MDEV-10386 Assertion `fixed == 1' failed in virtual String* Item_func_conv_charset::val_str(String*)

The patch b96c196f1c added a new call for
safe_charset_converter() without a corresponding fix_fields().
In case of a sub-query the created Item remained in non-fixed state.
The problem did not show up with literal derived expressions, only
subselects were affected. This patch adds a corresponding fix_fields()
to the previously added safe_charset_converter().

mysql-test/r/subselect.result

@@ -7105,3 +7105,14 @@ group by round((select 1 from t1 limit 1));
 round((select 1 from t1 limit 1))
 1
 drop table t1;
+#
+# MDEV-10386 Assertion `fixed == 1' failed in virtual String* Item_func_conv_charset::val_str(String*)
+#
+CREATE TABLE t1 (f1 CHAR(3) CHARACTER SET utf8 NULL, f2 CHAR(3) CHARACTER SET latin1 NULL);
+INSERT INTO t1 VALUES ('foo','bar');
+SELECT * FROM t1 WHERE f2 >= SOME ( SELECT f1 FROM t1 );
+f1	f2
+SELECT * FROM t1 WHERE f2 <= SOME ( SELECT f1 FROM t1 );
+f1	f2
+foo	bar
+DROP TABLE t1;

mysql-test/r/subselect_no_mat.result

@@ -7102,6 +7102,17 @@ group by round((select 1 from t1 limit 1));
 round((select 1 from t1 limit 1))
 1
 drop table t1;
+#
+# MDEV-10386 Assertion `fixed == 1' failed in virtual String* Item_func_conv_charset::val_str(String*)
+#
+CREATE TABLE t1 (f1 CHAR(3) CHARACTER SET utf8 NULL, f2 CHAR(3) CHARACTER SET latin1 NULL);
+INSERT INTO t1 VALUES ('foo','bar');
+SELECT * FROM t1 WHERE f2 >= SOME ( SELECT f1 FROM t1 );
+f1	f2
+SELECT * FROM t1 WHERE f2 <= SOME ( SELECT f1 FROM t1 );
+f1	f2
+foo	bar
+DROP TABLE t1;
 set optimizer_switch=default;
 select @@optimizer_switch like '%materialization=on%';
 @@optimizer_switch like '%materialization=on%'

mysql-test/r/subselect_no_opts.result

@@ -7100,4 +7100,15 @@ group by round((select 1 from t1 limit 1));
 round((select 1 from t1 limit 1))
 1
 drop table t1;
+#
+# MDEV-10386 Assertion `fixed == 1' failed in virtual String* Item_func_conv_charset::val_str(String*)
+#
+CREATE TABLE t1 (f1 CHAR(3) CHARACTER SET utf8 NULL, f2 CHAR(3) CHARACTER SET latin1 NULL);
+INSERT INTO t1 VALUES ('foo','bar');
+SELECT * FROM t1 WHERE f2 >= SOME ( SELECT f1 FROM t1 );
+f1	f2
+SELECT * FROM t1 WHERE f2 <= SOME ( SELECT f1 FROM t1 );
+f1	f2
+foo	bar
+DROP TABLE t1;
 set @optimizer_switch_for_subselect_test=null;

mysql-test/r/subselect_no_scache.result

@@ -7111,6 +7111,17 @@ group by round((select 1 from t1 limit 1));
 round((select 1 from t1 limit 1))
 1
 drop table t1;
+#
+# MDEV-10386 Assertion `fixed == 1' failed in virtual String* Item_func_conv_charset::val_str(String*)
+#
+CREATE TABLE t1 (f1 CHAR(3) CHARACTER SET utf8 NULL, f2 CHAR(3) CHARACTER SET latin1 NULL);
+INSERT INTO t1 VALUES ('foo','bar');
+SELECT * FROM t1 WHERE f2 >= SOME ( SELECT f1 FROM t1 );
+f1	f2
+SELECT * FROM t1 WHERE f2 <= SOME ( SELECT f1 FROM t1 );
+f1	f2
+foo	bar
+DROP TABLE t1;
 set optimizer_switch=default;
 select @@optimizer_switch like '%subquery_cache=on%';
 @@optimizer_switch like '%subquery_cache=on%'

mysql-test/r/subselect_no_semijoin.result

@@ -7100,5 +7100,16 @@ group by round((select 1 from t1 limit 1));
 round((select 1 from t1 limit 1))
 1
 drop table t1;
+#
+# MDEV-10386 Assertion `fixed == 1' failed in virtual String* Item_func_conv_charset::val_str(String*)
+#
+CREATE TABLE t1 (f1 CHAR(3) CHARACTER SET utf8 NULL, f2 CHAR(3) CHARACTER SET latin1 NULL);
+INSERT INTO t1 VALUES ('foo','bar');
+SELECT * FROM t1 WHERE f2 >= SOME ( SELECT f1 FROM t1 );
+f1	f2
+SELECT * FROM t1 WHERE f2 <= SOME ( SELECT f1 FROM t1 );
+f1	f2
+foo	bar
+DROP TABLE t1;
 set @optimizer_switch_for_subselect_test=null;
 set @join_cache_level_for_subselect_test=NULL;

mysql-test/t/subselect.test

@@ -5988,3 +5988,13 @@ from t1
 group by round((select 1 from t1 limit 1));
 
 drop table t1;
+
+--echo #
+--echo # MDEV-10386 Assertion `fixed == 1' failed in virtual String* Item_func_conv_charset::val_str(String*)
+--echo #
+
+CREATE TABLE t1 (f1 CHAR(3) CHARACTER SET utf8 NULL, f2 CHAR(3) CHARACTER SET latin1 NULL);
+INSERT INTO t1 VALUES ('foo','bar');
+SELECT * FROM t1 WHERE f2 >= SOME ( SELECT f1 FROM t1 );
+SELECT * FROM t1 WHERE f2 <= SOME ( SELECT f1 FROM t1 );
+DROP TABLE t1;

sql/item.cc

@@ -1164,7 +1164,8 @@ Item *Item_cache::safe_charset_converter(CHARSET_INFO *tocs)
   if (conv == example)
     return this;
   Item_cache *cache;
-  if (!conv || !(cache= new Item_cache_str(conv)))
+  if (!conv || conv->fix_fields(current_thd, (Item **) NULL) ||
+      !(cache= new Item_cache_str(conv)))
     return NULL; // Safe conversion is not possible, or OEM
   cache->setup(conv);
   cache->fixed= false; // Make Item::fix_fields() happy