Compiler error due to `structopt` attributes

[fpoli]

The latest nightly Rust generates an error when using #[structopt(..)] arguments:

error[E0658]: The attribute `structopt` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
  --> src/cli.rs:27:5
   |
27 |     #[structopt(long = "graphviz_file")]
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = help: add #![feature(custom_attribute)] to the crate attributes to enable

See https://travis-ci.org/rust-lang-nursery/polonius/builds/405315425 for a full example.

It would be useful to mention in the readme the #![feature(custom_attribute)].

[TeXitoi]

Looking at the problem, the bad hint is tracked in rust-lang/rust#52469

I can't find a #[macro_use] before your extern crate structopt in polonius, and I suspect that's the problem, because the first error is

error: cannot find derive macro `StructOpt` in this scope
  --> src/cli.rs:11:10
   |
11 | #[derive(StructOpt, Debug)]
   |          ^^^^^^^^^

I suspect you must add #[macro_use] here: https://github.com/rust-lang-nursery/polonius/blob/master/src/lib.rs#L15

Does it fix your problem?

[TeXitoi]

Strange that it worked before, maybe proc_macro feature was lazy on importing the macro?

[fpoli]

Adding #[macro_use] fixes the issue, thanks!