Bug#15463: EXPLAIN SELECT..INTO hangs the client (QB, command line)

There were two distict bugs: parse error was returned for valid
statement and that error wasn't reported to the client.

The fix ensures that EXPLAIN SELECT..INTO is accepted by parser and any
other parse error will be reported to the client.

mysql-test/r/explain.result

@@ -53,3 +53,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE		ref	0,01	0	5	const	1	Using where; Using index
 drop table ;
 set names latin1;
+select 3 into @v1;
+explain select 3 into @v1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used

mysql-test/t/explain.test

@@ -43,3 +43,12 @@ drop table
 set names latin1;
 
 # End of 4.1 tests
+
+
+#
+# Bug#15463: EXPLAIN SELECT..INTO hangs the client (QB, command line)
+#
+select 3 into @v1;
+explain select 3 into @v1;
+
+# End of 5.0 tests.

sql/sql_parse.cc

@@ -5709,6 +5709,7 @@ void mysql_parse(THD *thd, char *inBuf, uint length)
     }
     else
     {
+      DBUG_ASSERT(thd->net.report_error);
       DBUG_PRINT("info",("Command aborted. Fatal_error: %d",
 			 thd->is_fatal_error));
       query_cache_abort(&thd->net);

sql/sql_yacc.yy

@@ -5795,7 +5795,11 @@ select_var_ident:
 	     if (lex->result) 
 	       ((select_dumpvar *)lex->result)->var_list.push_back( new my_var($2,0,0,(enum_field_types)0));
 	     else
-	       YYABORT;
+               /*
+                 The parser won't create select_result instance only
+	         if it's an EXPLAIN.
+               */
+               DBUG_ASSERT(lex->describe);
 	   }
            | ident_or_text
            {
@@ -5807,9 +5811,7 @@ select_var_ident:
 	       my_error(ER_SP_UNDECLARED_VAR, MYF(0), $1.str);
 	       YYABORT;
 	     }
-	     if (! lex->result)
-	       YYABORT;
-	     else
+	     if (lex->result)
              {
                my_var *var;
 	       ((select_dumpvar *)lex->result)->
@@ -5819,6 +5821,14 @@ select_var_ident:
 		 var->sp= lex->sphead;
 #endif
              }
+	     else
+	     {
+               /*
+                 The parser won't create select_result instance only
+	         if it's an EXPLAIN.
+               */
+               DBUG_ASSERT(lex->describe);
+	     }
 	   }
            ;