When returning type "record", replace use of pgresultGetTupleDesc

with ReturnSetInfo->expectedDesc. This allows custom datatypes
(e.g. from tsearch2) to be returned at runtime. Previous behavior
depended on the type oid to match between the remote and local
database, which obviously doesn't work well for custom types.
Per report from Mark Gibson.

contrib/dblink/dblink.c

@@ -82,7 +82,6 @@ static char *quote_ident_cstr(char *rawstr);
 static int16 get_attnum_pk_pos(int16 *pkattnums, int16 pknumatts, int16 key);
 static HeapTuple get_tuple_of_interest(Oid relid, int16 *pkattnums, int16 pknumatts, char **src_pkattvals);
 static Oid	get_relid_from_relname(text *relname_text);
-static TupleDesc pgresultGetTupleDesc(PGresult *res);
 static char *generate_relation_name(Oid relid);
 
 /* Global */
@@ -395,6 +394,7 @@ dblink_fetch(PG_FUNCTION_ARGS)
 		StringInfo	str = makeStringInfo();
 		char	   *curname = NULL;
 		int			howmany = 0;
+		ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
 
 		if (PG_NARGS() == 3)
 		{
@@ -457,7 +457,16 @@ dblink_fetch(PG_FUNCTION_ARGS)
 		if (functyptype == 'c')
 			tupdesc = TypeGetTupleDesc(functypeid, NIL);
 		else if (functyptype == 'p' && functypeid == RECORDOID)
-			tupdesc = pgresultGetTupleDesc(res);
+		{
+			if (!rsinfo || !IsA(rsinfo, ReturnSetInfo))
+				ereport(ERROR,
+						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+						 errmsg("function returning record called in context "
+								"that cannot accept type record")));
+
+			/* get the requested return tuple description */
+			tupdesc = CreateTupleDescCopy(rsinfo->expectedDesc);
+		}
 		else
 			/* shouldn't happen */
 			elog(ERROR, "return type must be a row type");
@@ -550,6 +559,7 @@ dblink_record(PG_FUNCTION_ARGS)
 		char	   *sql = NULL;
 		char	   *conname = NULL;
 		remoteConn *rcon = NULL;
+		ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
 
 		/* create a function context for cross-call persistence */
 		funcctx = SRF_FIRSTCALL_INIT();
@@ -620,7 +630,16 @@ dblink_record(PG_FUNCTION_ARGS)
 			if (functyptype == 'c')
 				tupdesc = TypeGetTupleDesc(functypeid, NIL);
 			else if (functyptype == 'p' && functypeid == RECORDOID)
-				tupdesc = pgresultGetTupleDesc(res);
+			{
+				if (!rsinfo || !IsA(rsinfo, ReturnSetInfo))
+					ereport(ERROR,
+							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+							 errmsg("function returning record called in context "
+									"that cannot accept type record")));
+
+				/* get the requested return tuple description */
+				tupdesc = CreateTupleDescCopy(rsinfo->expectedDesc);
+			}
 			else
 				/* shouldn't happen */
 				elog(ERROR, "return type must be a row type");
@@ -1803,63 +1822,6 @@ get_relid_from_relname(text *relname_text)
 	return relid;
 }
 
-static TupleDesc
-pgresultGetTupleDesc(PGresult *res)
-{
-	int			natts;
-	AttrNumber	attnum;
-	TupleDesc	desc;
-	char	   *attname;
-	int32		atttypmod;
-	int			attdim;
-	bool		attisset;
-	Oid			atttypid;
-	int			i;
-
-	/*
-	 * allocate a new tuple descriptor
-	 */
-	natts = PQnfields(res);
-	if (natts < 1)
-		/* shouldn't happen */
-		elog(ERROR, "cannot create a description for empty results");
-
-	desc = CreateTemplateTupleDesc(natts, false);
-
-	attnum = 0;
-
-	for (i = 0; i < natts; i++)
-	{
-		/*
-		 * for each field, get the name and type information from the
-		 * query result and have TupleDescInitEntry fill in the attribute
-		 * information we need.
-		 */
-		attnum++;
-
-		attname = PQfname(res, i);
-		atttypid = PQftype(res, i);
-		atttypmod = PQfmod(res, i);
-
-		if (PQfsize(res, i) != get_typlen(atttypid))
-			ereport(ERROR,
-					(errcode(ERRCODE_MOST_SPECIFIC_TYPE_MISMATCH),
-					 errmsg("field size mismatch"),
-				errdetail("Size of remote field \"%s\" does not match " \
-						  "size of local type \"%s\".", attname,
-						  format_type_with_typemod(atttypid,
-												   atttypmod))));
-
-		attdim = 0;
-		attisset = false;
-
-		TupleDescInitEntry(desc, attnum, attname, atttypid,
-						   atttypmod, attdim, attisset);
-	}
-
-	return desc;
-}
-
 /*
  * generate_relation_name - copied from ruleutils.c
  *		Compute the name to display for a relation specified by OID