\\\\"}
 };
 
-static std::unordered_set<char> NON_LITERAL_SET = {'|', '.', '(', ')', '[', ']', '{', '}', '*', '+', '?'};
+static const int MAX_PATTERN_DEPTH = 100;
+
+static std::unordered_set<char> NON_LITERAL_SET = {'|', '.', '(', ')', '[', ']', '{', '}', '*', '+', '?', '^', '$'};
 static std::unordered_set<char> ESCAPED_IN_REGEXPS_BUT_NOT_IN_LITERALS = {'^', '$', '.', '[', ']', '(', ')', '|', '{', '}', '*', '+', '?'};
 
 static std::string replacePattern(const std::string & input, const std::regex & regex, const std::function<std::string(const std::smatch  &)> & replacement) {
@@ -309,6 +311,32 @@ static std::string format_literal(const std::string & literal) {
 
 std::string gbnf_format_literal(const std::string & literal) { return format_literal(literal); }
 
+static size_t gbnf_escape_length(const std::string & pattern, size_t pos) {
+    if (pos + 1 >= pattern.length() || pattern[pos] != '\\') {
+        return 0;
+    }
+    size_t n_hex = 0;
+    switch (pattern[pos + 1]) {
+        case 'x': n_hex = 2; break;
+        case 'u': n_hex = 4; break;
+        case 'U': n_hex = 8; break;
+        case 't': case 'r': case 'n': case '\\': case '"': case '[': case ']':
+            return 2;
+        default:
+            return 0;
+    }
+    if (pos + 2 + n_hex > pattern.length()) {
+        return 0;
+    }
+    for (size_t i = pos + 2; i < pos + 2 + n_hex; i++) {
+        char h = pattern[i];
+        if (!((h >= '0' && h <= '9') || (h >= 'a' && h <= 'f') || (h >= 'A' && h <= 'F'))) {
+            return 0;
+        }
+    }
+    return 2 + n_hex;
+}
+
 class common_schema_converter {
 private:
     friend class common_schema_info;
@@ -345,16 +373,42 @@ private:
         return string_join(rules, " | ");
     }
 
+    // thrown when the pattern is a valid regex with no grammar equivalent
+    struct unsupported_pattern : public std::runtime_error {
+        using std::runtime_error::runtime_error;
+    };
+
+    // thrown when the pattern is not a valid regex
+    struct invalid_pattern : public std::runtime_error {
+        using std::runtime_error::runtime_error;
+    };
+
     std::string _visit_pattern(const std::string & pattern, const std::string & name) {
-        if (!(pattern.front() == '^' && pattern.back() == '$')) {
+        auto rules_snapshot = _rules;
-            _errors.push_back("Pattern must start with '^' and end with '$'");
+        try {
+            return _pattern_to_rule(pattern, name);
+        } catch (const unsupported_pattern & err) {
+            // revert rules
+            _rules = std::move(rules_snapshot);
+            _warnings.push_back("pattern " + pattern + " is not supported (" + err.what() + "), accepting any string");
+            return _add_rule(name, _add_primitive("string", PRIMITIVE_RULES.at("string")));
+        } catch (const invalid_pattern & err) {
+            _rules = std::move(rules_snapshot);
+            _errors.push_back("Invalid pattern " + pattern + ": " + err.what());
             return "";
         }
+    }
+
+    std::string _pattern_to_rule(const std::string & pattern, const std::string & name) {
+        if (pattern.length() < 2 || pattern.front() != '^' || pattern.back() != '$') {
+            throw unsupported_pattern("not anchored with '^' and '$'");
+        }
         std::string sub_pattern = pattern.substr(1, pattern.length() - 2);
         std::unordered_map<std::string, std::string> sub_rule_ids;
 
         size_t i = 0;
         size_t length = sub_pattern.length();
+        int paren_depth = 0;
 
         using literal_or_rule = std::pair<std::string, bool>;
         auto to_rule = [&](const literal_or_rule & ls) {
@@ -363,7 +417,6 @@ private:
             return is_literal ? "\"" + s + "\"" : s;
         };
         std::function<literal_or_rule()> transform = [&]() -> literal_or_rule {
-            size_t start = i;
             std::vector<literal_or_rule> seq;
 
