MDEV-14293: MyRocks lacks basic functionality

The error
  "Unsupported collation on string indexed column %s Use
    binary collation (latin1_bin, binary, utf8_bin)."

is misleading. Change it:
- It is now a warning
- It is printed only for collations that do not support index-only access
  (reversible collations that use unpack_info are ok)
- The new warning text is:

  Indexed column %s.%s uses a collation that does not allow index-only
  access in secondary key and has reduced disk space efficiency
  in primary key.

sql/share/errmsg-utf8.txt

@@ -7753,3 +7753,6 @@ ER_GEOJSON_EMPTY_COORDINATES
 ER_MYROCKS_CANT_NOPAD_COLLATION
   eng "MyRocks doesn't currently support collations with \"No pad\" attribute."
 
+ER_MYROCKS_COLLATION_IS_LIMITED
+  eng "Indexed column %s.%s uses a collation that does not allow index-only access in secondary key and has reduced disk space efficiency in primary key."
+

storage/rocksdb/ha_rocksdb.cc

@@ -5957,9 +5957,11 @@ rdb_is_index_collation_supported(const my_core::Field *const field) {
   const my_core::enum_field_types type = field->real_type();
   /* Handle [VAR](CHAR|BINARY) or TEXT|BLOB */
   if (type == MYSQL_TYPE_VARCHAR || type == MYSQL_TYPE_STRING ||
-      type == MYSQL_TYPE_BLOB) {
-    return RDB_INDEX_COLLATIONS.find(field->charset()->number) !=
-           RDB_INDEX_COLLATIONS.end();
+      type == MYSQL_TYPE_BLOB)  {
+
+    return (RDB_INDEX_COLLATIONS.find(field->charset()->number) !=
+            RDB_INDEX_COLLATIONS.end()) ||
+            rdb_is_collation_supported(field->charset());
   }
   return true;
 }
@@ -6118,18 +6120,10 @@ int ha_rocksdb::create_cfs(
             !rdb_is_index_collation_supported(
                 table_arg->key_info[i].key_part[part].field) &&
             !rdb_collation_exceptions->matches(tablename_sys)) {
-          std::string collation_err;
-          for (const auto &coll : RDB_INDEX_COLLATIONS) {
-            if (collation_err != "") {
-              collation_err += ", ";
-            }
-            collation_err += get_charset_name(coll);
-          }
-          my_error(ER_UNSUPPORTED_COLLATION, MYF(0),
+
+          my_error(ER_MYROCKS_COLLATION_IS_LIMITED, MYF(ME_JUST_WARNING),
                    tbl_def_arg->full_tablename().c_str(),
-                   table_arg->key_info[i].key_part[part].field->field_name,
-                   collation_err.c_str());
-          DBUG_RETURN(HA_EXIT_FAILURE);
+                   table_arg->key_info[i].key_part[part].field->field_name);
         }
       }
     }

storage/rocksdb/mysql-test/rocksdb/r/add_index_inplace.result

@@ -279,8 +279,15 @@ DROP TABLE t1;
 set @tmp_rocksdb_strict_collation_check= @@rocksdb_strict_collation_check;
 set global rocksdb_strict_collation_check=1;
 CREATE TABLE t1 (a INT, b TEXT);
+# MariaDB no longer gives ER_UNSUPPORTED_COLLATION
 ALTER TABLE t1 ADD KEY kb(b(10));
-ERROR HY000: Unsupported collation on string indexed column test.t1.b Use binary collation (latin1_bin, binary, utf8_bin).
+ALTER TABLE t1 ADD PRIMARY KEY(a);
+DROP TABLE t1;
+CREATE TABLE t1 (a INT, b TEXT collate utf8_general_ci);
+# MariaDB no longer gives ER_UNSUPPORTED_COLLATION
+ALTER TABLE t1 ADD KEY kb(b(10));
+Warnings:
+Warning	4078	Indexed column test.t1.b uses a collation that does not allow index-only access in secondary key and has reduced disk space efficiency in primary key.
 ALTER TABLE t1 ADD PRIMARY KEY(a);
 DROP TABLE t1;
 set global rocksdb_strict_collation_check= @tmp_rocksdb_strict_collation_check;

storage/rocksdb/mysql-test/rocksdb/t/add_index_inplace.test

@@ -173,10 +173,17 @@ set @tmp_rocksdb_strict_collation_check= @@rocksdb_strict_collation_check;
 set global rocksdb_strict_collation_check=1;
 CREATE TABLE t1 (a INT, b TEXT);
 
---error ER_UNSUPPORTED_COLLATION
+--echo # MariaDB no longer gives ER_UNSUPPORTED_COLLATION
 ALTER TABLE t1 ADD KEY kb(b(10));
 ALTER TABLE t1 ADD PRIMARY KEY(a);
 DROP TABLE t1;
+
+CREATE TABLE t1 (a INT, b TEXT collate utf8_general_ci);
+--echo # MariaDB no longer gives ER_UNSUPPORTED_COLLATION
+ALTER TABLE t1 ADD KEY kb(b(10));
+ALTER TABLE t1 ADD PRIMARY KEY(a);
+DROP TABLE t1;
+
 set global rocksdb_strict_collation_check= @tmp_rocksdb_strict_collation_check;
 
 # make sure race condition between connection close and alter on another

storage/rocksdb/rdb_datadic.cc

@@ -2921,7 +2921,7 @@ std::array<const Rdb_collation_codec *, MY_ALL_CHARSETS_SIZE>
     rdb_collation_data;
 mysql_mutex_t rdb_collation_data_mutex;
 
-static bool rdb_is_collation_supported(const my_core::CHARSET_INFO *const cs) {
+bool rdb_is_collation_supported(const my_core::CHARSET_INFO *const cs) {
   return cs->strxfrm_multiply==1 && cs->mbmaxlen == 1 &&
          !(cs->state & (MY_CS_BINSORT | MY_CS_NOPAD));
 }

storage/rocksdb/rdb_datadic.h

@@ -1358,4 +1358,6 @@ struct Rdb_index_info {
   uint64 m_ttl_duration = 0;
 };
 
+bool rdb_is_collation_supported(const my_core::CHARSET_INFO *const cs);
+
 } // namespace myrocks