This reverts commit e86010f909fb6b8c4ffd9d6df92991ac079e67e7.
Reverting on Monty's request, as this change makes merging
things from 10.5 to 10.2 much harder.
Fix the build on clang. GCC only checks that a member function with
the C++11 override keyword is actually overriding a virtual member
function in a base class. In clang, you will get a warning for
overridden member functions that lack the keyword, if any overridden
member function of the class is declared with the keyword.
This patch fixes:
- MDEV-19284 INSTANT ALTER with ucs2-to-utf16 conversion produces bad data
- MDEV-19285 INSTANT ALTER from ascii_general_ci to latin1_general_ci produces corrupt data
These regressions were introduced in 10.4.3 by:
- MDEV-15564 Avoid table rebuild in ALTER TABLE on collation or charset changes
Changes:
1. Cleanup: Adding a helper method
Field_longstr::csinfo_change_allows_instant_alter(),
to remove some duplicate code in field.cc.
2. Cleanup: removing Type_handler::Charsets_are_compatible() and static
function charsets_are_compatible() and
introducing new methods in the recently added class Charset instead:
- encoding_allows_reinterpret_as()
- encoding_and_order_allow_reinterpret_as()
3. Bug fix: Removing the code that allowed instant conversion for
ascii-to->8bit and ucs2-to->utf16.
This actually fixes MDEV-19284 and MDEV-19285.
4. Bug fix: Adding a helper method Charset::collation_specific_name().
The old corresponding code in Type_handler::Charsets_are_compatible()
was not safe against (badly named) user-defined collations whose
character set name can be longer than collation name.
This also fixes:
MDEV-17299 Assertion `maybe_null' failed in make_sortkey
Note, during merge of the 10.1 version of MDEV-17299,
please use the 10.3 version of the code (i.e. null merge the 10.1 version).
sql_field->key_length was 0 for blob fields when a field was
being added, but Field_blob::character_octet_length() on
subsequent ALTER TABLE's (when the Field object in the old table
already existed). This means mysql_prepare_create_table() couldn't
reliably detect if the keyseg was a prefix.
1. Renaming Type_handler_json to Type_handler_json_longtext
There will be other JSON handlers soon, e.g. Type_handler_json_varchar.
2. Making the code more symmetric for data types:
- Adding a new virtual method
Type_handler::Column_definition_validate_check_constraint()
- Moving JSON-specific code from sql_yacc.yy to
Type_handler_json_longtext::Column_definition_validate_check_constraint()
3. Adding new files sql_type_json.cc and sql_type_json.h
and moving Type_handler+JSON related code into these files.
