Use PG_GETARG_TRANSACTIONID where appropriate

Some places were using PG_GETARG_UINT32 where PG_GETARG_TRANSACTIONID
would be more appropriate.  (Of course, they are the same internally,
so there is no externally visible effect.)  To do that, export
PG_GETARG_TRANSACTIONID outside of xid.c.  We also export
PG_RETURN_TRANSACTIONID for symmetry, even though there are currently
no external users.

Author: Ashutosh Bapat <ashutosh.bapat@2ndquadrant.com>
Discussion: https://www.postgresql.org/message-id/flat/d8f6bdd536df403b9b33816e9f7e0b9d@G08CNEXMBPEKD05.g08.fujitsu.local

src/backend/access/transam/commit_ts.c

@@ -404,7 +404,7 @@ error_commit_ts_disabled(void)
 Datum
 pg_xact_commit_timestamp(PG_FUNCTION_ARGS)
 {
-	TransactionId xid = PG_GETARG_UINT32(0);
+	TransactionId xid = PG_GETARG_TRANSACTIONID(0);
 	TimestampTz ts;
 	bool		found;
 
@@ -481,7 +481,7 @@ pg_last_committed_xact(PG_FUNCTION_ARGS)
 Datum
 pg_xact_commit_timestamp_origin(PG_FUNCTION_ARGS)
 {
-	TransactionId xid = PG_GETARG_UINT32(0);
+	TransactionId xid = PG_GETARG_TRANSACTIONID(0);
 	RepOriginId nodeid;
 	TimestampTz ts;
 	Datum		values[2];

src/backend/access/transam/multixact.c

@@ -3339,7 +3339,7 @@ pg_get_multixact_members(PG_FUNCTION_ARGS)
 		int			nmembers;
 		int			iter;
 	} mxact;
-	MultiXactId mxid = PG_GETARG_UINT32(0);
+	MultiXactId mxid = PG_GETARG_TRANSACTIONID(0);
 	mxact	   *multi;
 	FuncCallContext *funccxt;
 

src/backend/utils/adt/xid.c

@@ -23,9 +23,6 @@
 #include "utils/builtins.h"
 #include "utils/xid8.h"
 
-#define PG_GETARG_TRANSACTIONID(n)	DatumGetTransactionId(PG_GETARG_DATUM(n))
-#define PG_RETURN_TRANSACTIONID(x)	return TransactionIdGetDatum(x)
-
 #define PG_GETARG_COMMANDID(n)		DatumGetCommandId(PG_GETARG_DATUM(n))
 #define PG_RETURN_COMMANDID(x)		return CommandIdGetDatum(x)
 

src/include/fmgr.h

@@ -276,6 +276,7 @@ extern struct varlena *pg_detoast_datum_packed(struct varlena *datum);
 #define PG_GETARG_POINTER(n) DatumGetPointer(PG_GETARG_DATUM(n))
 #define PG_GETARG_CSTRING(n) DatumGetCString(PG_GETARG_DATUM(n))
 #define PG_GETARG_NAME(n)	 DatumGetName(PG_GETARG_DATUM(n))
+#define PG_GETARG_TRANSACTIONID(n)	DatumGetTransactionId(PG_GETARG_DATUM(n))
 /* these macros hide the pass-by-reference-ness of the datatype: */
 #define PG_GETARG_FLOAT4(n)  DatumGetFloat4(PG_GETARG_DATUM(n))
 #define PG_GETARG_FLOAT8(n)  DatumGetFloat8(PG_GETARG_DATUM(n))
@@ -360,6 +361,7 @@ extern struct varlena *pg_detoast_datum_packed(struct varlena *datum);
 #define PG_RETURN_POINTER(x) return PointerGetDatum(x)
 #define PG_RETURN_CSTRING(x) return CStringGetDatum(x)
 #define PG_RETURN_NAME(x)	 return NameGetDatum(x)
+#define PG_RETURN_TRANSACTIONID(x)	return TransactionIdGetDatum(x)
 /* these macros hide the pass-by-reference-ness of the datatype: */
 #define PG_RETURN_FLOAT4(x)  return Float4GetDatum(x)
 #define PG_RETURN_FLOAT8(x)  return Float8GetDatum(x)