More fixes for lossy-GiST-distance-functions patch.

Paul Ramsey reported that commit 35fcb1b3d038a501f3f4c87c05630095abaaadab
induced a core dump on commuted ORDER BY expressions, because it was
assuming that the indexorderby expression could be found verbatim in the
relevant equivalence class, but it wasn't there.  We really don't need
anything that complicated anyway; for the data types likely to be used for
index ORDER BY operators in the foreseeable future, the exprType() of the
ORDER BY expression will serve fine.  (The case where we'd have to work
harder is where the ORDER BY expression's result is only binary-compatible
with the declared input type of the ordering operator; long before worrying
about that, one would need to get rid of GiST's hard-wired assumption that
said datatype is float8.)

Aside from fixing that crash and adding a regression test for the case,
I did some desultory code review:

nodeIndexscan.c was likewise overthinking how hard it ought to work to
identify the datatype of the ORDER BY expressions.

Add comments explaining how come nodeIndexscan.c can get away with
simplifying assumptions about NULLS LAST ordering and no backward scan.

Revert no-longer-needed changes of find_ec_member_for_tle(); while the
new definition was no worse than the old, it wasn't better either, and
it might cause back-patching pain.

Revert entirely bogus additions to genam.h.

1 files changed, 33 insertions, 24 deletions

diff --git a/src/backend/executor/nodeIndexscan.c b/src/backend/executor/nodeIndexscan.c
index 96d34beaf43..d79c1aa8ca9 100644
--- a/src/backend/executor/nodeIndexscan.c
+++ b/src/backend/executor/nodeIndexscan.c
@@ -30,6 +30,7 @@
 #include "executor/execdebug.h"
 #include "executor/nodeIndexscan.h"
 #include "lib/pairingheap.h"
+#include "nodes/nodeFuncs.h"
 #include "optimizer/clauses.h"
 #include "utils/array.h"
 #include "utils/datum.h"
@@ -159,9 +160,18 @@ IndexNextWithReorder(IndexScanState *node)
 	bool	   *lastfetched_nulls;
 	int			cmp;
 
-	/* only forward scan is supported with reordering. */
+	/*
+	 * Only forward scan is supported with reordering.  Note: we can get away
+	 * with just Asserting here because the system will not try to run the
+	 * plan backwards if ExecSupportsBackwardScan() says it won't work.
+	 * Currently, that is guaranteed because no index AMs support both
+	 * amcanorderbyop and amcanbackward; if any ever do,
+	 * ExecSupportsBackwardScan() will need to consider indexorderbys
+	 * explicitly.
+	 */
 	Assert(!ScanDirectionIsBackward(((IndexScan *) node->ss.ps.plan)->indexorderdir));
 	Assert(ScanDirectionIsForward(node->ss.ps.state->es_direction));
+
 	scandesc = node->iss_ScanDesc;
 	econtext = node->ss.ps.ps_ExprContext;
 	slot = node->ss.ss_ScanTupleSlot;
@@ -370,7 +380,11 @@ cmp_orderbyvals(const Datum *adist, const bool *anulls,
 	{
 		SortSupport ssup = &node->iss_SortSupport[i];
 
-		/* Handle nulls.  We only support NULLS LAST. */
+		/*
+		 * Handle nulls.  We only need to support NULLS LAST ordering, because
+		 * match_pathkeys_to_index() doesn't consider indexorderby
+		 * implementation otherwise.
+		 */
 		if (anulls[i] && !bnulls[i])
 			return 1;
 		else if (!anulls[i] && bnulls[i])
@@ -388,7 +402,7 @@ cmp_orderbyvals(const Datum *adist, const bool *anulls,
 
 /*
  * Pairing heap provides getting topmost (greatest) element while KNN provides
- * ascending sort.  That's why we inverse the sort order.
+ * ascending sort.  That's why we invert the sort order.
  */
 static int
 reorderqueue_cmp(const pairingheap_node *a, const pairingheap_node *b,
@@ -917,35 +931,30 @@ ExecInitIndexScan(IndexScan *node, EState *estate, int eflags)
 	{
 		int			numOrderByKeys = indexstate->iss_NumOrderByKeys;
 		int			i;
-		ListCell   *lc;
+		ListCell   *lco;
+		ListCell   *lcx;
 
 		/*
-		 * Prepare sort support, and look up the distance type for each ORDER
-		 * BY expression.
+		 * Prepare sort support, and look up the data type for each ORDER BY
+		 * expression.
 		 */
 		Assert(numOrderByKeys == list_length(node->indexorderbyops));
-		indexstate->iss_SortSupport =
+		Assert(numOrderByKeys == list_length(node->indexorderbyorig));
+		indexstate->iss_SortSupport = (SortSupportData *)
 			palloc0(numOrderByKeys * sizeof(SortSupportData));
-		indexstate->iss_OrderByTypByVals =
+		indexstate->iss_OrderByTypByVals = (bool *)
 			palloc(numOrderByKeys * sizeof(bool));
-		indexstate->iss_OrderByTypLens =
+		indexstate->iss_OrderByTypLens = (int16 *)
 			palloc(numOrderByKeys * sizeof(int16));
 		i = 0;
-		foreach(lc, node->indexorderbyops)
+		forboth(lco, node->indexorderbyops, lcx, node->indexorderbyorig)
 		{
-			Oid orderbyop = lfirst_oid(lc);
-			Oid			orderbyType;
-			Oid			opfamily;
-			int16		strategy;
+			Oid			orderbyop = lfirst_oid(lco);
+			Node	   *orderbyexpr = (Node *) lfirst(lcx);
+			Oid			orderbyType = exprType(orderbyexpr);
 
 			PrepareSortSupportFromOrderingOp(orderbyop,
 											 &indexstate->iss_SortSupport[i]);
-
-			if (!get_ordering_op_properties(orderbyop,
-										 &opfamily, &orderbyType, &strategy))
-				elog(ERROR, "operator %u is not a valid ordering operator",
-					 orderbyop);
-
 			get_typlenbyval(orderbyType,
 							&indexstate->iss_OrderByTypLens[i],
 							&indexstate->iss_OrderByTypByVals[i]);
@@ -953,10 +962,10 @@ ExecInitIndexScan(IndexScan *node, EState *estate, int eflags)
 		}
 
 		/* allocate arrays to hold the re-calculated distances */
-		indexstate->iss_OrderByValues =
-			palloc(indexstate->iss_NumOrderByKeys * sizeof(Datum));
-		indexstate->iss_OrderByNulls =
-			palloc(indexstate->iss_NumOrderByKeys * sizeof(bool));
+		indexstate->iss_OrderByValues = (Datum *)
+			palloc(numOrderByKeys * sizeof(Datum));
+		indexstate->iss_OrderByNulls = (bool *)
+			palloc(numOrderByKeys * sizeof(bool));
 
 		/* and initialize the reorder queue */
 		indexstate->iss_ReorderQueue = pairingheap_allocate(reorderqueue_cmp,