Unclear error message: cannot convert argument to native type: failed to convert from int because of...

[timfennis]

When you call a native method from Andy C code that requires a usize you get a pretty unhelpful error if the integer value could not be converted into a usize because it was negative.

[1,2,3].truncate(-1);

Results in the unhelpful error:

cannot convert argument to native type: failed to convert from int because of: 'out of range integral type conversion attempted'

A more helpful error would point out that negative numbers aren't allowed here.