Add some opfamily support functions to lsyscache.c

Add get_opfamily_method() and get_opfamily_member_for_cmptype() in
lsyscache.c.  No callers yet, but we'll add some soon.  This is part
of generalizing some parts of the code away from having btree
hardcoded and use CompareType instead.

Author: Mark Dilger <mark.dilger@enterprisedb.com>
Discussion: https://www.postgresql.org/message-id/flat/E72EAA49-354D-4C2E-8EB9-255197F55330@enterprisedb.com

src/backend/utils/cache/lsyscache.c

@@ -184,6 +184,28 @@ get_opfamily_member(Oid opfamily, Oid lefttype, Oid righttype,
 	return result;
 }
 
+/*
+ * get_opfamily_member_for_cmptype
+ *		Get the OID of the operator that implements the specified comparison
+ *		type with the specified datatypes for the specified opfamily.
+ *
+ * Returns InvalidOid if there is no mapping for the comparison type or no
+ * pg_amop entry for the given keys.
+ */
+Oid
+get_opfamily_member_for_cmptype(Oid opfamily, Oid lefttype, Oid righttype,
+								CompareType cmptype)
+{
+	Oid			opmethod;
+	StrategyNumber strategy;
+
+	opmethod = get_opfamily_method(opfamily);
+	strategy = IndexAmTranslateCompareType(cmptype, opmethod, opfamily, true);
+	if (!strategy)
+		return InvalidOid;
+	return get_opfamily_member(opfamily, lefttype, righttype, strategy);
+}
+
 /*
  * get_ordering_op_properties
  *		Given the OID of an ordering operator (a btree "<" or ">" operator),
@@ -1288,6 +1310,28 @@ get_opclass_method(Oid opclass)
 
 /*				---------- OPFAMILY CACHE ----------					 */
 
+/*
+ * get_opfamily_method
+ *
+ *		Returns the OID of the index access method the opfamily is for.
+ */
+Oid
+get_opfamily_method(Oid opfid)
+{
+	HeapTuple	tp;
+	Form_pg_opfamily opfform;
+	Oid			result;
+
+	tp = SearchSysCache1(OPFAMILYOID, ObjectIdGetDatum(opfid));
+	if (!HeapTupleIsValid(tp))
+		elog(ERROR, "cache lookup failed for operator family %u", opfid);
+	opfform = (Form_pg_opfamily) GETSTRUCT(tp);
+
+	result = opfform->opfmethod;
+	ReleaseSysCache(tp);
+	return result;
+}
+
 char *
 get_opfamily_name(Oid opfid, bool missing_ok)
 {

src/include/utils/lsyscache.h

@@ -14,6 +14,7 @@
 #define LSYSCACHE_H
 
 #include "access/attnum.h"
+#include "access/cmptype.h"
 #include "access/htup.h"
 #include "nodes/pg_list.h"
 
@@ -74,6 +75,8 @@ extern void get_op_opfamily_properties(Oid opno, Oid opfamily, bool ordering_op,
 									   Oid *righttype);
 extern Oid	get_opfamily_member(Oid opfamily, Oid lefttype, Oid righttype,
 								int16 strategy);
+extern Oid	get_opfamily_member_for_cmptype(Oid opfamily, Oid lefttype, Oid righttype,
+											CompareType cmptype);
 extern bool get_ordering_op_properties(Oid opno,
 									   Oid *opfamily, Oid *opcintype, int16 *strategy);
 extern Oid	get_equality_op_for_ordering_op(Oid opno, bool *reverse);
@@ -108,6 +111,7 @@ extern Oid	get_opclass_input_type(Oid opclass);
 extern bool get_opclass_opfamily_and_input_type(Oid opclass,
 												Oid *opfamily, Oid *opcintype);
 extern Oid	get_opclass_method(Oid opclass);
+extern Oid	get_opfamily_method(Oid opfid);
 extern char *get_opfamily_name(Oid opfid, bool missing_ok);
 extern RegProcedure get_opcode(Oid opno);
 extern char *get_opname(Oid opno);