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, 4 insertions, 13 deletions

diff --git a/src/backend/utils/adt/datetime.c b/src/backend/utils/adt/datetime.c
index b5b117a8ca7..8afda0e5d22 100644
--- a/src/backend/utils/adt/datetime.c
+++ b/src/backend/utils/adt/datetime.c
@@ -4983,19 +4983,10 @@ pg_timezone_abbrevs(PG_FUNCTION_ARGS)
 		*pindex = 0;
 		funcctx->user_fctx = (void *) pindex;
 
-		/*
-		 * build tupdesc for result tuples. This must match this function's
-		 * pg_proc entry!
-		 */
-		tupdesc = CreateTemplateTupleDesc(3);
-		TupleDescInitEntry(tupdesc, (AttrNumber) 1, "abbrev",
-						   TEXTOID, -1, 0);
-		TupleDescInitEntry(tupdesc, (AttrNumber) 2, "utc_offset",
-						   INTERVALOID, -1, 0);
-		TupleDescInitEntry(tupdesc, (AttrNumber) 3, "is_dst",
-						   BOOLOID, -1, 0);
-
-		funcctx->tuple_desc = BlessTupleDesc(tupdesc);
+		if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
+			elog(ERROR, "return type must be a row type");
+		funcctx->tuple_desc = tupdesc;
+
 		MemoryContextSwitchTo(oldcontext);
 	}