Make viewquery a copy in rewriteTargetView()

Rather than expect the Query returned by get_view_query() to be
read-only and then copy bits and pieces of it out, simply copy the
entire structure when we get it.  This addresses an issue where
AcquireRewriteLocks, which is called by acquireLocksOnSubLinks(),
scribbles on the parsetree passed in, which was actually an entry
in relcache, leading to segfaults with certain view definitions.
This also future-proofs us a bit for anyone adding more code to this
path.

The acquireLocksOnSubLinks() was added in commit c3e0ddd4.

Back-patch to 9.3 as that commit was.

src/backend/rewrite/rewriteHandler.c

@@ -2033,6 +2033,9 @@ fireRules(Query *parsetree,
  *
  * Caller should have verified that the relation is a view, and therefore
  * we should find an ON SELECT action.
+ *
+ * Note that the pointer returned is into the relcache and therefore must
+ * be treated as read-only to the caller and not modified or scribbled on.
  */
 Query *
 get_view_query(Relation view)
@@ -2620,9 +2623,16 @@ rewriteTargetView(Query *parsetree, Relation view)
 	List	   *view_targetlist;
 	ListCell   *lc;
 
-	/* The view must be updatable, else fail */
-	viewquery = get_view_query(view);
+	/*
+	 * Get the Query from the view's ON SELECT rule.  We're going to munge the
+	 * Query to change the view's base relation into the target relation,
+	 * along with various other changes along the way, so we need to make a
+	 * copy of it (get_view_query() returns a pointer into the relcache, so we
+	 * have to treat it as read-only).
+	 */
+	viewquery = copyObject(get_view_query(view));
 
+	/* The view must be updatable, else fail */
 	auto_update_detail =
 		view_query_is_auto_updatable(viewquery,
 									 parsetree->commandType != CMD_DELETE);
@@ -2786,7 +2796,7 @@ rewriteTargetView(Query *parsetree, Relation view)
 	 * outer query.  Perhaps someday we should refactor things enough so that
 	 * we can share code with the planner.)
 	 */
-	new_rte = (RangeTblEntry *) copyObject(base_rte);
+	new_rte = (RangeTblEntry *) base_rte;
 	parsetree->rtable = lappend(parsetree->rtable, new_rte);
 	new_rt_index = list_length(parsetree->rtable);
 
@@ -2798,14 +2808,14 @@ rewriteTargetView(Query *parsetree, Relation view)
 		new_rte->inh = false;
 
 	/*
-	 * Make a copy of the view's targetlist, adjusting its Vars to reference
-	 * the new target RTE, ie make their varnos be new_rt_index instead of
-	 * base_rt_index.  There can be no Vars for other rels in the tlist, so
-	 * this is sufficient to pull up the tlist expressions for use in the
-	 * outer query.  The tlist will provide the replacement expressions used
-	 * by ReplaceVarsFromTargetList below.
+	 * Adjust the view's targetlist Vars to reference the new target RTE, ie
+	 * make their varnos be new_rt_index instead of base_rt_index.  There can
+	 * be no Vars for other rels in the tlist, so this is sufficient to pull
+	 * up the tlist expressions for use in the outer query.  The tlist will
+	 * provide the replacement expressions used by ReplaceVarsFromTargetList
+	 * below.
 	 */
-	view_targetlist = copyObject(viewquery->targetList);
+	view_targetlist = viewquery->targetList;
 
 	ChangeVarNodes((Node *) view_targetlist,
 				   base_rt_index,
@@ -2956,7 +2966,7 @@ rewriteTargetView(Query *parsetree, Relation view)
 	if (parsetree->commandType != CMD_INSERT &&
 		viewquery->jointree->quals != NULL)
 	{
-		Node	   *viewqual = (Node *) copyObject(viewquery->jointree->quals);
+		Node	   *viewqual = (Node *) viewquery->jointree->quals;
 
 		ChangeVarNodes(viewqual, base_rt_index, new_rt_index, 0);
 
@@ -3035,7 +3045,7 @@ rewriteTargetView(Query *parsetree, Relation view)
 
 			if (viewquery->jointree->quals != NULL)
 			{
-				wco->qual = (Node *) copyObject(viewquery->jointree->quals);
+				wco->qual = (Node *) viewquery->jointree->quals;
 				ChangeVarNodes(wco->qual, base_rt_index, new_rt_index, 0);
 
