Done!

please update the JIRA status after the trunk merge

the set_var grammar is in separate file and we cannot use the existing rules defined for "variable". So duplicated the rules in set_var grammar file. Still we get the below mentioned errors. After checking with Yura, we concluded that it is not straightforward to implement this. The parser for set_var is limited and not even YYTHD is available with SET_VAR grammar.

Conclusion: We take this up as separate task after the initial work is pushed

Patch that was tried for enabling SET_VAR(var_name=@@global.var_name)

diff --git a/sql/sql_hints.yy b/sql/sql_hints.yy
index df80fddacef..2d119d0f547 100644
— a/sql/sql_hints.yy
+++ b/sql/sql_hints.yy
@@ -89,6 +89,12 @@ static bool parse_int(longlong *to, const char *from, size_t from_length)
 %token INDEX_MERGE_HINT
 %token NO_INDEX_MERGE_HINT
 %token SET_VAR_HINT
+%token HINT_IDENT
+%token HINT_IDENT_QUOTED
+%token HINT_TEXT_STRING
+%token<keyword> HINT_GLOBAL_SYM
+%token<keyword> HINT_LOCAL_SYM
+%token<keyword> HINT_SESSION_SYM
 
 /* Other tokens */
 
@@ -150,11 +156,26 @@ static bool parse_int(longlong *to, const char *from, size_t from_length)
   set_var_num_item
   set_var_string_item
   set_var_arg
+  variable
+  variable_aux
 
 %type <ulong_num>
   semijoin_strategy semijoin_strategies
   subquery_strategy
 
+%type <lex_str>
+  HINT_IDENT
+  HINT_IDENT_QUOTED
+  hint_ident_or_text
+  hint_TEXT_STRING_sys
+  HINT_TEXT_STRING
+  hint_opt_component
+  hint_IDENT_sys
+  hint_ident
+
+%type <var_type>
+  hint_opt_var_ident_type
+
 %%
 
 
@@ -604,8 +625,88 @@ set_var_string_item:
           if ($$ == NULL)
             YYABORT; // OOM
         }
+
+variable:
+          '@' variable_aux { $$= $2; }
+        ;
+
+variable_aux:
+        '@' hint_opt_var_ident_type hint_ident_or_text hint_opt_component
+          {
+            $$= NEW_PTN PTI_variable_aux_3d(@$, $2, $3, @3, $4);
+          }
+        ;
+
+hint_opt_var_ident_type:
+          /* empty */     { $$=OPT_DEFAULT; }
+        | HINT_GLOBAL_SYM '.'  { $$=OPT_GLOBAL; }
+        | HINT_LOCAL_SYM '.'   { $$=OPT_SESSION; }
+        | HINT_SESSION_SYM '.' { $$=OPT_SESSION; }
+        ;
+
+hint_opt_component:
+          /* empty */    { $$= null_lex_str; }
+        | '.' hint_ident      { $$= $2; }
+        ;
+
+hint_ident_or_text:
+          hint_ident           { $$=$1;}
+        | hint_TEXT_STRING_sys { $$=$1;}
+        ;
+
+hint_ident:
+          hint_IDENT_sys    { $$=$1; }
+        ;
+
+hint_IDENT_sys:
+          HINT_IDENT { $$= $1; }
+        | HINT_IDENT_QUOTED
+          {
+            THD *thd= YYTHD;
+
+            if (thd->charset_is_system_charset)
+            {
+              const CHARSET_INFO *cs= system_charset_info;
+              int dummy_error;
+              size_t wlen= cs->cset->well_formed_len(cs, $1.str,
                                                     $1.str$1.length,
+                                                     $1.length, &dummy_error);
+              if (wlen < $1.length)
+              {
+                ErrConvString err($1.str, $1.length, &my_charset_bin);
+                my_error(ER_INVALID_CHARACTER_STRING, MYF(0),
+                         cs->csname, err.ptr());
+                MYSQL_YYABORT;
+              }
+              $$= $1;
+            }
+            else
+            {
+              if (thd->convert_string(&$$, system_charset_info,
+                                  $1.str, $1.length, thd->charset()))
+                MYSQL_YYABORT;
+            }
+          }
+        ;
+
+hint_TEXT_STRING_sys:
+          HINT_TEXT_STRING
+          {
+            THD *thd= YYTHD;
+
+            if (thd->charset_is_system_charset)
+              $$= $1;
+            else
+            {
+              if (thd->convert_string(&$$, system_charset_info,
+                                  $1.str, $1.length, thd->charset()))
+                MYSQL_YYABORT;
+            }
+          }
+        ;
 
 set_var_arg:
     set_var_string_item
     | set_var_num_item
+    | variable
     ;

===========

Errors seen:

/home/satya/WORK/mysql-8.0.11-set-statement/bld/sql/sql_hints.yy.cc: In function ‘int HINT_PARSER_parse(THD*, Hint_scanner*, PT_hint_list**)’:
/home/satya/WORK/mysql-8.0.11-set-statement/bld/sql/sql_hints.yy.cc:1481:48: error: cannot convert ‘YYLTYPE*’ to ‘Hint_scanner*’ for argument ‘2’ to ‘int HINT_PARSER_lex(YYSTYPE*, Hint_scanner*)’
      yychar = yylex (&yylval, &yylloc, scanner);
                                               ^
/home/satya/WORK/mysql-8.0.11-set-statement/sql/sql_hints.yy:636:35: error: expected type-specifier before ‘PTI_variable_aux_3d’
            $$= NEW_PTN PTI_variable_aux_3d(@$, $2, $3, @3, $4);
                                  ^~~~~~~~~~~~~~~~~~~
/home/satya/WORK/mysql-8.0.11-set-statement/sql/sql_hints.yy:665:23: error: ‘YYTHD’ was not declared in this scope
            THD *thd= YYTHD;

1) CALL /*+ SET_VAR(sort_buffer_size=10000) stored_proce_name() is working now! So we now have equivalent functionality as SET STATEMENT FOR.

What I found is same thd is used for for multiple mysql_execute_command() and lex and some stuff is reset after each statement.

Now onto make this work: SET_VAR(sort_buffer_size=default) AND SET_VAR(sort_buffer_size=@@global.sort_buffer_size)

1) it is not wrong syntax but the SET_VAR hint is ignored. I will check more on SET_VAR architecture. AFAIK, each mysql_execute_command() will read hint value and restore at the end of execution.  So from stored procedures, each statemnt would be one mysql_execute_command.

May be it will be possible to have hints with the CALL statement. Will need some more time to understand feasibility

2) I guess it is not about a setting that will make CREATE VIEW fail. A invalid SET_VAR always creates warning (never makes statement fail). Like I said above, it may be about how the parsed value is stored, applied and restored.

3) Right, I will check on how to make this work. It seems useful.

Also working on extending ALTER to take hints (specially for innodb_tmpdir).