MDEV-38264: Fix failed assertion in json_find_path with trailing commas

The function json_skip_array_and_count() was trapping syntax errors
(e.g., trailing commas) in a local engine copy. Because the error state
wasn't propagated back to the main engine, json_find_path() would
proceed with an inconsistent state, eventually triggering an assertion
failure.

This patch ensures that any error encountered during the lookahead
scan is propagated to the primary engine. This allows the parser to
fail gracefully with a syntax error instead of crashing.

Author: abhishek593

mysql-test/main/func_json.result

@@ -2771,3 +2771,27 @@ SELECT JSON_VALUE('{"a":[1,2]}', '$.a[*]');
 JSON_VALUE('{"a":[1,2]}', '$.a[*]')
 NULL
 # End of 10.11 Test
+#
+# MDEV-38264 Assertion in json_find_path() fails after computing
+# array size of invalid json structure
+#
+SELECT JSON_QUERY('{ "A": [0,] }', '$.A[-1]');
+JSON_QUERY('{ "A": [0,] }', '$.A[-1]')
+NULL
+SELECT JSON_VALUE('{ "A": [0,] }', '$.A[-1]');
+JSON_VALUE('{ "A": [0,] }', '$.A[-1]')
+NULL
+SELECT JSON_VALUE('{ "A": [5,] }', '$.A[-2]');
+JSON_VALUE('{ "A": [5,] }', '$.A[-2]')
+NULL
+SELECT JSON_VALUE('{ "A": [5] }', '$.A[-2]');
+JSON_VALUE('{ "A": [5] }', '$.A[-2]')
+NULL
+SELECT JSON_LENGTH('{ "A": [0,] }', '$.A');
+JSON_LENGTH('{ "A": [0,] }', '$.A')
+NULL
+Warnings:
+Warning	4038	Syntax error in JSON text in argument 1 to function 'json_length' at position 11
+SELECT JSON_VALID('{ "A": [0,] }');
+JSON_VALID('{ "A": [0,] }')
+0

mysql-test/main/func_json.test

@@ -2033,3 +2033,16 @@ COLUMNS(NAME VARCHAR(30) PATH '$.NAME')) AS t_sz;
 SELECT JSON_VALUE('{"a":[1,2]}', '$.a[*]');
 
 --echo # End of 10.11 Test
+
+--echo #
+--echo # MDEV-38264 Assertion in json_find_path() fails after computing
+--echo # array size of invalid json structure
+--echo #
+
+SELECT JSON_QUERY('{ "A": [0,] }', '$.A[-1]');
+SELECT JSON_VALUE('{ "A": [0,] }', '$.A[-1]');
+SELECT JSON_VALUE('{ "A": [5,] }', '$.A[-2]');
+SELECT JSON_VALUE('{ "A": [5] }', '$.A[-2]');
+SELECT JSON_LENGTH('{ "A": [0,] }', '$.A');
+SELECT JSON_VALID('{ "A": [0,] }');
+

strings/json_lib.c

@@ -1306,9 +1306,13 @@ int json_skip_level_and_count(json_engine_t *j, int *n_items_skipped)
 int json_skip_array_and_count(json_engine_t *je, int *n_items)
 {
   json_engine_t j= *je;
+  int res;
   *n_items= 0;
 
-  return json_skip_level_and_count(&j, n_items); 
+  res= json_skip_level_and_count(&j, n_items);
+  if (res)
+    je->s.error= j.s.error;
+  return res;
 }