             auto get_dot = [&]() {
@@ -420,43 +473,42 @@ private:
                         if (i + 1 < length && sub_pattern[i + 1] == ':') {
                             i += 2; // skip "?:" for non-capturing group, treat as regular group
                         } else {
-                            // lookahead/lookbehind (?=, ?!, ?<=, ?<!) - not supported
+                            // lookaround, named group, inline flags, ...
-                            _warnings.push_back("Unsupported pattern syntax");
+                            throw unsupported_pattern("unsupported group syntax");
-                            // skip to matching ')' to avoid UB on empty seq
-                            int depth = 1;
-                            while (i < length && depth > 0) {
-                                if (sub_pattern[i] == '\\' && i + 1 < length) {
-                                    i += 2; // skip escaped character
-                                } else {
-                                    if (sub_pattern[i] == '(') depth++;
-                                    else if (sub_pattern[i] == ')') depth--;
-                                    i++;
                         }
                     }
-                            continue;
+                    paren_depth++;
-                        }
+                    if (paren_depth > MAX_PATTERN_DEPTH) {
+                        throw unsupported_pattern("pattern nesting too deep");
                     }
                     seq.emplace_back("(" + to_rule(transform()) + ")", false);
                 } else if (c == ')') {
                     i++;
-                    if (start > 0 && sub_pattern[start - 1] != '(' && (start < 2 || sub_pattern[start - 2] != '?' || sub_pattern[start - 1] != ':')) {
+                    if (paren_depth == 0) {
-                        _errors.push_back("Unbalanced parentheses");
+                        throw invalid_pattern("unbalanced parentheses");
                     }
+                    paren_depth--;
                     return join_seq();
+                } else if (c == '^' || c == '$') {
+                    throw unsupported_pattern("anchor inside the pattern");
                 } else if (c == '[') {
                     std::string square_brackets = std::string(1, c);
                     i++;
                     while (i < length && sub_pattern[i] != ']') {
                         if (sub_pattern[i] == '\\') {
-                            square_brackets += sub_pattern.substr(i, 2);
+                            auto escape_length = gbnf_escape_length(sub_pattern, i);
-                            i += 2;
+                            if (escape_length == 0) {
+                                throw unsupported_pattern("unsupported escape in character class: " + sub_pattern.substr(i, 2));
+                            }
+                            square_brackets += sub_pattern.substr(i, escape_length);
+                            i += escape_length;
                         } else {
                             square_brackets += sub_pattern[i];
                             i++;
                         }
                     }
                     if (i >= length) {
-                        _errors.push_back("Unbalanced square brackets");
+                        throw invalid_pattern("unterminated character class");
                     }
                     square_brackets += ']';
                     i++;
@@ -465,6 +517,9 @@ private:
                     seq.emplace_back("|", false);
                     i++;
                 } else if (c == '*' || c == '+' || c == '?') {
+                    if (seq.empty()) {
+                        throw invalid_pattern("nothing to repeat");
+                    }
                     seq.back() = std::make_pair(to_rule(seq.back()) + c, false);
                     i++;
                 } else if (c == '{') {
@@ -475,18 +530,19 @@ private:
                         i++;
                     }
                     if (i >= length) {
-                        _errors.push_back("Unbalanced curly brackets");
+                        throw unsupported_pattern("unterminated curly brackets");
                     }
                     curly_brackets += '}';
                     i++;
                     auto nums = string_split(curly_brackets.substr(1, curly_brackets.length() - 2), ",");
                     int min_times = 0;
                     int max_times = std::numeric_limits<int>::max();
+                    if (nums.size() != 1 && nums.size() != 2) {
+                        throw unsupported_pattern("wrong number of values in curly brackets");
+                    }
                     try {
                         if (nums.size() == 1) {
                             min_times = max_times = std::stoi(nums[0]);
-                        } else if (nums.size() != 2) {
-                            _errors.push_back("Wrong number of values in curly brackets");
                         } else {
                             if (!nums[0].empty()) {
                                 min_times = std::stoi(nums[0]);
@@ -495,9 +551,11 @@ private:
                                 max_times = std::stoi(nums[1]);
                             }
                         }
-                    } catch (const std::invalid_argument & e) {
+                    } catch (const std::logic_error &) {
-                        _errors.push_back("Invalid number in curly brackets");
+                        throw unsupported_pattern("invalid number in curly brackets");
-                        return std::make_pair("", false);
+                    }
+                    if (seq.empty()) {
+                        throw invalid_pattern("nothing to repeat");
                     }
                     auto &last = seq.back();
                     auto &sub = last.first;
@@ -523,15 +581,22 @@ private:
                         return NON_LITERAL_SET.find(c) != NON_LITERAL_SET.end();
                     };
                     while (i < length) {
-                        if (sub_pattern[i] == '\\' && i < length - 1) {
+                        if (sub_pattern[i] == '\\') {
+                            if (i == length - 1) {
+                                throw invalid_pattern("trailing backslash");
+                            }
                             char next = sub_pattern[i + 1];
                             if (ESCAPED_IN_REGEXPS_BUT_NOT_IN_LITERALS.find(next) != ESCAPED_IN_REGEXPS_BUT_NOT_IN_LITERALS.end()) {
                                 i++;
                                 literal += sub_pattern[i];
                                 i++;
                             } else {
-                                literal += sub_pattern.substr(i, 2);
+                                auto escape_length = gbnf_escape_length(sub_pattern, i);
-                                i += 2;
+                                if (escape_length == 0) {
+                                    throw unsupported_pattern("unsupported escape: " + sub_pattern.substr(i, 2));
+                                }
+                                literal += sub_pattern.substr(i, escape_length);
+                                i += escape_length;
                             }
                         } else if (sub_pattern[i] == '"') {
                             literal += "\\\"";
@@ -544,14 +609,21 @@ private:
                             break;
                         }
                     }
-                    if (!literal.empty()) {
+                    if (literal.empty()) { // nothing was consumed, ex. a stray ']' or '}'
-                        seq.emplace_back(literal, true);
+                        throw unsupported_pattern(std::string("unsupported character: ") + c);
                     }
+                    seq.emplace_back(literal, true);
                 }
             }
             return join_seq();
         };
-        return _add_rule(name, "\"\\\"\" (" + to_rule(transform()) + ") \"\\\"\"");
+
+        auto rule = to_rule(transform());
+        if (paren_depth != 0) {
+            throw invalid_pattern("unbalanced parentheses");
+        }
+
+        return _add_rule(name, "\"\\\"\" (" + rule + ") \"\\\"\"");
     }
 
