error[E0599]: the method `as_display` exists for reference `&<T as FromStr>::Err`, but its trait bounds were not satisfied
       --> tests/test_generics.rs:178:13
        |
    178 |     #[error("couldn't parse entry: {0}")]
        |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^ method cannot be called on `&<T as FromStr>::Err` due to unsatisfied trait bounds
        |
        = note: the following trait bounds were not satisfied:
                `<T as FromStr>::Err: std::fmt::Display`
                which is required by `&<T as FromStr>::Err: AsDisplay<'_>`

Generate trait bounds on associated types

Add feature gate to tests that use std

    warning: unused import: `std::path::PathBuf`
     --> tests/test_expr.rs:4:5
      |
    4 | use std::path::PathBuf;
      |     ^^^^^^^^^^^^^^^^^^
      |
      = note: `#[warn(unused_imports)]` on by default

Add CI step to test with "std" disabled