MDEV-30805 SIGSEGV in my_convert and UBSAN: member access within null pointer of type 'const struct MY_CHARSET_HANDLER' in my_convert

Type_handler::partition_field_append_value() erroneously
passed the address of my_collation_contextually_typed_binary
to conversion functions copy_and_convert() and my_convert().

This happened because generate_partition_syntax_for_frm()
was called from mysql_create_frm_image() in the stage when
the fields in List<Create_field> can still contain unresolved
contextual collations, like "binary" in the reported crash scenario:

  ALTER TABLE t CHANGE COLUMN a a CHAR BINARY;

Fix:

1. Splitting mysql_prepare_create_table() into two parts:
   - mysql_prepare_create_table_stage1() interates through
     List<Create_field> and calls Create_field::prepare_stage1(),
     which performs basic attribute initialization, including
     context collation resolution.
   - mysql_prepare_create_table_finalize() - the rest of the
     old mysql_prepare_create_table() code.

2. Changing mysql_create_frm_image():
   It now calls:
   - mysql_prepare_create_table_stage1() in the very
     beginning, before the partition related code.
   - mysql_prepare_create_table_finalize() in the end,
    instead of the old mysql_prepare_create_table() call

3. Adding mysql_prepare_create_table() as a wrapper
   for two calls:
     mysql_prepare_create_table_stage1() ||
     mysql_prepare_create_table_finalize()
   so the code stays unchanged in the other places
   where mysql_prepare_create_table() was used.

4. Changing prototype for Type_handler::Column_definition_prepare_stage1()
   Removing arguments:
   - handler *file
   - ulonglong table_flags
   Adding a new argument instead:
   - column_definition_type_t type
   This allows to call Column_definition_prepare_stage1() and
   therefore to call mysql_prepare_create_table_stage1()
   before instantiation of a handler.
   This simplifies the code, because in case of a partitioned table,
   mysql_create_frm_image() creates a handler of the underlying
   partition first, the frees it and created a ha_partition
   instance instead.
   mysql_prepare_create_table() before the fix was called with the final
   (ha_partition) handler.

5. Moving parts of Column_definition_prepare_stage1() which
   need a pointer to handler and table_flags to
   Column_definition_prepare_stage2().

3 files changed, 42 insertions, 1 deletions

diff --git a/mysql-test/main/partition_charset.result b/mysql-test/main/partition_charset.result
index f8f75e8bee7..a0019dd8fc3 100644
--- a/mysql-test/main/partition_charset.result
+++ b/mysql-test/main/partition_charset.result
@@ -20,3 +20,24 @@ create table t1 (a varchar(1), primary key (a))
 partition by list (ascii(a))
 (partition p1 values in (65));
 ERROR HY000: This partition function is not allowed
+#
+# Start of 10.9 tests
+#
+#
+# MDEV-30805 SIGSEGV in my_convert and UBSAN: member access within null pointer of type 'const struct MY_CHARSET_HANDLER' in my_convert
+#
+CREATE TABLE t1 (a CHAR CHARACTER SET ucs2)
+PARTITION BY RANGE COLUMNS (a)
+(PARTITION p0 VALUES LESS THAN ('a'));
+ALTER TABLE t1 CHANGE COLUMN a a CHAR BINARY;
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` char(1) CHARACTER SET latin1 COLLATE latin1_bin DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+ PARTITION BY RANGE  COLUMNS(`a`)
+(PARTITION `p0` VALUES LESS THAN ('a') ENGINE = MyISAM)
+DROP TABLE t1;
+#
+# End of 10.9 tests
+#
diff --git a/mysql-test/main/partition_charset.test b/mysql-test/main/partition_charset.test
index 6842e5268fa..b8a17ce4fca 100644
--- a/mysql-test/main/partition_charset.test
+++ b/mysql-test/main/partition_charset.test
@@ -27,3 +27,23 @@ partition by list (ascii(a))
 #insert into t1 values ('A');
 #replace into t1 values ('A');
 #drop table t1;
+
+--echo #
+--echo # Start of 10.9 tests
+--echo #
+
+--echo #
+--echo # MDEV-30805 SIGSEGV in my_convert and UBSAN: member access within null pointer of type 'const struct MY_CHARSET_HANDLER' in my_convert
+--echo #
+
+CREATE TABLE t1 (a CHAR CHARACTER SET ucs2)
+  PARTITION BY RANGE COLUMNS (a)
+  (PARTITION p0 VALUES LESS THAN ('a'));
+ALTER TABLE t1 CHANGE COLUMN a a CHAR BINARY;
+SHOW CREATE TABLE t1;
+DROP TABLE t1;
+
+--echo #
+--echo # End of 10.9 tests
+--echo #
+
diff --git a/mysql-test/main/partition_utf8-debug.result b/mysql-test/main/partition_utf8-debug.result
index db1396198ab..2b4982a3dcc 100644
--- a/mysql-test/main/partition_utf8-debug.result
+++ b/mysql-test/main/partition_utf8-debug.result
@@ -77,7 +77,7 @@ CREATE OR REPLACE TABLE t1 (a DATE) CHARACTER SET utf8
 PARTITION BY LIST COLUMNS (a) (PARTITION p0 VALUES IN (FROM_DAYS(100)));
 Warnings:
 Note	1003	 PARTITION BY LIST  COLUMNS(`a`)
-(PARTITION `p0` VALUES IN (_utf8mb3 0x303030302d30302d3030) ENGINE = MyISAM)
+(PARTITION `p0` VALUES IN (_latin1 0x303030302d30302d3030) ENGINE = MyISAM)
 SELECT PARTITION_DESCRIPTION FROM INFORMATION_SCHEMA.PARTITIONS WHERE TABLE_NAME='t1';
 PARTITION_DESCRIPTION
 '0000-00-00'