Make executor's SELECT INTO code save and restore original tuple receiver.

As previously coded, the QueryDesc's dest pointer was left dangling
(pointing at an already-freed receiver object) after ExecutorEnd.  It's a
bit astonishing that it took us this long to notice, and I'm not sure that
the known problem case with SQL functions is the only one.  Fix it by
saving and restoring the original receiver pointer, which seems the most
bulletproof way of ensuring any related bugs are also covered.

Per bug #6379 from Paul Ramsey.  Back-patch to 8.4 where the current
handling of SELECT INTO was introduced.

src/backend/executor/execMain.c

@@ -2445,6 +2445,7 @@ typedef struct
 {
 	DestReceiver pub;			/* publicly-known function pointers */
 	EState	   *estate;			/* EState we are working with */
+	DestReceiver *origdest;		/* QueryDesc's original receiver */
 	Relation	rel;			/* Relation to write to */
 	int			hi_options;		/* heap_insert performance options */
 	BulkInsertState bistate;	/* bulk insert state */
@@ -2651,12 +2652,14 @@ OpenIntoRel(QueryDesc *queryDesc)
 	/*
 	 * Now replace the query's DestReceiver with one for SELECT INTO
 	 */
-	queryDesc->dest = CreateDestReceiver(DestIntoRel);
-	myState = (DR_intorel *) queryDesc->dest;
+	myState = (DR_intorel *) CreateDestReceiver(DestIntoRel);
 	Assert(myState->pub.mydest == DestIntoRel);
 	myState->estate = estate;
+	myState->origdest = queryDesc->dest;
 	myState->rel = intoRelationDesc;
 
+	queryDesc->dest = (DestReceiver *) myState;
+
 	/*
 	 * We can skip WAL-logging the insertions, unless PITR or streaming
 	 * replication is in use. We can skip the FSM in any case.
@@ -2677,8 +2680,11 @@ CloseIntoRel(QueryDesc *queryDesc)
 {
 	DR_intorel *myState = (DR_intorel *) queryDesc->dest;
 
-	/* OpenIntoRel might never have gotten called */
-	if (myState && myState->pub.mydest == DestIntoRel && myState->rel)
+	/*
+	 * OpenIntoRel might never have gotten called, and we also want to guard
+	 * against double destruction.
+	 */
+	if (myState && myState->pub.mydest == DestIntoRel)
 	{
 		FreeBulkInsertState(myState->bistate);
 
@@ -2689,7 +2695,11 @@ CloseIntoRel(QueryDesc *queryDesc)
 		/* close rel, but keep lock until commit */
 		heap_close(myState->rel, NoLock);
 
-		myState->rel = NULL;
+		/* restore the receiver belonging to executor's caller */
+		queryDesc->dest = myState->origdest;
+
+		/* might as well invoke my destructor */
+		intorel_destroy((DestReceiver *) myState);
 	}
 }
 

src/test/regress/expected/select_into.out

@@ -50,3 +50,28 @@ DETAIL:  drop cascades to table selinto_schema.tmp1
 drop cascades to table selinto_schema.tmp2
 drop cascades to table selinto_schema.tmp3
 DROP USER selinto_user;
+--
+-- CREATE TABLE AS/SELECT INTO as last command in a SQL function
+-- have been known to cause problems
+--
+CREATE FUNCTION make_table() RETURNS VOID
+AS $$
+  CREATE TABLE created_table AS SELECT * FROM int8_tbl;
+$$ LANGUAGE SQL;
+SELECT make_table();
+ make_table 
+------------
+ 
+(1 row)
+
+SELECT * FROM created_table;
+        q1        |        q2         
+------------------+-------------------
+              123 |               456
+              123 |  4567890123456789
+ 4567890123456789 |               123
+ 4567890123456789 |  4567890123456789
+ 4567890123456789 | -4567890123456789
+(5 rows)
+
+DROP TABLE created_table;

src/test/regress/sql/select_into.sql

@@ -52,3 +52,18 @@ RESET SESSION AUTHORIZATION;
 
 DROP SCHEMA selinto_schema CASCADE;
 DROP USER selinto_user;
+
+--
+-- CREATE TABLE AS/SELECT INTO as last command in a SQL function
+-- have been known to cause problems
+--
+CREATE FUNCTION make_table() RETURNS VOID
+AS $$
+  CREATE TABLE created_table AS SELECT * FROM int8_tbl;
+$$ LANGUAGE SQL;
+
+SELECT make_table();
+
+SELECT * FROM created_table;
+
+DROP TABLE created_table;