MDEV-10191 non convertible chars convert() resulted in Null instead "?" on Windows

The problem was introduced by the patch for MDEV-7661,
which (in addition to the fix itself) included an attempt to make
CONVERT/CAST work in the same way with fields
(i.e. return NULL in strict mode if a non-convertable character found).
It appeared to be a bad idea and some users were affected by this
behavior change. Changing CONVERT/CAST not depend on sql_mode
(restoring pre-10.1.4 behavior).

mysql-test/r/ctype_utf8.result

@@ -1945,7 +1945,7 @@ Warnings:
 Warning	1300	Invalid utf8 character string: 'FD'
 select convert(char(0xff,0x8f) using utf8);
 convert(char(0xff,0x8f) using utf8)
-NULL
+??
 Warnings:
 Warning	1300	Invalid utf8 character string: '\xFF\x8F'
 select hex(convert(char(2557 using latin1) using utf8));
@@ -2114,7 +2114,7 @@ Warnings:
 Warning	1300	Invalid utf8 character string: 'FF'
 select hex(convert(0xFF using utf8));
 hex(convert(0xFF using utf8))
-NULL
+3F
 Warnings:
 Warning	1300	Invalid utf8 character string: '\xFF'
 select hex(_utf8 0x616263FF);
@@ -10473,5 +10473,30 @@ END
 DROP PROCEDURE p1;
 SET @@SQL_MODE=default;
 #
+# MDEV-10191 non convertible chars convert() resulted in Null instead "?" on Windows
+#
+SET sql_mode='STRICT_TRANS_TABLES';
+SELECT CONVERT(_utf8 0xC499 USING latin1);
+CONVERT(_utf8 0xC499 USING latin1)
+?
+Warnings:
+Warning	1977	Cannot convert 'utf8' character 0xC499 to 'latin1'
+SELECT CAST(_utf8 0xC499 AS CHAR CHARACTER SET latin1);
+CAST(_utf8 0xC499 AS CHAR CHARACTER SET latin1)
+?
+Warnings:
+Warning	1977	Cannot convert 'utf8' character 0xC499 to 'latin1'
+SET sql_mode=default;
+SELECT CONVERT(_utf8 0xC499 USING latin1);
+CONVERT(_utf8 0xC499 USING latin1)
+?
+Warnings:
+Warning	1977	Cannot convert 'utf8' character 0xC499 to 'latin1'
+SELECT CAST(_utf8 0xC499 AS CHAR CHARACTER SET latin1);
+CAST(_utf8 0xC499 AS CHAR CHARACTER SET latin1)
+?
+Warnings:
+Warning	1977	Cannot convert 'utf8' character 0xC499 to 'latin1'
+#
 # End of 10.1 tests
 #

mysql-test/r/ctype_utf8mb4.result

@@ -1970,7 +1970,7 @@ Warnings:
 Warning	1300	Invalid utf8mb4 character string: 'FD'
 select convert(char(0xff,0x8f) using utf8mb4);
 convert(char(0xff,0x8f) using utf8mb4)
-NULL
+??
 Warnings:
 Warning	1300	Invalid utf8mb4 character string: '\xFF\x8F'
 select hex(convert(char(2557 using latin1) using utf8mb4));
@@ -2139,7 +2139,7 @@ Warnings:
 Warning	1300	Invalid utf8mb4 character string: 'FF'
 select hex(convert(0xFF using utf8mb4));
 hex(convert(0xFF using utf8mb4))
-NULL
+3F
 Warnings:
 Warning	1300	Invalid utf8mb4 character string: '\xFF'
 select hex(_utf8mb4 0x616263FF);

mysql-test/r/ctype_utf8mb4_heap.result

@@ -1802,7 +1802,7 @@ Warnings:
 Warning	1300	Invalid utf8mb4 character string: 'FD'
 select convert(char(0xff,0x8f) using utf8mb4);
 convert(char(0xff,0x8f) using utf8mb4)
-NULL
+??
 Warnings:
 Warning	1300	Invalid utf8mb4 character string: '\xFF\x8F'
 select hex(convert(char(2557 using latin1) using utf8mb4));
@@ -1971,7 +1971,7 @@ Warnings:
 Warning	1300	Invalid utf8mb4 character string: 'FF'
 select hex(convert(0xFF using utf8mb4));
 hex(convert(0xFF using utf8mb4))
-NULL
+3F
 Warnings:
 Warning	1300	Invalid utf8mb4 character string: '\xFF'
 select hex(_utf8mb4 0x616263FF);

