From eb1e1f495f864f24897303b5d64b3185fae869dd Mon Sep 17 00:00:00 2001
From: chiheb ben cheikh <100644963+ChihebBENCHEIKH1@users.noreply.github.com>
Date: Sat, 19 Sep 2026 13:11:13 +0100
Subject: [PATCH] json-schema : accept escaped hyphen in regex patterns
 (#29127)

---
 common/json-schema-to-grammar.cpp     |  3 ++-
 tests/test-json-schema-to-grammar.cpp | 28 ++++++++++++++++++++++++++-
 2 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/common/json-schema-to-grammar.cpp b/common/json-schema-to-grammar.cpp
index e0426098c..3349ae4fe 100644
--- a/common/json-schema-to-grammar.cpp
+++ b/common/json-schema-to-grammar.cpp
@@ -321,7 +321,8 @@ static size_t gbnf_escape_length(const std::string & pattern, size_t pos) {
         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 ']':
+        // keep in sync with parse_char() in src/llama-grammar.cpp
+        case 't': case 'r': case 'n': case '\\': case '"': case '[': case ']': case '-':
             return 2;
         default:
             return 0;
diff --git a/tests/test-json-schema-to-grammar.cpp b/tests/test-json-schema-to-grammar.cpp
index 4c4206c6e..d5873c19d 100755
--- a/tests/test-json-schema-to-grammar.cpp
+++ b/tests/test-json-schema-to-grammar.cpp
@@ -1476,6 +1476,32 @@ static void test_all(const std::string & title, std::function<void(const TestCas
         )"""
     });
 
+    test({
+        SUCCESS,
+        "regexp with escaped hyphen in a character class",
+        R"""({
+            "type": "string",
+            "pattern": "^[a-z\\-]+$"
+        })""",
+        R"""(
+            root ::= "\"" ([a-z\-]+) "\""
+            space ::= | " " | "\n"{1,2} [ \t]{0,20}
+        )"""
+    });
+
+    test({
+        SUCCESS,
+        "regexp with escaped hyphen outside a character class",
+        R"""({
+            "type": "string",
+            "pattern": "^a\\-b$"
+        })""",
+        R"""(
+            root ::= "\"" ("a\-b") "\""
+            space ::= | " " | "\n"{1,2} [ \t]{0,20}
+        )"""
+    });
+
     // a regexp that is invalid under any flavor is still an error
     test({
         FAILURE,
@@ -1494,7 +1520,7 @@ static void test_all(const std::string & title, std::function<void(const TestCas
         R"""({
             "type": "object",
             "properties": {
-                "a": { "type": "string", "pattern": "^[a-z\\-]+$" }
+                "a": { "type": "string", "pattern": "^(?=a)a$" }
             },
             "required": ["a"],
             "additionalProperties": false