MDEV-20425: Fix -Wimplicit-fallthrough

With --skip-debug-assert, DBUG_ASSERT(false) will allow execution to
continue. Hence, we will need /* fall through */ after them.

Some DBUG_ASSERT(0) were replaced by break; when the switch () statement
was followed by DBUG_ASSERT(0).

sql/create_options.cc

@@ -1,4 +1,4 @@
-/* Copyright (C) 2010, 2017, MariaDB Corporation Ab
+/* Copyright (C) 2010, 2019, MariaDB Corporation.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -132,7 +132,8 @@ static bool set_one_value(ha_create_table_option *opt,
   switch (opt->type)
   {
   case HA_OPTION_TYPE_SYSVAR:
-    DBUG_ASSERT(0); // HA_OPTION_TYPE_SYSVAR's are replaced in resolve_sysvars()
+    // HA_OPTION_TYPE_SYSVAR's are replaced in resolve_sysvars()
+    break; // to DBUG_ASSERT(0)
   case HA_OPTION_TYPE_ULL:
     {
       ulonglong *val= (ulonglong*)value_ptr(base, opt);

sql/field.h

@@ -1,7 +1,7 @@
 #ifndef FIELD_INCLUDED
 #define FIELD_INCLUDED
 /* Copyright (c) 2000, 2015, Oracle and/or its affiliates.
-   Copyright (c) 2008, 2017, MariaDB Corporation.
+   Copyright (c) 2008, 2019, MariaDB Corporation.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -461,6 +461,7 @@ inline bool is_temporal_type_with_date(enum_field_types type)
   case MYSQL_TYPE_DATETIME2:
   case MYSQL_TYPE_TIMESTAMP2:
     DBUG_ASSERT(0); // field->real_type() should not get to here.
+    /* fall through */
   default:
     return false;
   }

sql/sql_lex.cc

@@ -2911,6 +2911,7 @@ void st_select_lex_unit::print(String *str, enum_query_type query_type)
       {
       default:
         DBUG_ASSERT(0);
+        /* fall through */
       case UNION_TYPE:
         str->append(STRING_WITH_LEN(" union "));
         if (union_all)

sql/sql_parse.cc

@@ -3579,6 +3579,7 @@ mysql_execute_command(THD *thd)
         case GET_NO_ARG:
         case GET_DISABLED:
           DBUG_ASSERT(0);
+          /* fall through */
         case 0:
         case GET_FLAGSET:
         case GET_ENUM:

sql/sql_show.cc

@@ -2569,6 +2569,7 @@ static const LEX_CSTRING *view_algorithm(TABLE_LIST *table)
     return &merge;
   default:
     DBUG_ASSERT(0); // never should happen
+    /* fall through */
   case VIEW_ALGORITHM_UNDEFINED:
     return &undefined;
   }

sql/table.cc

@@ -9114,7 +9114,7 @@ bool vers_select_conds_t::eq(const vers_select_conds_t &conds) const
   case SYSTEM_TIME_ALL:
     return true;
   case SYSTEM_TIME_BEFORE:
-    DBUG_ASSERT(0);
+    break;
   case SYSTEM_TIME_AS_OF:
     return start.eq(conds.start);
   case SYSTEM_TIME_FROM_TO:

storage/innobase/fil/fil0fil.cc

@@ -826,6 +826,7 @@ static void fil_flush_low(fil_space_t* space, bool metadata = false)
 		switch (space->purpose) {
 		case FIL_TYPE_TEMPORARY:
 			ut_ad(0); // we already checked for this
+			/* fall through */
 		case FIL_TYPE_TABLESPACE:
 		case FIL_TYPE_IMPORT:
 			fil_n_pending_tablespace_flushes++;

storage/innobase/handler/handler0alter.cc

@@ -2135,7 +2135,7 @@ innobase_col_to_mysql(
 	case DATA_SYS:
 		/* These column types should never be shipped to MySQL. */
 		ut_ad(0);
-
+		/* fall through */
 	case DATA_FLOAT:
 	case DATA_DOUBLE:
 	case DATA_DECIMAL:

storage/innobase/mtr/mtr0mtr.cc

@@ -754,7 +754,7 @@ mtr_t::Command::prepare_write()
 	switch (m_impl->m_log_mode) {
 	case MTR_LOG_SHORT_INSERTS:
 		ut_ad(0);
-		/* fall through (write no redo log) */
+		/* fall through */
 	case MTR_LOG_NO_REDO:
 	case MTR_LOG_NONE:
 		ut_ad(m_impl->m_log.size() == 0);

storage/innobase/row/row0log.cc

@@ -1790,6 +1790,7 @@ row_log_table_apply_insert(
 		break;
 	default:
 		ut_ad(0);
+		/* fall through */
 	case DB_INVALID_NULL:
 		ut_ad(row == NULL);
 		return(error);
@@ -2078,6 +2079,7 @@ row_log_table_apply_update(
 		break;
 	default:
 		ut_ad(0);
+		/* fall through */
 	case DB_INVALID_NULL:
 		ut_ad(row == NULL);
 		return(error);

storage/innobase/row/row0uins.cc

@@ -1,7 +1,7 @@
 /*****************************************************************************
 
 Copyright (c) 1997, 2017, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2017, 2018, MariaDB Corporation.
+Copyright (c) 2017, 2019, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -583,6 +583,7 @@ row_undo_ins(
 	switch (node->rec_type) {
 	default:
 		ut_ad(!"wrong undo record type");
+		/* fall through */
 	case TRX_UNDO_INSERT_REC:
 		/* Skip the clustered index (the first index) */
 		node->index = dict_table_get_next_index(node->index);