MDEV-22976 CAST(JSON_EXTRACT() AS DECIMAL) does not handle boolean values

Item_func_json_extract did not implement val_decimal(),
so CAST(JSON_EXTRACT('{"x":true}', '$.x') AS DECIMAL) erroneously
returned 0 with a warning because of convertion from the string "true"
to decimal.

Implementing val_decimal(), so boolean values are correctly handled.

mysql-test/r/func_json.result

@@ -916,5 +916,18 @@ NULL
 Warnings:
 Warning	4037	Unexpected end of JSON text in argument 2 to function 'json_merge_patch'
 #
+# MDEV-22976 CAST(JSON_EXTRACT() AS DECIMAL) does not handle boolean values
+#
+SELECT
+CAST(JSON_EXTRACT('{"x":true}', '$.x') AS DOUBLE) AS cf,
+CAST(JSON_EXTRACT('{"x":true}', '$.x') AS DECIMAL) AS cd;
+cf	cd
+1	1
+SELECT
+CAST(JSON_EXTRACT('{"x":false}', '$.x') AS DOUBLE) AS cf,
+CAST(JSON_EXTRACT('{"x":false}', '$.x') AS DECIMAL) AS cd;
+cf	cd
+0	0
+#
 # End of 10.2 tests
 #

mysql-test/t/func_json.test

@@ -540,6 +540,19 @@ SELECT JSON_MERGE_PATCH('{}');
 SELECT JSON_MERGE_PATCH('{', '[1,2,3]');
 SELECT JSON_MERGE_PATCH('{"a":"b"}', '[1,');
 
+--echo #
+--echo # MDEV-22976 CAST(JSON_EXTRACT() AS DECIMAL) does not handle boolean values
+--echo #
+
+SELECT
+  CAST(JSON_EXTRACT('{"x":true}', '$.x') AS DOUBLE) AS cf,
+  CAST(JSON_EXTRACT('{"x":true}', '$.x') AS DECIMAL) AS cd;
+
+SELECT
+  CAST(JSON_EXTRACT('{"x":false}', '$.x') AS DOUBLE) AS cf,
+  CAST(JSON_EXTRACT('{"x":false}', '$.x') AS DECIMAL) AS cd;
+
+
 --echo #
 --echo # End of 10.2 tests
 --echo #

sql/item_jsonfunc.cc

@@ -962,6 +962,41 @@ double Item_func_json_extract::val_real()
 }
 
 
+my_decimal *Item_func_json_extract::val_decimal(my_decimal *to)
+{
+  json_value_types type;
+  char *value;
+  int value_len;
+
+  if (read_json(NULL, &type, &value, &value_len) != NULL)
+  {
+    switch (type)
+    {
+      case JSON_VALUE_STRING:
+      case JSON_VALUE_NUMBER:
+      {
+        my_decimal *res= decimal_from_string_with_check(to, collation.collation,
+                                                        value,
+                                                        value + value_len);
+        null_value= res == NULL;
+        return res;
+      }
+      case JSON_VALUE_TRUE:
+        int2my_decimal(E_DEC_FATAL_ERROR, 1, false/*unsigned_flag*/, to);
+        return to;
+      case JSON_VALUE_OBJECT:
+      case JSON_VALUE_ARRAY:
+      case JSON_VALUE_FALSE:
+      case JSON_VALUE_NULL:
+        break;
+    };
+  }
+  int2my_decimal(E_DEC_FATAL_ERROR, 0, false/*unsigned_flag*/, to);
+  return to;
+}
+
+
+
 bool Item_func_json_contains::fix_length_and_dec()
 {
   a2_constant= args[1]->const_item();

sql/item_jsonfunc.h

@@ -171,6 +171,7 @@ public:
   String *val_str(String *);
   longlong val_int();
   double val_real();
+  my_decimal *val_decimal(my_decimal *);
   uint get_n_paths() const { return arg_count - 1; }
   Item *get_copy(THD *thd, MEM_ROOT *mem_root)
   { return get_item_copy<Item_func_json_extract>(thd, mem_root, this); }