MDEV-36675 Optimizer hints parser catches irrelevant thd->is_error() set by multi-RENAME TABLE

Optimizer hints parser analyzes `thd->is_error()` flag to detect a fatal
error occured during hints processing. However, this criteria is not
reliable and considered a bad practice.
This commit replaces the criteria with the parser's own `is_fatal_error()`
flag which is related strictly to hints parsing and not something else

mysql-test/main/opt_hints.result

@@ -1985,5 +1985,21 @@ DROP TABLE t1;
 set optimizer_switch = DEFAULT;
 set join_cache_level = DEFAULT;
 #
-# End of 11.7 tests
+# MDEV-36675 Optimizer hints parser catches irrelevant `thd->is_error()`
+#              set by multi-RENAME TABLE
+#
+CREATE TABLE t1 (a INT);
+CREATE TRIGGER t1 AFTER INSERT ON t1 FOR EACH ROW INSERT INTO t1 VALUES (0);
+RENAME TABLE t1 TO t2, t3 TO t4;
+ERROR 42S02: Table 'test.t3' doesn't exist
+SHOW CREATE TRIGGER t1;
+Trigger	sql_mode	SQL Original Statement	character_set_client	collation_connection	Database Collation	Created
+t1		CREATE DEFINER=`root`@`localhost` TRIGGER t1 AFTER INSERT ON `t1` FOR EACH ROW INSERT INTO t1 VALUES (0)	utf8mb3	utf8mb3_uca1400_ai_ci	utf8mb4_uca1400_ai_ci	#
+RENAME TABLE t1 TO t2;
+SHOW CREATE TRIGGER t1;
+Trigger	sql_mode	SQL Original Statement	character_set_client	collation_connection	Database Collation	Created
+t1		CREATE DEFINER=`root`@`localhost` TRIGGER t1 AFTER INSERT ON `t2` FOR EACH ROW INSERT INTO t1 VALUES (0)	utf8mb3	utf8mb3_uca1400_ai_ci	utf8mb4_uca1400_ai_ci	#
+DROP TABLE t2;
+#
+# End of 12.0 tests
 #

mysql-test/main/opt_hints.test

@@ -1021,6 +1021,24 @@ SELECT
 DROP TABLE t1;
 set optimizer_switch = DEFAULT;
 set join_cache_level = DEFAULT;
+
 --echo #
---echo # End of 11.7 tests
+--echo # MDEV-36675 Optimizer hints parser catches irrelevant `thd->is_error()`
+--echo #              set by multi-RENAME TABLE
+--echo #
+CREATE TABLE t1 (a INT);
+CREATE TRIGGER t1 AFTER INSERT ON t1 FOR EACH ROW INSERT INTO t1 VALUES (0);
+--error ER_NO_SUCH_TABLE
+RENAME TABLE t1 TO t2, t3 TO t4;
+
+--replace_column 7 #
+SHOW CREATE TRIGGER t1;
+RENAME TABLE t1 TO t2;
+
+--replace_column 7 #
+SHOW CREATE TRIGGER t1;
+DROP TABLE t2;
+
+--echo #
+--echo # End of 12.0 tests
 --echo #

sql/sql_lex.cc

@@ -12932,22 +12932,22 @@ bool SELECT_LEX_UNIT::is_derived_eliminated() const
 /*
   Parse optimizer hints and return as Hint_list allocated on thd->mem_root.
 
-  The caller should check both return value and thd->is_error()
+  The caller should check both parts of the return value
   to know what happened, as follows:
 
-  Return value   thd->is_error()  Meaning
+  Retval.first   Retval.second    Meaning
   ------------   ---------------  -------
-  rc != nullptr  false            the hints were parsed without errors
-  rc != nullptr  true             not possible
-  rc == nullptr  false            no hints, empty hints, hint parse error
-  rc == nullptr  true             fatal error, such as EOM
+  false          != nullptr       the hints were parsed without errors
+  true           != nullptr       impossible combination
+  false          == nullptr       no hints, empty hints, hint parse error
+  true           == nullptr       fatal error, such as EOM
 */
-Optimizer_hint_parser_output *
+std::pair<bool, Optimizer_hint_parser_output *>
 LEX::parse_optimizer_hints(const Lex_comment_st &hints_str)
 {
   DBUG_ASSERT(!hints_str.str || hints_str.length >= 5);
   if (!hints_str.str)
-    return nullptr; // There were no a hint comment
+    return {false, nullptr}; // There were no a hint comment
 
   //  Instantiate the query hint parser.
   //  Remove the leading '/*+' and trailing '*/'
@@ -12965,17 +12965,17 @@ LEX::parse_optimizer_hints(const Lex_comment_st &hints_str)
       The SQL error should be in DA already.
     */
     DBUG_ASSERT(thd->is_error());
-    return nullptr; // Continue, the caller will test thd->is_error()
+    return {true, nullptr}; // Set the flag of fatal error
   }
 
   if (!hints) // Hint parsing failed with a syntax error
   {
     p.push_warning_syntax_error(thd, hints_str.lineno);
-    return nullptr; // Continue and ignore hints.
+    return {false, nullptr}; // Continue and ignore hints.
   }
 
   // Hints were not empty and were parsed without errors
-  return new (thd->mem_root) Optimizer_hint_parser_output(std::move(hints));
+  return {false, new (thd->mem_root) Optimizer_hint_parser_output(std::move(hints))};
 }
 
 

sql/sql_lex.h

@@ -5001,7 +5001,7 @@ public:
     return nullptr;
   }
 
-  Optimizer_hint_parser_output *
+  std::pair<bool, Optimizer_hint_parser_output *>
     parse_optimizer_hints(const Lex_comment_st &hint);
 };
 

sql/sql_yacc.yy

@@ -8971,7 +8971,9 @@ opt_optimizer_hint:
           opt_hint_comment
           {
             YYLIP->hint_comment= false;
-            if (!($$= Lex->parse_optimizer_hints($2)) && thd->is_error())
+            std::pair<bool, Optimizer_hint_parser_output *> parse_res=
+              Lex->parse_optimizer_hints($2);
+            if (!($$= parse_res.second) && parse_res.first)
               MYSQL_YYABORT;
           }
         ;