MDEV-20856 Bad values in metadata views for partitions on VARBINARY

The old code to print partition values was too complicated:
- it created new Items for character set conversion purposes.
- it mixed string conversion and partition error reporting
  in the same code blocks.

Simplifying the code as follows:

- Adding helper methods String::can_be_safely_convert_to() and
  String::append_introducer_and_hex().

- Adding DBUG_EXECUTE_IF("generate_partition_syntax_for_frm",  push_warning...)
  into generate_partition_syntax_for_frm(), to test the PARTITON
  clause written to FRM. Adding test partition_utf8-debug.test for this.

- Removing functions get_cs_converted_part_value_from_string() and
  get_cs_converted_string_value. Changing get_partition_column_description()
  to use Type_handler::partition_field_append_value() instead.
  This makes SHOW CREATE TABLE and SELECT FROM I_S.PARTITIONS
  use the same code path.

- Changing Type_handler::partition_field_append_value() not to
  call convert_charset_partition_constant(), to avoid creating a new Item
  for string conversion pursposes.
  Rewritting the code to use only String methods.

- Removing error reporting code (ER_PARTITION_FUNCTION_IS_NOT_ALLOWED)
  from Type_handler::partition_field_append_value().
  The error is correctly detected and reported on the caller level.
  So error reporting was redundant here.

Also:

- Moving methods Type_handler::partition_field_*() from sql_partition.cc
  to sql_type.cc. This fixes compilation problem with -DPLUGIN_PARTITION=NO,
  earlier introduced by the patch for MDEV-20831.

1 files changed, 88 insertions, 0 deletions

diff --git a/mysql-test/main/partition_utf8-debug.result b/mysql-test/main/partition_utf8-debug.result
new file mode 100644
index 00000000000..569bec3ea8a
--- /dev/null
+++ b/mysql-test/main/partition_utf8-debug.result
@@ -0,0 +1,88 @@
+#
+# Start of 10.5 tests
+#
+#
+# MDEV-20856 Bad values in metadata views for partitions on VARBINARY
+#
+SET NAMES utf8;
+SET @save_dbug = @@debug_dbug;
+SET SESSION debug_dbug="+d,generate_partition_syntax_for_frm";
+CREATE OR REPLACE TABLE t1 (a VARCHAR(10)) CHARACTER SET latin1
+PARTITION BY LIST COLUMNS (a) (PARTITION p0 VALUES IN (_utf8'Ṡ'));
+ERROR HY000: This partition function is not allowed
+CREATE OR REPLACE TABLE t1 (a VARCHAR(10)) CHARACTER SET latin1
+PARTITION BY LIST COLUMNS (a) (PARTITION p0 VALUES IN ('Ṡ'));
+ERROR HY000: This partition function is not allowed
+CREATE OR REPLACE TABLE t1 (a VARCHAR(10)) CHARACTER SET latin1
+PARTITION BY LIST COLUMNS (a) (PARTITION p0 VALUES IN (_latin1 0xDF));
+Warnings:
+Note	1003	 PARTITION BY LIST  COLUMNS(`a`)
+(PARTITION `p0` VALUES IN (_latin1 0xdf) ENGINE = MyISAM)
+SELECT PARTITION_DESCRIPTION FROM INFORMATION_SCHEMA.PARTITIONS WHERE TABLE_NAME='t1';
+PARTITION_DESCRIPTION
+'ß'
+DROP TABLE t1;
+CREATE OR REPLACE TABLE t1 (a VARCHAR(10)) CHARACTER SET latin1
+PARTITION BY LIST COLUMNS (a) (PARTITION p0 VALUES IN (_utf8'ß'));
+Warnings:
+Note	1003	 PARTITION BY LIST  COLUMNS(`a`)
+(PARTITION `p0` VALUES IN (_latin1 0xdf) ENGINE = MyISAM)
+SELECT PARTITION_DESCRIPTION FROM INFORMATION_SCHEMA.PARTITIONS WHERE TABLE_NAME='t1';
+PARTITION_DESCRIPTION
+'ß'
+DROP TABLE t1;
+CREATE OR REPLACE TABLE t1 (a VARCHAR(10)) CHARACTER SET latin1
+PARTITION BY LIST COLUMNS (a) (PARTITION p0 VALUES IN ('ß'));
+Warnings:
+Note	1003	 PARTITION BY LIST  COLUMNS(`a`)
+(PARTITION `p0` VALUES IN (_latin1 0xdf) ENGINE = MyISAM)
+DROP TABLE t1;
+CREATE OR REPLACE TABLE t1 (a VARCHAR(10)) CHARACTER SET utf8
+PARTITION BY LIST COLUMNS (a) (PARTITION p0 VALUES IN (_utf8'ß'));
+Warnings:
+Note	1003	 PARTITION BY LIST  COLUMNS(`a`)
+(PARTITION `p0` VALUES IN (_utf8 0xc39f) ENGINE = MyISAM)
+SELECT PARTITION_DESCRIPTION FROM INFORMATION_SCHEMA.PARTITIONS WHERE TABLE_NAME='t1';
+PARTITION_DESCRIPTION
+'ß'
+DROP TABLE t1;
+CREATE OR REPLACE TABLE t1 (a VARCHAR(10)) CHARACTER SET utf8
+PARTITION BY LIST COLUMNS (a) (PARTITION p0 VALUES IN ('ß'));
+Warnings:
+Note	1003	 PARTITION BY LIST  COLUMNS(`a`)
+(PARTITION `p0` VALUES IN (_utf8 0xc39f) ENGINE = MyISAM)
+SELECT PARTITION_DESCRIPTION FROM INFORMATION_SCHEMA.PARTITIONS WHERE TABLE_NAME='t1';
+PARTITION_DESCRIPTION
+'ß'
+DROP TABLE t1;
+CREATE OR REPLACE TABLE t1 (a VARBINARY(10)) CHARACTER SET utf8
+PARTITION BY LIST COLUMNS (a) (PARTITION p0 VALUES IN (0xFF));
+Warnings:
+Note	1003	 PARTITION BY LIST  COLUMNS(`a`)
+(PARTITION `p0` VALUES IN (_binary 0xff) ENGINE = MyISAM)
+SELECT PARTITION_DESCRIPTION FROM INFORMATION_SCHEMA.PARTITIONS WHERE TABLE_NAME='t1';
+PARTITION_DESCRIPTION
+_binary 0xff
+DROP TABLE t1;
+CREATE OR REPLACE TABLE t1 (a DATE) CHARACTER SET utf8
+PARTITION BY LIST COLUMNS (a) (PARTITION p0 VALUES IN (FROM_DAYS(NULL)));
+Warnings:
+Note	1003	 PARTITION BY LIST  COLUMNS(`a`)
+(PARTITION `p0` VALUES IN (NULL) ENGINE = MyISAM)
+SELECT PARTITION_DESCRIPTION FROM INFORMATION_SCHEMA.PARTITIONS WHERE TABLE_NAME='t1';
+PARTITION_DESCRIPTION
+NULL
+DROP TABLE t1;
+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 (_utf8 0x303030302d30302d3030) ENGINE = MyISAM)
+SELECT PARTITION_DESCRIPTION FROM INFORMATION_SCHEMA.PARTITIONS WHERE TABLE_NAME='t1';
+PARTITION_DESCRIPTION
+'0000-00-00'
+DROP TABLE t1;
+SET debug_dbug=@save_dbug;
+#
+# End of 10.5 tests
+#