MDEV-31986 Remove old check_db_name() from make_table_name_list()

- Replacing the old style inplace check_db_name() in make_table_name_list()
  to the new style non-modifying code
- Adding "const" qualifier to the "db" parameter to ha_discover_table_names()
  and its dependency functions.

sql/handler.cc

@@ -532,7 +532,8 @@ static int full_discover_for_existence(handlerton *, const char *, const char *)
 static int ext_based_existence(handlerton *, const char *, const char *)
 { return 0; }
 
-static int hton_ext_based_table_discovery(handlerton *hton, LEX_CSTRING *db,
+static int hton_ext_based_table_discovery(handlerton *hton,
+                             const LEX_CSTRING *db,
                              MY_DIR *dir, handlerton::discovered_list *result)
 {
   /*
@@ -6679,7 +6680,7 @@ void Discovered_table_list::remove_duplicates()
 
 struct st_discover_names_args
 {
-  LEX_CSTRING *db;
+  const LEX_CSTRING *db;
   MY_DIR *dirp;
   Discovered_table_list *result;
   uint possible_duplicates;
@@ -6724,7 +6725,7 @@ static my_bool discover_names(THD *thd, plugin_ref plugin,
   for DROP DATABASE (as it needs to know and delete non-table files).
 */
 
-int ha_discover_table_names(THD *thd, LEX_CSTRING *db, MY_DIR *dirp,
+int ha_discover_table_names(THD *thd, const LEX_CSTRING *db, MY_DIR *dirp,
                             Discovered_table_list *result, bool reusable)
 {
   int error;

sql/handler.h

@@ -1621,7 +1621,8 @@ struct handlerton
 
      Returns 0 on success and 1 on error.
    */
-   int (*discover_table_names)(handlerton *hton, LEX_CSTRING *db, MY_DIR *dir,
+   int (*discover_table_names)(handlerton *hton, const LEX_CSTRING *db,
+                               MY_DIR *dir,
                                discovered_list *result);
 
    /*
@@ -5574,7 +5575,7 @@ class Discovered_table_list: public handlerton::discovered_list
 };
 
 int ha_discover_table(THD *thd, TABLE_SHARE *share);
-int ha_discover_table_names(THD *thd, LEX_CSTRING *db, MY_DIR *dirp,
+int ha_discover_table_names(THD *thd, const LEX_CSTRING *db, MY_DIR *dirp,
                             Discovered_table_list *result, bool reusable);
 bool ha_table_exists(THD *thd, const LEX_CSTRING *db,
                      const LEX_CSTRING *table_name,

sql/lex_ident.h

@@ -87,9 +87,16 @@ class DBNameBuffer: public CharBuffer<SAFE_NAME_LEN + MY_CS_MBMAXLEN>
   {
     copy_casedn(&my_charset_utf8mb3_general_ci, db, casedn);
   }
+  Lex_ident_db to_lex_ident_db() const
+  {
+    const LEX_CSTRING tmp= to_lex_cstring();
+    if (Lex_ident_fs(tmp).check_db_name())
+      return Lex_ident_db();
+    return Lex_ident_db(tmp.str, tmp.length);
+  }
   Lex_ident_db to_lex_ident_db_with_error() const
   {
-    LEX_CSTRING tmp= to_lex_cstring();
+    const LEX_CSTRING tmp= to_lex_cstring();
     if (Lex_ident_fs(tmp).check_db_name_with_error())
       return Lex_ident_db();
     return Lex_ident_db(tmp.str, tmp.length);

sql/sql_show.cc

@@ -948,7 +948,8 @@ enum find_files_result {
 
 
 static find_files_result
-find_files(THD *thd, Dynamic_array<LEX_CSTRING*> *files, LEX_CSTRING *db,
+find_files(THD *thd, Dynamic_array<LEX_CSTRING*> *files,
+           const Lex_ident_db *db,
            const char *path, const LEX_CSTRING *wild)
 {
   MY_DIR *dirp;
@@ -4537,7 +4538,7 @@ int schema_tables_add(THD *thd, Dynamic_array<LEX_CSTRING*> *files,
 static int
 make_table_name_list(THD *thd, Dynamic_array<LEX_CSTRING*> *table_names,
                      LEX *lex, LOOKUP_FIELD_VALUES *lookup_field_vals,
-                     LEX_CSTRING *db_name)
+                     const LEX_CSTRING *db_name)
 {
   char path[FN_REFLEN + 1];
   build_table_filename(path, sizeof(path) - 1, db_name->str, "", "", 0);
@@ -4583,10 +4584,12 @@ make_table_name_list(THD *thd, Dynamic_array<LEX_CSTRING*> *table_names,
     return (schema_tables_add(thd, table_names,
                               lookup_field_vals->table_value.str));
 
-  if (check_db_name((LEX_STRING*)db_name))
+  DBNameBuffer dbbuf(*db_name, lower_case_table_names);
+  const Lex_ident_db dbnorm= dbbuf.to_lex_ident_db();
+  if (!dbnorm.str)
     return 0; // Impossible TABLE_SCHEMA name
 
-  find_files_result res= find_files(thd, table_names, db_name, path,
+  find_files_result res= find_files(thd, table_names, &dbnorm, path,
                                     &lookup_field_vals->table_value);
   if (res != FIND_FILES_OK)
   {

storage/maria/ha_s3.cc

@@ -827,7 +827,7 @@ static int s3_discover_table_existence(handlerton *hton, const char *db,
 */
 
 static int s3_discover_table_names(handlerton *hton __attribute__((unused)),
-                                   LEX_CSTRING *db,
+                                   const LEX_CSTRING *db,
                                    MY_DIR *dir __attribute__((unused)),
                                    handlerton::discovered_list *result)
 {

storage/perfschema/pfs_engine_table.cc

@@ -1960,7 +1960,7 @@ bool pfs_show_status(handlerton *hton, THD *thd,
 }
 
 int pfs_discover_table_names(handlerton *hton __attribute__((unused)),
-                             LEX_CSTRING *db,
+                             const LEX_CSTRING *db,
                              MY_DIR *dir __attribute__((unused)),
                              handlerton::discovered_list *result)
 {

storage/perfschema/pfs_engine_table.h

@@ -619,7 +619,7 @@ struct PFS_triple_index
 bool pfs_show_status(handlerton *hton, THD *thd,
                      stat_print_fn *print, enum ha_stat_type stat);
 
-int pfs_discover_table_names(handlerton *hton, LEX_CSTRING *db,
+int pfs_discover_table_names(handlerton *hton, const LEX_CSTRING *db,
                              MY_DIR *dir,
                              handlerton::discovered_list *result);