 				/*

src/test/regress/expected/updatable_views.out

@@ -2353,3 +2353,70 @@ DROP TABLE t1, t11, t12, t111 CASCADE;
 NOTICE:  drop cascades to view v1
 DROP FUNCTION snoop(anyelement);
 DROP FUNCTION leakproof(anyelement);
+CREATE TABLE tx1 (a integer);
+CREATE TABLE tx2 (b integer);
+CREATE TABLE tx3 (c integer);
+CREATE VIEW vx1 AS SELECT a FROM tx1 WHERE EXISTS(SELECT 1 FROM tx2 JOIN tx3 ON b=c);
+INSERT INTO vx1 values (1);
+SELECT * FROM tx1;
+ a 
+---
+ 1
+(1 row)
+
+SELECT * FROM vx1;
+ a 
+---
+(0 rows)
+
+DROP VIEW vx1;
+DROP TABLE tx1;
+DROP TABLE tx2;
+DROP TABLE tx3;
+CREATE TABLE tx1 (a integer);
+CREATE TABLE tx2 (b integer);
+CREATE TABLE tx3 (c integer);
+CREATE VIEW vx1 AS SELECT a FROM tx1 WHERE EXISTS(SELECT 1 FROM tx2 JOIN tx3 ON b=c);
+INSERT INTO vx1 VALUES (1);
+INSERT INTO vx1 VALUES (1);
+SELECT * FROM tx1;
+ a 
+---
+ 1
+ 1
+(2 rows)
+
+SELECT * FROM vx1;
+ a 
+---
+(0 rows)
+
+DROP VIEW vx1;
+DROP TABLE tx1;
+DROP TABLE tx2;
+DROP TABLE tx3;
+CREATE TABLE tx1 (a integer, b integer);
+CREATE TABLE tx2 (b integer, c integer);
+CREATE TABLE tx3 (c integer, d integer);
+ALTER TABLE tx1 DROP COLUMN b;
+ALTER TABLE tx2 DROP COLUMN c;
+ALTER TABLE tx3 DROP COLUMN d;
+CREATE VIEW vx1 AS SELECT a FROM tx1 WHERE EXISTS(SELECT 1 FROM tx2 JOIN tx3 ON b=c);
+INSERT INTO vx1 VALUES (1);
+INSERT INTO vx1 VALUES (1);
+SELECT * FROM tx1;
+ a 
+---
+ 1
+ 1
+(2 rows)
+
+SELECT * FROM vx1;
+ a 
+---
+(0 rows)
+
+DROP VIEW vx1;
+DROP TABLE tx1;
+DROP TABLE tx2;
+DROP TABLE tx3;

src/test/regress/sql/updatable_views.sql

@@ -1020,3 +1020,47 @@ TABLE t1; -- verify all a<=5 are intact
 DROP TABLE t1, t11, t12, t111 CASCADE;
 DROP FUNCTION snoop(anyelement);
 DROP FUNCTION leakproof(anyelement);
+
+CREATE TABLE tx1 (a integer);
+CREATE TABLE tx2 (b integer);
+CREATE TABLE tx3 (c integer);
+CREATE VIEW vx1 AS SELECT a FROM tx1 WHERE EXISTS(SELECT 1 FROM tx2 JOIN tx3 ON b=c);
+INSERT INTO vx1 values (1);
+SELECT * FROM tx1;
+SELECT * FROM vx1;
+
+DROP VIEW vx1;
+DROP TABLE tx1;
+DROP TABLE tx2;
+DROP TABLE tx3;
+
+CREATE TABLE tx1 (a integer);
+CREATE TABLE tx2 (b integer);
+CREATE TABLE tx3 (c integer);
+CREATE VIEW vx1 AS SELECT a FROM tx1 WHERE EXISTS(SELECT 1 FROM tx2 JOIN tx3 ON b=c);
+INSERT INTO vx1 VALUES (1);
+INSERT INTO vx1 VALUES (1);
+SELECT * FROM tx1;
+SELECT * FROM vx1;
+
+DROP VIEW vx1;
+DROP TABLE tx1;
+DROP TABLE tx2;
+DROP TABLE tx3;
+
+CREATE TABLE tx1 (a integer, b integer);
+CREATE TABLE tx2 (b integer, c integer);
+CREATE TABLE tx3 (c integer, d integer);
+ALTER TABLE tx1 DROP COLUMN b;
+ALTER TABLE tx2 DROP COLUMN c;
+ALTER TABLE tx3 DROP COLUMN d;
+CREATE VIEW vx1 AS SELECT a FROM tx1 WHERE EXISTS(SELECT 1 FROM tx2 JOIN tx3 ON b=c);
+INSERT INTO vx1 VALUES (1);
+INSERT INTO vx1 VALUES (1);
+SELECT * FROM tx1;
+SELECT * FROM vx1;
+
+DROP VIEW vx1;
+DROP TABLE tx1;
+DROP TABLE tx2;
+DROP TABLE tx3;