MDEV-11474 JSON_DEPTH returns incorrect results.

        Item_func_json_depth::val_int fixed.

mysql-test/r/func_json.result

@@ -277,3 +277,9 @@ NULL
 select json_depth(cast(NULL as JSON));
 json_depth(cast(NULL as JSON))
 NULL
+select json_depth('[[], {}]');
+json_depth('[[], {}]')
+2
+select json_depth('[[[1,2,3],"s"], {}, []]');
+json_depth('[[[1,2,3],"s"], {}, []]')
+4

mysql-test/t/func_json.test

@@ -123,4 +123,6 @@ select json_object("a", cast('{"b": "abcd"}' as json));
 
 select cast(NULL AS JSON);
 select json_depth(cast(NULL as JSON));
+select json_depth('[[], {}]');
+select json_depth('[[[1,2,3],"s"], {}, []]');
 

sql/item_jsonfunc.cc

@@ -1235,7 +1235,7 @@ longlong Item_func_json_depth::val_int()
 {
   String *js= args[0]->val_str(&tmp_js);
   json_engine_t je;
-  uint depth= 0;
+  uint depth= 0, c_depth= 0;
   bool inc_depth= TRUE;
 
   if ((null_value= args[0]->null_value))
@@ -1252,14 +1252,22 @@ longlong Item_func_json_depth::val_int()
     case JST_VALUE:
       if (inc_depth)
       {
-        depth++;
+        c_depth++;
         inc_depth= FALSE;
+        if (c_depth > depth)
+          depth= c_depth;
       }
       break;
     case JST_OBJ_START:
     case JST_ARRAY_START:
       inc_depth= TRUE;
       break;
+    case JST_OBJ_END:
+    case JST_ARRAY_END:
+      if (!inc_depth)
+        c_depth--;
+      inc_depth= FALSE;
+      break;
     default:
       break;
     }