Properly initialize SortSupport for ORDER BY rechecks in nodeIndexscan.c.

Fix still another bug in commit 35fcb1b3d: it failed to fully initialize
the SortSupport states it introduced to allow the executor to re-check
ORDER BY expressions containing distance operators.  That led to a null
pointer dereference if the sortsupport code tried to use ssup_cxt.  The
problem only manifests in narrow cases, explaining the lack of previous
field reports.  It requires a GiST-indexable distance operator that lacks
SortSupport and is on a pass-by-ref data type, which among core+contrib
seems to be only btree_gist's interval opclass; and it requires the scan
to be done as an IndexScan not an IndexOnlyScan, which explains how
btree_gist's regression test didn't catch it.  Per bug #14134 from
Jihyun Yu.

Peter Geoghegan

Report: <20160511154904.2603.43889@wrigleys.postgresql.org>

contrib/btree_gist/expected/interval.out

@@ -89,3 +89,21 @@ SELECT a, a <-> '199 days 21:21:23' FROM intervaltmp ORDER BY a <-> '199 days 21
  @ 220 days 19 hours 5 mins 42 secs  | @ 21 days -2 hours -15 mins -41 secs
 (3 rows)
 
+SET enable_indexonlyscan=off;
+EXPLAIN (COSTS OFF)
+SELECT a, a <-> '199 days 21:21:23' FROM intervaltmp ORDER BY a <-> '199 days 21:21:23' LIMIT 3;
+                                QUERY PLAN                                 
+---------------------------------------------------------------------------
+ Limit
+   ->  Index Scan using intervalidx on intervaltmp
+         Order By: (a <-> '@ 199 days 21 hours 21 mins 23 secs'::interval)
+(3 rows)
+
+SELECT a, a <-> '199 days 21:21:23' FROM intervaltmp ORDER BY a <-> '199 days 21:21:23' LIMIT 3;
+                  a                  |               ?column?               
+-------------------------------------+--------------------------------------
+ @ 199 days 21 hours 21 mins 23 secs | @ 0
+ @ 183 days 6 hours 52 mins 48 secs  | @ 16 days 14 hours 28 mins 35 secs
+ @ 220 days 19 hours 5 mins 42 secs  | @ 21 days -2 hours -15 mins -41 secs
+(3 rows)
+

contrib/btree_gist/sql/interval.sql

@@ -35,3 +35,9 @@ SELECT count(*) FROM intervaltmp WHERE a >  '199 days 21:21:23'::interval;
 EXPLAIN (COSTS OFF)
 SELECT a, a <-> '199 days 21:21:23' FROM intervaltmp ORDER BY a <-> '199 days 21:21:23' LIMIT 3;
 SELECT a, a <-> '199 days 21:21:23' FROM intervaltmp ORDER BY a <-> '199 days 21:21:23' LIMIT 3;
+
+SET enable_indexonlyscan=off;
+
+EXPLAIN (COSTS OFF)
+SELECT a, a <-> '199 days 21:21:23' FROM intervaltmp ORDER BY a <-> '199 days 21:21:23' LIMIT 3;
+SELECT a, a <-> '199 days 21:21:23' FROM intervaltmp ORDER BY a <-> '199 days 21:21:23' LIMIT 3;

src/backend/executor/nodeIndexscan.c

@@ -967,9 +967,20 @@ ExecInitIndexScan(IndexScan *node, EState *estate, int eflags)
 			Oid			orderbyop = lfirst_oid(lco);
 			Node	   *orderbyexpr = (Node *) lfirst(lcx);
 			Oid			orderbyType = exprType(orderbyexpr);
+			Oid			orderbyColl = exprCollation(orderbyexpr);
+			SortSupport orderbysort = &indexstate->iss_SortSupport[i];
+
+			/* Initialize sort support */
+			orderbysort->ssup_cxt = CurrentMemoryContext;
+			orderbysort->ssup_collation = orderbyColl;
+			/* See cmp_orderbyvals() comments on NULLS LAST */
+			orderbysort->ssup_nulls_first = false;
+			/* ssup_attno is unused here and elsewhere */
+			orderbysort->ssup_attno = 0;
+			/* No abbreviation */
+			orderbysort->abbreviate = false;
+			PrepareSortSupportFromOrderingOp(orderbyop, orderbysort);
 
-			PrepareSortSupportFromOrderingOp(orderbyop,
-											 &indexstate->iss_SortSupport[i]);
 			get_typlenbyval(orderbyType,
 							&indexstate->iss_OrderByTypLens[i],
 							&indexstate->iss_OrderByTypByVals[i]);