MDEV-23497 fixup: Do not warn for ALTER TABLE conversion

Our intention is to make users aware that the ROW_FORMAT=COMPRESSED
format is on its way to deprecation.  It is an unnecessary annoyance
to users if we issue a warning when the user is converting a
ROW_FORMAT=COMPRESSED table to a supported format
(such as ROW_FORMAT=DYNAMIC).

ha_innobase::is_read_only(): Add a parameter to specify that an
ALTER TABLE to a supported format has been requested.

ha_innobase::check_if_supported_inplace_alter(): Set the parameter
when ALTER_OPTIONS to something else than ROW_FORMAT=COMPRESSED
(and without KEY_BLOCK_SIZE) is being requested.

Thanks to Elena Stepanova for suggesting this.

mysql-test/suite/innodb/r/default_row_format_compatibility.result

@@ -96,8 +96,6 @@ SELECT * FROM tab;
 a	b
 1	Check with max column size
 ALTER TABLE tab ROW_FORMAT=Dynamic;
-Warnings:
-Warning	4047	InnoDB refuses to write tables with ROW_FORMAT=COMPRESSED or KEY_BLOCK_SIZE.
 SET GLOBAL innodb_read_only_compressed=@save_innodb_read_only_compressed;
 SHOW TABLE STATUS LIKE 'tab';
 Name	Engine	Version	Row_format	Rows	Avg_row_length	Data_length	Max_data_length	Index_length	Data_free	Auto_increment	Create_time	Update_time	Check_time	Collation	Checksum	Create_options	Comment	Max_index_length	Temporary

storage/innobase/handler/ha_innodb.cc

@@ -7251,7 +7251,7 @@ ha_innobase::innobase_set_max_autoinc(
 }
 
 /** @return whether the table is read-only */
-bool ha_innobase::is_read_only() const
+bool ha_innobase::is_read_only(bool altering_to_supported) const
 {
   ut_ad(m_prebuilt->trx == thd_to_trx(m_user_thd));
 
@@ -7261,6 +7261,9 @@ bool ha_innobase::is_read_only() const
     return true;
   }
 
+  if (altering_to_supported)
+    return false;
+
   if (!DICT_TF_GET_ZIP_SSIZE(m_prebuilt->table->flags) ||
       !innodb_read_only_compressed)
     return false;

storage/innobase/handler/ha_innodb.h

@@ -458,7 +458,7 @@ class ha_innobase final : public handler
 	void reset_template();
 
 	/** @return whether the table is read-only */
-	bool is_read_only() const;
+	bool is_read_only(bool altering_to_supported= false) const;
 
 	inline void update_thd(THD* thd);
 	void update_thd();

storage/innobase/handler/handler0alter.cc

@@ -1988,7 +1988,11 @@ ha_innobase::check_if_supported_inplace_alter(
 
 	update_thd();
 
-	if (is_read_only()) {
+	if (is_read_only(!high_level_read_only
+			 && (ha_alter_info->handler_flags & ALTER_OPTIONS)
+			 && ha_alter_info->create_info->key_block_size == 0
+			 && ha_alter_info->create_info->row_type
+			 != ROW_TYPE_COMPRESSED)) {
 		ha_alter_info->unsupported_reason =
 			my_get_err_msg(ER_READ_ONLY_MODE);