     /*

tests/test-json-schema-to-grammar.cpp

@@ -1564,6 +1564,70 @@ int main() {
                 space ::= | " " | "\n"{1,2} [ \t]{0,20}
             )""",
         });
+
+        run({
+            SUCCESS,
+            "unanchored regexp",
+            R"""({
+                "type": "string",
+                "pattern": "[0-9]+"
+            })""",
+            R"""(
+                char ::= [^"\\\x7F\x00-\x1F] | [\\] (["\\bfnrt] | "u" [0-9a-fA-F]{4})
+                root ::= string
+                space ::= | " " | "\n"{1,2} [ \t]{0,20}
+                string ::= "\"" char* "\""
+            )""",
+        });
+
+        // the rules of the partial conversion (here "root-0") must not leak into the grammar
+        run({
+            SUCCESS,
+            "regexp with unsupported shorthand",
+            R"""({
+                "type": "string",
+                "pattern": "^[0-9]{3}\\w$"
+            })""",
+            R"""(
+                char ::= [^"\\\x7F\x00-\x1F] | [\\] (["\\bfnrt] | "u" [0-9a-fA-F]{4})
+                root ::= string
+                space ::= | " " | "\n"{1,2} [ \t]{0,20}
+                string ::= "\"" char* "\""
+            )""",
+        });
+
+        // a regexp that is invalid under any flavor is still an error
+        run({
+            FAILURE,
+            "regexp with unbalanced parentheses",
+            R"""({
+                "type": "string",
+                "pattern": "^(a$"
+            })""",
+            ""
+        });
+
+        // only the property with the bad pattern degrades
+        run({
+            SUCCESS,
+            "unsupported regexp in a property",
+            R"""({
+                "type": "object",
+                "properties": {
+                    "a": { "type": "string", "pattern": "^[a-z\\-]+$" }
+                },
+                "required": ["a"],
+                "additionalProperties": false
+            })""",
+            R"""(
+                a ::= string
+                a-kv ::= "\"a\"" space ":" space a
+                char ::= [^"\\\x7F\x00-\x1F] | [\\] (["\\bfnrt] | "u" [0-9a-fA-F]{4})
+                root ::= "{" space a-kv space "}"
+                space ::= | " " | "\n"{1,2} [ \t]{0,20}
+                string ::= "\"" char* "\""
+            )""",
+        });
     }
 
     if (getenv("LLAMA_SKIP_TESTS_SLOW_ON_EMULATOR")) {