mysql-test/r/ctype_utf8mb4_innodb.result

@@ -1930,7 +1930,7 @@ Warnings:
 Warning	1300	Invalid utf8mb4 character string: 'FD'
 select convert(char(0xff,0x8f) using utf8mb4);
 convert(char(0xff,0x8f) using utf8mb4)
-NULL
+??
 Warnings:
 Warning	1300	Invalid utf8mb4 character string: '\xFF\x8F'
 select hex(convert(char(2557 using latin1) using utf8mb4));
@@ -2099,7 +2099,7 @@ Warnings:
 Warning	1300	Invalid utf8mb4 character string: 'FF'
 select hex(convert(0xFF using utf8mb4));
 hex(convert(0xFF using utf8mb4))
-NULL
+3F
 Warnings:
 Warning	1300	Invalid utf8mb4 character string: '\xFF'
 select hex(_utf8mb4 0x616263FF);

mysql-test/r/ctype_utf8mb4_myisam.result

@@ -1930,7 +1930,7 @@ Warnings:
 Warning	1300	Invalid utf8mb4 character string: 'FD'
 select convert(char(0xff,0x8f) using utf8mb4);
 convert(char(0xff,0x8f) using utf8mb4)
-NULL
+??
 Warnings:
 Warning	1300	Invalid utf8mb4 character string: '\xFF\x8F'
 select hex(convert(char(2557 using latin1) using utf8mb4));
@@ -2099,7 +2099,7 @@ Warnings:
 Warning	1300	Invalid utf8mb4 character string: 'FF'
 select hex(convert(0xFF using utf8mb4));
 hex(convert(0xFF using utf8mb4))
-NULL
+3F
 Warnings:
 Warning	1300	Invalid utf8mb4 character string: '\xFF'
 select hex(_utf8mb4 0x616263FF);

mysql-test/t/ctype_utf8.test

@@ -1983,6 +1983,18 @@ SET @@SQL_MODE=default;
 #DROP FUNCTION f1;
 #SET NAMES utf8;
 
+--echo #
+--echo # MDEV-10191 non convertible chars convert() resulted in Null instead "?" on Windows
+--echo #
+
+SET sql_mode='STRICT_TRANS_TABLES';
+SELECT CONVERT(_utf8 0xC499 USING latin1);
+SELECT CAST(_utf8 0xC499 AS CHAR CHARACTER SET latin1);
+
+SET sql_mode=default;
+SELECT CONVERT(_utf8 0xC499 USING latin1);
+SELECT CAST(_utf8 0xC499 AS CHAR CHARACTER SET latin1);
+
 
 --echo #
 --echo # End of 10.1 tests

sql/item.cc

@@ -5628,7 +5628,7 @@ String_copier_for_item::copy_with_warn(CHARSET_INFO *dstcs, String *dst,
                         srccs == &my_charset_bin ?
                         dstcs->csname : srccs->csname,
                         err.ptr());
-    return m_thd->is_strict_mode();
+    return false;
   }
   if (const char *pos= cannot_convert_error_pos())
   {
@@ -5641,7 +5641,7 @@ String_copier_for_item::copy_with_warn(CHARSET_INFO *dstcs, String *dst,
                         ER_CANNOT_CONVERT_CHARACTER,
                         ER_THD(m_thd, ER_CANNOT_CONVERT_CHARACTER),
                         srccs->csname, buf, dstcs->csname);
-    return m_thd->is_strict_mode();
+    return false;
   }
   return false;
 }

sql/item.h

@@ -548,8 +548,7 @@ class Item_func_not;
 class Item_splocal;
 
 /**
-  String_copier that honors the current sql_mode (strict vs non strict)
-  and can send warnings.
+  String_copier that sends Item specific warnings.
 */
 class String_copier_for_item: public String_copier
 {

sql/item_timefunc.cc

@@ -2396,7 +2396,7 @@ String *Item_char_typecast::copy(String *str, CHARSET_INFO *strcs)
   if (copier.copy_with_warn(cast_cs, &tmp_value, strcs,
                             str->ptr(), str->length(), cast_length))
   {
-    null_value= 1; // In strict mode: malformed data or could not convert
+    null_value= 1; // EOM
     return 0;
   }
   check_truncation_with_warn(str, copier.source_end_pos() - str->ptr());