MDEV-5526 Assertion `proxied_user->host.length' fails on GRANT PROXY ON <role>

recognize the context better:
always treat the barename as a username in the username context

mysql-test/suite/roles/create_and_drop_role.result

@@ -38,5 +38,5 @@ create role '';
 ERROR OP000: Invalid role specification ``.
 create role r1;
 drop user r1;
-ERROR HY000: Operation DROP USER failed for 'r1'
+ERROR HY000: Operation DROP USER failed for 'r1'@'%'
 drop role r1;

mysql-test/suite/roles/grant_proxy-5526.result

+create role r1;
+create user user;
+grant proxy on r1 to user;
+show grants for user;
+Grants for user@%
+GRANT USAGE ON *.* TO 'user'@'%'
+GRANT PROXY ON 'r1'@'%' TO 'user'@'%'
+drop user user;
+drop role r1;

mysql-test/suite/roles/grant_proxy-5526.test

+#
+# MDEV-5526 Assertion `proxied_user->host.length' fails on GRANT PROXY ON <role>
+#
+create role r1;
+create user user;
+grant proxy on r1 to user;
+show grants for user;
+drop user user;
+drop role r1;
+

mysql-test/suite/roles/password.result

 create role r1;
 grant select on *.* to r1 identified by 'foobar';
-ERROR 28000: Can't find any matching row in the user table
+drop user r1;
 grant select on *.* to r1 identified by '';
-ERROR 28000: Can't find any matching row in the user table
+drop user r1;
 grant select on mysql.user to r1 identified by password '00000000000000000000000000000000000000000';
-ERROR 28000: Can't find any matching row in the user table
+drop user r1;
 grant select on *.* to r1 identified via plugin;
-ERROR 28000: Can't find any matching row in the user table
+ERROR HY000: Plugin 'plugin' is not loaded
 grant select on mysql.user to r1 identified via plugin using 'param';
-ERROR 28000: Can't find any matching row in the user table
+ERROR HY000: Plugin 'plugin' is not loaded
 grant select on *.* to r1 require subject 'foobar';
 ERROR 28000: Can't find any matching row in the user table
 grant select on mysql.user to r1 require issuer 'foobar';

mysql-test/suite/roles/password.test

@@ -12,16 +12,18 @@
 
 create role r1;
 
---error ER_PASSWORD_NO_MATCH
+# IDENTIFIED does not apply to roles, using it forces username context
 grant select on *.* to r1 identified by 'foobar';
---error ER_PASSWORD_NO_MATCH
+drop user r1;
 grant select on *.* to r1 identified by '';
---error ER_PASSWORD_NO_MATCH
+drop user r1;
 grant select on mysql.user to r1 identified by password '00000000000000000000000000000000000000000';
---error ER_PASSWORD_NO_MATCH
+drop user r1;
+--error ER_PLUGIN_IS_NOT_LOADED
 grant select on *.* to r1 identified via plugin;
---error ER_PASSWORD_NO_MATCH
+--error ER_PLUGIN_IS_NOT_LOADED
 grant select on mysql.user to r1 identified via plugin using 'param';
+
 --error ER_PASSWORD_NO_MATCH
 grant select on *.* to r1 require subject 'foobar';
 --error ER_PASSWORD_NO_MATCH

sql/sql_acl.cc

@@ -8351,7 +8351,7 @@ static int handle_roles_mappings_table(TABLE *table, bool drop,
       {
         role= safe_str(get_field(thd->mem_root, role_field));
 
-        if (strcmp(user_from->user.str, role))
+        if (!user_from->is_role() || strcmp(user_from->user.str, role))
           continue;
 
         error= 0;
@@ -8574,7 +8574,6 @@ static int handle_grant_struct(enum enum_acl_lists struct_no, bool drop,
   const char *UNINIT_VAR(user);
   const char *UNINIT_VAR(host);
   const char *UNINIT_VAR(role);
-  uint role_not_matched= 1;
   ACL_USER *acl_user= NULL;
   ACL_ROLE *acl_role= NULL;
   ACL_DB *acl_db= NULL;
@@ -8734,8 +8733,7 @@ static int handle_grant_struct(enum enum_acl_lists struct_no, bool drop,
 
     if (struct_no == ROLES_MAPPINGS_HASH)
     {
-      role_not_matched= strcmp(user_from->user.str, role);
-      if (role_not_matched &&
+      if (user_from->is_role() ? strcmp(user_from->user.str, role) :
           (strcmp(user_from->user.str, user) ||
            my_strcasecmp(system_charset_info, user_from->host.str, host)))
         continue;
@@ -8858,14 +8856,14 @@ static int handle_grant_struct(enum enum_acl_lists struct_no, bool drop,
           size_t old_key_length= role_grant_pair->hashkey.length;
           bool oom;
 
-          if (role_not_matched)
-            oom= role_grant_pair->init(&acl_memroot, user_to->user.str,
-                                       user_to->host.str,
-                                       role_grant_pair->r_uname, false);
-          else
+          if (user_to->is_role())
             oom= role_grant_pair->init(&acl_memroot, role_grant_pair->u_uname,
                                        role_grant_pair->u_hname,
                                        user_to->user.str, false);
+          else
+            oom= role_grant_pair->init(&acl_memroot, user_to->user.str,
+                                       user_to->host.str,
+                                       role_grant_pair->r_uname, false);
           if (oom)
             DBUG_RETURN(-1);
 
@@ -9349,20 +9347,20 @@ bool mysql_rename_user(THD *thd, List <LEX_USER> &list)
   while ((tmp_user_from= user_list++))
   {
     tmp_user_to= user_list++;
-    if (!(user_from= get_current_user(thd, tmp_user_from, false)) ||
-        user_from->is_role())
+    if (!(user_from= get_current_user(thd, tmp_user_from, false)))
     {
       append_user(&wrong_users, user_from);
       result= TRUE;
       continue;
     }
-    if (!(user_to= get_current_user(thd, tmp_user_to, false)) ||
-        user_to->is_role())
+    if (!(user_to= get_current_user(thd, tmp_user_to, false)))
     {
       append_user(&wrong_users, user_to);
       result= TRUE;
       continue;
     }
+    DBUG_ASSERT(!user_from->is_role());
+    DBUG_ASSERT(!user_to->is_role());
 
     /*
       Search all in-memory structures and grant tables

sql/sql_yacc.yy

@@ -1771,7 +1771,7 @@ bool my_yyoverflow(short **a, YYSTYPE **b, ulong *yystacksize);
 %type <symbol> keyword keyword_sp
 
 %type <lex_user> user grant_user grant_role user_or_role current_role
-                 admin_option_for_role
+                 admin_option_for_role user_maybe_role
 
 %type <charset>
         opt_collate
@@ -13916,7 +13916,7 @@ ident_or_text:
         | LEX_HOSTNAME { $$=$1;}
         ;
 
-user:
+user_maybe_role:
           ident_or_text
           {
             if (!($$=(LEX_USER*) thd->alloc(sizeof(st_lex_user))))
@@ -13974,7 +13974,15 @@ user:
           }
         ;
 
-user_or_role: user | current_role;
+user_or_role: user_maybe_role | current_role;
+
+user: user_maybe_role
+         {
+           if ($1->user.str != current_user.str && $1->host.str == 0)
+             $1->host= host_not_specified;
+           $$= $1;
+         }
+         ;
 
 /* Keyword that we allow for identifiers (except SP labels) */
 keyword: