MDEV-7001 Bad result for NOT NOT STRCMP('a','b') and NOT NOT NULLIF(2,3)

The bug is not very important per se, but it was helpful to move
Item_func_strcmp out of Item_bool_func2 (to Item_int_func),
for the purposes of "MDEV-4912 Add a plugin to field types (column types)".

mysql-test/r/func_test.result

@@ -320,3 +320,20 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 Warnings:
 Note	1003	select `test`.`t1`.`a` AS `a` from `test`.`t1` where (not((`test`.`t1`.`a` + 0)))
 drop table t1;
+#
+# Start of 10.0 tests
+#
+#
+# MDEV-7001 Bad result for NOT NOT STRCMP('a','b') and NOT NOT NULLIF(2,3)
+#
+SELECT NOT NOT strcmp('a','b');
+NOT NOT strcmp('a','b')
+1
+EXPLAIN EXTENDED SELECT NOT NOT strcmp('a','b');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+Warnings:
+Note	1003	select (strcmp('a','b') <> 0) AS `NOT NOT strcmp('a','b')`
+#
+# End of 10.0 tests
+#

mysql-test/r/null.result

@@ -382,3 +382,15 @@ CREATE TABLE t2 (d DATE) ENGINE=MyISAM;
 SELECT  * FROM t1,t2 WHERE  1 IS NOT NULL AND t1.b IS NULL;
 a	b	c	d
 DROP TABLE t1,t2;
+#
+# Start of 10.0 tests
+#
+#
+# MDEV-7001 Bad result for NOT NOT STRCMP('a','b') and NOT NOT NULLIF(2,3) 
+#
+SELECT NOT NOT NULLIF(2,3);
+NOT NOT NULLIF(2,3)
+1
+#
+# End of 10.0 tests
+#

mysql-test/t/func_test.test

@@ -180,3 +180,17 @@ select * from t1 where not (a+0);
 explain extended select * from t1 where not (a+0);
 
 drop table t1;
+
+--echo #
+--echo # Start of 10.0 tests
+--echo #
+
+--echo #
+--echo # MDEV-7001 Bad result for NOT NOT STRCMP('a','b') and NOT NOT NULLIF(2,3)
+--echo #
+SELECT NOT NOT strcmp('a','b');
+EXPLAIN EXTENDED SELECT NOT NOT strcmp('a','b');
+
+--echo #
+--echo # End of 10.0 tests
+--echo #

mysql-test/t/null.test

@@ -295,3 +295,16 @@ CREATE TABLE t2 (d DATE) ENGINE=MyISAM;
 SELECT  * FROM t1,t2 WHERE  1 IS NOT NULL AND t1.b IS NULL;
 
 DROP TABLE t1,t2;
+
+--echo #
+--echo # Start of 10.0 tests
+--echo #
+
+--echo #
+--echo # MDEV-7001 Bad result for NOT NOT STRCMP('a','b') and NOT NOT NULLIF(2,3) 
+--echo #
+SELECT NOT NOT NULLIF(2,3);
+
+--echo #
+--echo # End of 10.0 tests
+--echo #

sql/item.h

@@ -164,6 +164,12 @@ public:
       default: return "UNKNOWN";
     }
   }
+  int sortcmp(const String *s, const String *t) const
+  {
+    return collation->coll->strnncollsp(collation,
+                                        (uchar *) s->ptr(), s->length(),
+                                        (uchar *) t->ptr(), t->length(), 0);
+  }
 };
 
 /*************************************************************************/

sql/item_cmpfunc.cc

@@ -1970,14 +1970,14 @@ longlong Item_func_lt::val_int()
 longlong Item_func_strcmp::val_int()
 {
   DBUG_ASSERT(fixed == 1);
-  String *a=args[0]->val_str(&cmp.value1);
-  String *b=args[1]->val_str(&cmp.value2);
+  String *a= args[0]->val_str(&value1);
+  String *b= args[1]->val_str(&value2);
   if (!a || !b)
   {
     null_value=1;
     return 0;
   }
-  int value= sortcmp(a,b,cmp.cmp_collation.collation);
+  int value= cmp_collation.sortcmp(a, b);
   null_value=0;
   return !value ? 0 : (value < 0 ? (longlong) -1 : (longlong) 1);
 }

sql/item_cmpfunc.h

@@ -695,21 +695,18 @@ public:
 };
 
 
-class Item_func_strcmp :public Item_bool_func2
+class Item_func_strcmp :public Item_int_func
 {
+  String value1, value2;
+  DTCollation cmp_collation;
 public:
-  Item_func_strcmp(Item *a,Item *b) :Item_bool_func2(a,b) {}
+  Item_func_strcmp(Item *a,Item *b) :Item_int_func(a,b) {}
   longlong val_int();
-  optimize_type select_optimize() const { return OPTIMIZE_NONE; }
+  uint decimal_precision() const { return 1; }
   const char *func_name() const { return "strcmp"; }
-
-  virtual inline void print(String *str, enum_query_type query_type)
-  {
-    Item_func::print(str, query_type);
-  }
   void fix_length_and_dec()
   {
-    Item_bool_func2::fix_length_and_dec();
+    agg_arg_charsets_for_comparison(cmp_collation, args, 2);
     fix_char_length(2); // returns "1" or "0" or "-1"
   }
 };
@@ -803,6 +800,7 @@ public:
   Item_func_nullif(Item *a,Item *b)
     :Item_bool_func2(a,b), cached_result_type(INT_RESULT)
   {}
+  bool is_bool_func() { return false; }
   double val_real();
   longlong val_int();
   String *val_str(String *str);