Refactor ON CONFLICT index inference parse tree representation.

Defer lookup of opfamily and input type of a of a user specified opclass
until the optimizer selects among available unique indexes; and store
the opclass in the parse analyzed tree instead.  The primary reason for
doing this is that for rule deparsing it's easier to use the opclass
than the previous representation.

While at it also rename a variable in the inference code to better fit
it's purpose.

This is separate from the actual fixes for deparsing to make review
easier.

contrib/pg_stat_statements/pg_stat_statements.c

@@ -2645,8 +2645,7 @@ JumbleExpr(pgssJumbleState *jstate, Node *node)
 				InferenceElem *ie = (InferenceElem *) node;
 
 				APP_JUMB(ie->infercollid);
-				APP_JUMB(ie->inferopfamily);
-				APP_JUMB(ie->inferopcinputtype);
+				APP_JUMB(ie->inferopclass);
 				JumbleExpr(jstate, ie->expr);
 			}
 			break;

src/backend/nodes/copyfuncs.c

@@ -1839,8 +1839,7 @@ _copyInferenceElem(const InferenceElem *from)
 
 	COPY_NODE_FIELD(expr);
 	COPY_SCALAR_FIELD(infercollid);
-	COPY_SCALAR_FIELD(inferopfamily);
-	COPY_SCALAR_FIELD(inferopcinputtype);
+	COPY_SCALAR_FIELD(inferopclass);
 
 	return newnode;
 }

src/backend/nodes/equalfuncs.c

@@ -702,8 +702,7 @@ _equalInferenceElem(const InferenceElem *a, const InferenceElem *b)
 {
 	COMPARE_NODE_FIELD(expr);
 	COMPARE_SCALAR_FIELD(infercollid);
-	COMPARE_SCALAR_FIELD(inferopfamily);
-	COMPARE_SCALAR_FIELD(inferopcinputtype);
+	COMPARE_SCALAR_FIELD(inferopclass);
 
 	return true;
 }

src/backend/nodes/outfuncs.c

@@ -1474,8 +1474,7 @@ _outInferenceElem(StringInfo str, const InferenceElem *node)
 
 	WRITE_NODE_FIELD(expr);
 	WRITE_OID_FIELD(infercollid);
-	WRITE_OID_FIELD(inferopfamily);
-	WRITE_OID_FIELD(inferopcinputtype);
+	WRITE_OID_FIELD(inferopclass);
 }
 
 static void

src/backend/nodes/readfuncs.c

@@ -1214,8 +1214,7 @@ _readInferenceElem(void)
 
 	READ_NODE_FIELD(expr);
 	READ_OID_FIELD(infercollid);
-	READ_OID_FIELD(inferopfamily);
-	READ_OID_FIELD(inferopcinputtype);
+	READ_OID_FIELD(inferopclass);
 
 	READ_DONE();
 }

src/backend/optimizer/util/plancat.c

@@ -438,8 +438,8 @@ infer_arbiter_indexes(PlannerInfo *root)
 	Bitmapset  *inferAttrs = NULL;
 	List	   *inferElems = NIL;
 
-	/* Result */
-	List	   *candidates = NIL;
+	/* Results */
+	List	   *results = NIL;
 
 	/*
 	 * Quickly return NIL for ON CONFLICT DO NOTHING without an inference
@@ -565,11 +565,11 @@ infer_arbiter_indexes(PlannerInfo *root)
 						(errcode(ERRCODE_WRONG_OBJECT_TYPE),
 						 errmsg("ON CONFLICT DO UPDATE not supported with exclusion constraints")));
 
-			candidates = lappend_oid(candidates, idxForm->indexrelid);
+			results = lappend_oid(results, idxForm->indexrelid);
 			list_free(indexList);
 			index_close(idxRel, NoLock);
 			heap_close(relation, NoLock);
-			return candidates;
+			return results;
 		}
 		else if (indexOidFromConstraint != InvalidOid)
 		{
@@ -633,7 +633,7 @@ infer_arbiter_indexes(PlannerInfo *root)
 			 * index definition.
 			 */
 			if (elem->infercollid != InvalidOid ||
-				elem->inferopfamily != InvalidOid ||
+				elem->inferopclass != InvalidOid ||
 				list_member(idxExprs, elem->expr))
 				continue;
 
