Finish reverting commit 0a52d378b.

Apply the solution adopted in commit dcb7d3caf (ie, explicitly
don't call memcmp for a zero-length comparison) to func_get_detail()
as well, removing one other place where we were passing an
uninitialized array to a parse_func.c entry point.

Discussion: https://postgr.es/m/MN2PR18MB2927F24692485D754794F01BE3740@MN2PR18MB2927.namprd18.prod.outlook.com
Discussion: https://postgr.es/m/MN2PR18MB2927F6873DF2774A505AC298E3740@MN2PR18MB2927.namprd18.prod.outlook.com

src/backend/parser/parse_func.c

@@ -1397,9 +1397,6 @@ func_get_detail(List *funcname,
 	FuncCandidateList raw_candidates;
 	FuncCandidateList best_candidate;
 
-	/* Passing NULL for argtypes is no longer allowed */
-	Assert(argtypes);
-
 	/* initialize output arguments to silence compiler warnings */
 	*funcid = InvalidOid;
 	*rettype = InvalidOid;
@@ -1423,7 +1420,9 @@ func_get_detail(List *funcname,
 		 best_candidate != NULL;
 		 best_candidate = best_candidate->next)
 	{
-		if (memcmp(argtypes, best_candidate->args, nargs * sizeof(Oid)) == 0)
+		/* if nargs==0, argtypes can be null; don't pass that to memcmp */
+		if (nargs == 0 ||
+			memcmp(argtypes, best_candidate->args, nargs * sizeof(Oid)) == 0)
 			break;
 	}
 

src/backend/utils/adt/ruleutils.c

@@ -833,7 +833,6 @@ pg_get_triggerdef_worker(Oid trigid, bool pretty)
 	char	   *tgname;
 	char	   *tgoldtable;
 	char	   *tgnewtable;
-	Oid			argtypes[1];	/* dummy */
 	Datum		value;
 	bool		isnull;
 
@@ -1045,7 +1044,7 @@ pg_get_triggerdef_worker(Oid trigid, bool pretty)
 
 	appendStringInfo(&buf, "EXECUTE FUNCTION %s(",
 					 generate_function_name(trigrec->tgfoid, 0,
-											NIL, argtypes,
+											NIL, NULL,
 											false, NULL, EXPR_KIND_NONE));
 
 	if (trigrec->tgnargs > 0)