open frm for DROP TABLE

needed to get partitioning and information about
secondary objects

mysql-test/main/features.result

@@ -176,7 +176,7 @@ create table t2 (b int, constraint foo check (b < 10));
 drop table t1, t2;
 show status like "feature_check_constraint";
 Variable_name	Value
-Feature_check_constraint	2
+Feature_check_constraint	4
 #
 # Feature insert...returning
 #

mysql-test/main/invisible_field.result

@@ -444,7 +444,7 @@ d	int(11)	YES	UNI	NULL
 drop table t1;
 SHOW STATUS LIKE 'Feature_invisible_columns';
 Variable_name	Value
-Feature_invisible_columns	52
+Feature_invisible_columns	54
 #invisible is non reserved
 create table t1(a int unique , invisible int invisible, c int );
 desc t1;

mysql-test/suite/archive/discover.result

@@ -93,7 +93,7 @@ drop table t0;
 db.opt
 show status like 'Handler_discover';
 Variable_name	Value
-Handler_discover	6
+Handler_discover	7
 #
 # Bug#45377: ARCHIVE tables aren't discoverable after OPTIMIZE
 #

sql/sql_class.h

@@ -1324,6 +1324,13 @@ class Query_arena
   {
     return strmake_lex_cstring(from.str, from.length);
   }
+  LEX_CUSTRING strmake_lex_custring(const LEX_CUSTRING &from) const
+  {
+    const void *tmp= memdup(from.str, from.length);
+    if (!tmp)
+      return {0,0};
+    return {(const uchar*)tmp, from.length};
+  }
   LEX_CSTRING strmake_lex_cstring_trim_whitespace(const LEX_CSTRING &from,
                                                   CHARSET_INFO *cs)
   {

sql/sql_table.cc

@@ -1265,6 +1265,7 @@ static uint32 get_comment(THD *thd, uint32 comment_pos,
   return 0;
 }
 
+
 /**
   Execute the drop of a sequence, view or table (normal or temporary).
 
@@ -1535,20 +1536,52 @@ int mysql_rm_table_no_locks(THD *thd, TABLE_LIST *tables,
 
     cpath = { path, (size_t)(path_end - path) };
 
+    Dummy_error_handler err_handler;
+    thd->push_internal_handler(&err_handler);
+    if (TABLE_SHARE *share= tdc_acquire_share(thd, table, GTS_TABLE))
+    {
+      table_type= share->table_type;
+      hton= plugin_hton(plugin_lock(thd, share->db_plugin));
+      version= thd->strmake_lex_custring(share->tabledef_version);
+      if (share->default_part_plugin)
+        partition_engine_name=
+          thd->strmake_lex_cstring(*plugin_name(share->default_part_plugin));
+      tdc_release_share(share);
+    }
+    else
+    {
+      switch (err_handler.got_error()) {
+      case ER_WRONG_OBJECT:
+        table_type= TABLE_TYPE_VIEW;
+        break;
+      case ER_NO_SUCH_TABLE: /* no .frm */
+        table_type= TABLE_TYPE_UNKNOWN;
+        break;
+      case ER_NOT_FORM_FILE:
       {
+        /*
+          cannot open the frm, let's at least get the engine
+          see main.partition_not_blackhole and connect.drop-open-error
+        */
         char engine_buf[NAME_CHAR_LEN + 1];
         LEX_CSTRING engine= { engine_buf, 0 };
-
-      table_type= dd_frm_type(thd, path, &engine, &partition_engine_name,
-                              &version);
+        table_type= dd_frm_type(thd, path, &engine, NULL, &version);
         if (table_type == TABLE_TYPE_NORMAL || table_type == TABLE_TYPE_SEQUENCE)
         {
           plugin_ref p= plugin_lock_by_name(thd, &engine,
                                            MYSQL_STORAGE_ENGINE_PLUGIN);
           hton= p ? plugin_hton(p) : NULL;
         }
-      // note that for TABLE_TYPE_VIEW and TABLE_TYPE_UNKNOWN hton == NULL
+        break;
+      }
+      case ER_FAILED_READ_FROM_PAR_FILE: /* no .par file */
+        hton= partition_hton;
+        /* fall through */
+      default: /* unreadable (corrupted?) .frm, still need to DROP it */
+        table_type= TABLE_TYPE_NORMAL;
+      }
     }
+    thd->pop_internal_handler();
 
     thd->replication_flags= 0;
     const bool was_view= table_type == TABLE_TYPE_VIEW;