Have LookupFuncName accept NULL argtypes for 0 args

Prior to this change, it requires to be passed a valid pointer just to
be able to pass it to a zero-byte memcmp, per 0a52d378b0.  Given the
strange resulting code in callsites, it seems better to test for the
case specifically and remove the requirement.

Reported-by: Ranier Vilela
Discussion: https://postgr.es/m/MN2PR18MB2927F24692485D754794F01BE3740@MN2PR18MB2927.namprd18.prod.outlook.com
Discussion: https://postgr.es/m/MN2PR18MB2927F6873DF2774A505AC298E3740@MN2PR18MB2927.namprd18.prod.outlook.com

src/backend/commands/event_trigger.c

@@ -171,7 +171,6 @@ CreateEventTrigger(CreateEventTrigStmt *stmt)
 	HeapTuple	tuple;
 	Oid			funcoid;
 	Oid			funcrettype;
-	Oid			fargtypes[1];	/* dummy */
 	Oid			evtowner = GetUserId();
 	ListCell   *lc;
 	List	   *tags = NULL;
@@ -237,7 +236,7 @@ CreateEventTrigger(CreateEventTrigStmt *stmt)
 						stmt->trigname)));
 
 	/* Find and validate the trigger function. */
-	funcoid = LookupFuncName(stmt->funcname, 0, fargtypes, false);
+	funcoid = LookupFuncName(stmt->funcname, 0, NULL, false);
 	funcrettype = get_func_rettype(funcoid);
 	if (funcrettype != EVTTRIGGEROID)
 		ereport(ERROR,

src/backend/commands/foreigncmds.c

@@ -475,13 +475,12 @@ static Oid
 lookup_fdw_handler_func(DefElem *handler)
 {
 	Oid			handlerOid;
-	Oid			funcargtypes[1];	/* dummy */
 
 	if (handler == NULL || handler->arg == NULL)
 		return InvalidOid;
 
 	/* handlers have no arguments */
-	handlerOid = LookupFuncName((List *) handler->arg, 0, funcargtypes, false);
+	handlerOid = LookupFuncName((List *) handler->arg, 0, NULL, false);
 
 	/* check that handler has correct return type */
 	if (get_func_rettype(handlerOid) != FDW_HANDLEROID)

src/backend/commands/proclang.c

@@ -105,7 +105,7 @@ CreateProceduralLanguage(CreatePLangStmt *stmt)
 		 * return type.
 		 */
 		funcname = SystemFuncName(pltemplate->tmplhandler);
-		handlerOid = LookupFuncName(funcname, 0, funcargtypes, true);
+		handlerOid = LookupFuncName(funcname, 0, NULL, true);
 		if (OidIsValid(handlerOid))
 		{
 			funcrettype = get_func_rettype(handlerOid);
@@ -263,7 +263,7 @@ CreateProceduralLanguage(CreatePLangStmt *stmt)
 		 * Lookup the PL handler function and check that it is of the expected
 		 * return type
 		 */
-		handlerOid = LookupFuncName(stmt->plhandler, 0, funcargtypes, false);
+		handlerOid = LookupFuncName(stmt->plhandler, 0, NULL, false);
 		funcrettype = get_func_rettype(handlerOid);
 		if (funcrettype != LANGUAGE_HANDLEROID)
 		{

src/backend/commands/trigger.c

@@ -179,7 +179,6 @@ CreateTrigger(CreateTrigStmt *stmt, const char *queryString,
 	ScanKeyData key;
 	Relation	pgrel;
 	HeapTuple	tuple;
-	Oid			fargtypes[1];	/* dummy */
 	Oid			funcrettype;
 	Oid			trigoid;
 	char		internaltrigname[NAMEDATALEN];
@@ -690,7 +689,7 @@ CreateTrigger(CreateTrigStmt *stmt, const char *queryString,
 	 * Find and validate the trigger function.
 	 */
 	if (!OidIsValid(funcoid))
-		funcoid = LookupFuncName(stmt->funcname, 0, fargtypes, false);
+		funcoid = LookupFuncName(stmt->funcname, 0, NULL, false);
 	if (!isInternal)
 	{
 		aclresult = pg_proc_aclcheck(funcoid, GetUserId(), ACL_EXECUTE);

src/backend/parser/parse_func.c

@@ -2035,8 +2035,8 @@ LookupFuncNameInternal(List *funcname, int nargs, const Oid *argtypes,
 {
 	FuncCandidateList clist;
 
-	/* Passing NULL for argtypes is no longer allowed */
+	/* NULL argtypes allowed for nullary functions only */
-	Assert(argtypes);
+	Assert(argtypes != NULL || nargs == 0);
 
 	/* Always set *lookupError, to forestall uninitialized-variable warnings */
 	*lookupError = FUNCLOOKUP_NOSUCHFUNC;
@@ -2070,7 +2070,9 @@ LookupFuncNameInternal(List *funcname, int nargs, const Oid *argtypes,
 	 */
 	while (clist)
 	{
-		if (memcmp(argtypes, clist->args, nargs * sizeof(Oid)) == 0)
+		/* if nargs==0, argtypes can be null; don't pass that to memcmp */
+		if (nargs == 0 ||
+			memcmp(argtypes, clist->args, nargs * sizeof(Oid)) == 0)
 			return clist->oid;
 		clist = clist->next;
 	}

src/pl/tcl/pltcl.c

@@ -592,7 +592,6 @@ call_pltcl_start_proc(Oid prolang, bool pltrusted)
 	const char *gucname;
 	ErrorContextCallback errcallback;
 	List	   *namelist;
-	Oid			fargtypes[1];	/* dummy */
 	Oid			procOid;
 	HeapTuple	procTup;
 	Form_pg_proc procStruct;
@@ -616,7 +615,7 @@ call_pltcl_start_proc(Oid prolang, bool pltrusted)
 
 	/* Parse possibly-qualified identifier and look up the function */
 	namelist = stringToQualifiedNameList(start_proc);
-	procOid = LookupFuncName(namelist, 0, fargtypes, false);
+	procOid = LookupFuncName(namelist, 0, NULL, false);
 
 	/* Current user must have permission to call function */
 	aclresult = pg_proc_aclcheck(procOid, GetUserId(), ACL_EXECUTE);