* Allow empty argument lists in function definitions (e.g., `{}:

bla').  Also allow trailing commas (`{x, y,}: ...') as a unintented
  consequence.  Hopefully the reduce/reduce conflict won't cause any
  problems.

src/libexpr/parser.y

@@ -249,6 +249,7 @@ expr_list
 formals
   : formal ',' formals { $$ = ATinsert($3, $1); } /* idem - right recursive */
   | formal { $$ = ATinsert(ATempty, $1); }
+  | { $$ = ATempty; }
   ;
 
 formal

tests/lang/eval-okay-empty-args.exp

@@ -0,0 +1 @@
+Str("ab",[])

tests/lang/eval-okay-empty-args.nix

@@ -0,0 +1 @@
+({}: {x,y,}: "${x}${y}") {} {x = "a"; y = "b";}