src/test/ui/proc-macro/proc-macro-gates2.rs

// aux-build:test-macros.rs

#![feature(stmt_expr_attributes)]

#[macro_use]
extern crate test_macros;

// NB. these errors aren't the best errors right now, but they're definitely
// intended to be errors. Somehow using a custom attribute in these positions
// should either require a feature gate or not be allowed on stable.

fn _test6<#[empty_attr] T>() {}
//~^ ERROR: unknown to the compiler

fn _test7() {
    match 1 {
        #[empty_attr] //~ ERROR: unknown to the compiler
        0 => {}
        _ => {}
    }
}

fn main() {
}