Bug#58321 No warning when characters outside BMP0 is converted to UCS2

Problem: when inserting supplementary characters to an UCS2 column,
character was silently shrinked to 16-bit value.

Fix: produce a warning on attempt to insert a supplementary character,
and convert to question mark.

  @ mysql-test/r/ctype_many.result
  @ mysql-test/t/ctype_many.test
  Adding tests

  @ strings/ctype-ucs2.c
  Check if wc is greater than the highest value supported (0xFFFF),
  return MY_CS_ILUNI if true.

mysql-test/t/ctype_many.test

@@ -216,6 +216,10 @@ DROP TABLE t1;
 # End of 4.1 tests
 
 
+--echo #
+--echo # Start of 5.5 tests
+--echo #
+
 --echo #
 --echo # WL#1213 Implement 4-byte UTF8, UTF16 and UTF32
 --echo # Testing that only utf8mb4 is superset for utf8
@@ -284,3 +288,19 @@ SELECT CHARSET(CONCAT(utf32, utf8mb4)) FROM t1;
 SELECT CHARSET(CONCAT(utf32, utf16)) FROM t1;
 
 DROP TABLE t1;
+
+--echo #
+--echo # Bug#58321 No warning when characters outside BMP0 is converted to UCS2
+--echo #
+CREATE TABLE t1 (a VARCHAR(10) CHARACTER SET utf32);
+CREATE TABLE t2 (a VARCHAR(10) CHARACTER SET ucs2);
+INSERT INTO t1 VALUES (0x10082), (0x12345);
+INSERT INTO t2 SELECT * FROM t1;
+SELECT HEX(a) FROM t2;
+DROP TABLE t1;
+DROP TABLE t2;
+
+
+--echo #
+--echo # End of 5.5 tests
+--echo #

strings/ctype-ucs2.c

@@ -2693,7 +2693,10 @@ static int my_uni_ucs2(CHARSET_INFO *cs __attribute__((unused)) ,
 {
   if ( r+2 > e ) 
     return MY_CS_TOOSMALL2;
-  
+
+  if (wc > 0xFFFF) /* UCS2 does not support characters outside BMP */
+    return MY_CS_ILUNI;
+
   r[0]= (uchar) (wc >> 8);
   r[1]= (uchar) (wc & 0xFF);
   return 2;