Switch some system functions to use get_call_result_type()

This shaves some code by replacing the combinations of
CreateTemplateTupleDesc()/TupleDescInitEntry() hardcoding a mapping of
the attributes listed in pg_proc.dat by get_call_result_type() to build
the TupleDesc needed for the rows generated.

get_call_result_type() is more expensive than the former style, but this
removes some duplication with the lists of OUT parameters (pg_proc.dat
and the attributes hardcoded in these code paths).  This is applied to
functions that are not considered as critical (aka that could be called
repeatedly for monitoring purposes).

Author: Bharath Rupireddy
Reviewed-by: Robert Haas, Álvaro Herrera, Tom Lane, Michael Paquier
Discussion: https://postgr.es/m/CALj2ACV23HW5HP5hFjd89FNS-z5X8r2jNXdMXcpN2BgTtKd87w@mail.gmail.com

1 files changed, 2 insertions, 4 deletions

diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index a95f73ec796..81f262a5f46 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -291,10 +291,8 @@ pg_visibility_map_summary(PG_FUNCTION_ARGS)
 		ReleaseBuffer(vmbuffer);
 	relation_close(rel, AccessShareLock);
 
-	tupdesc = CreateTemplateTupleDesc(2);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 1, "all_visible", INT8OID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 2, "all_frozen", INT8OID, -1, 0);
-	tupdesc = BlessTupleDesc(tupdesc);
+	if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
+		elog(ERROR, "return type must be a row type");
 
 	values[0] = Int64GetDatum(all_visible);
 	values[1] = Int64GetDatum(all_frozen);