@@ -660,20 +660,20 @@ infer_arbiter_indexes(PlannerInfo *root)
 		if (!predicate_implied_by(predExprs, whereExplicit))
 			goto next;
 
-		candidates = lappend_oid(candidates, idxForm->indexrelid);
+		results = lappend_oid(results, idxForm->indexrelid);
 next:
 		index_close(idxRel, NoLock);
 	}
 
 	list_free(indexList);
 	heap_close(relation, NoLock);
 
-	if (candidates == NIL)
+	if (results == NIL)
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
 				 errmsg("there is no unique or exclusion constraint matching the ON CONFLICT specification")));
 
-	return candidates;
+	return results;
 }
 
 /*
@@ -709,23 +709,33 @@ infer_collation_opclass_match(InferenceElem *elem, Relation idxRel,
 							  Bitmapset *inferAttrs, List *idxExprs)
 {
 	AttrNumber	natt;
+	Oid			inferopfamily = InvalidOid;		/* OID of att opfamily */
+	Oid			inferopcinputtype = InvalidOid;		/* OID of att opfamily */
 
 	/*
 	 * If inference specification element lacks collation/opclass, then no
 	 * need to check for exact match.
 	 */
-	if (elem->infercollid == InvalidOid && elem->inferopfamily == InvalidOid)
+	if (elem->infercollid == InvalidOid && elem->inferopclass == InvalidOid)
 		return true;
 
+	/*
+	 * Lookup opfamily and input type, for matching indexes
+	 */
+	if (elem->inferopclass)
+	{
+		inferopfamily = get_opclass_family(elem->inferopclass);
+		inferopcinputtype = get_opclass_input_type(elem->inferopclass);
+	}
+
 	for (natt = 1; natt <= idxRel->rd_att->natts; natt++)
 	{
 		Oid		opfamily = idxRel->rd_opfamily[natt - 1];
 		Oid		opcinputtype = idxRel->rd_opcintype[natt - 1];
 		Oid		collation = idxRel->rd_indcollation[natt - 1];
 
-		if (elem->inferopfamily != InvalidOid &&
-			(elem->inferopfamily != opfamily ||
-			 elem->inferopcinputtype != opcinputtype))
+		if (elem->inferopclass != InvalidOid &&
+			(inferopfamily != opfamily || inferopcinputtype != opcinputtype))
 		{
 			/* Attribute needed to match opclass, but didn't */
 			continue;

src/backend/parser/parse_clause.c

@@ -2730,18 +2730,10 @@ resolve_unique_index_expr(ParseState *pstate, InferClause *infer,
 												  exprLocation(pInfer->expr));
 
 		if (!ielem->opclass)
-		{
-			pInfer->inferopfamily = InvalidOid;
-			pInfer->inferopcinputtype = InvalidOid;
-		}
+			pInfer->inferopclass = InvalidOid;
 		else
-		{
-			Oid		opclass = get_opclass_oid(BTREE_AM_OID, ielem->opclass,
-											  false);
-
-			pInfer->inferopfamily = get_opclass_family(opclass);
-			pInfer->inferopcinputtype = get_opclass_input_type(opclass);
-		}
+			pInfer->inferopclass = get_opclass_oid(BTREE_AM_OID,
+												   ielem->opclass, false);
 
 		result = lappend(result, pInfer);
 	}

src/include/nodes/primnodes.h

@@ -1198,8 +1198,7 @@ typedef struct InferenceElem
 	Expr		xpr;
 	Node	   *expr;				/* expression to infer from, or NULL */
 	Oid			infercollid;		/* OID of collation, or InvalidOid */
-	Oid			inferopfamily;		/* OID of att opfamily, or InvalidOid */
-	Oid			inferopcinputtype;	/* OID of att input type, or InvalidOid */
+	Oid			inferopclass;		/* OID of att opclass, or InvalidOid */
 } InferenceElem;
 
 /*--------------------