When I call a function with insufficient arguments, rustc just says the number of arguments is wrong. > <anon>:4:5: 4:26 error: this function takes 1 parameter but 0 parameters were supplied [E0061] > <anon>:4 std::fs::File::open(); > ^~~~~~~~~~~~~~~~~~~~~ This would be much more helpful if it said which arguments, and what they are, e.g.: > error: The `path` argument was not supplied to the `open` function or at least show the funcition definition in a note: > <anon>:4:5: 4:26 error: this function takes 1 parameter but 0 parameters were supplied [E0061] > <anon>:4 std::fs::File::open(); > note: `fn open<P: AsRef<Path>>(path: P) -> Result<File>` Similar problem applies to E0050 ("error: method `foo` has 1 parameter but the declaration in trait `bar` has 2"). --- rustc 1.10.0-nightly (2b79e05a0 2016-05-13)