Cannot use stringify! within paste::item! in a #[doc] attribute

[ilyvion]

This may be an odd edge case, but I want to have this bit of code within a macro:

paste::item! {
    /// The error type returned when a checked
    #[doc = $name_str]
    /// type conversion fails.
    #[derive(Debug, Copy, Clone, Eq, PartialEq)]
    pub enum [< TryFrom $name Error >] {
        /// The error type returned when a checked integral type conversion fails.
        TryFromIntError(TryFromIntError),
        /// The error type returned when a floating point value is outside the range
        /// of the integer type it needs to be converted to.
        FloatToInt,
    }
    impl From<TryFromIntError> for [< TryFrom $name Error >] {
        fn from(e: TryFromIntError) -> Self {
            Self::TryFromIntError(e)
        }
    }
}

It gives this compiler error:

error: unexpected token: `stringify`
   --> src\base\def_macro.rs:714:9
    |
714 | /         paste::item! {
715 | |             /// The error type returned when a checked
716 | |             #[doc = $name_str]
717 | |             /// type conversion fails.
...   |
730 | |             }
731 | |         }
    | |_________^
    | 
   ::: src\base.rs:40:1

The $name_str is passed into this invocation as stringify!($name). This works just fine if done outside of a paste::item!, so there must be something going on in the interaction between paste::item!, stringify! and/or #[doc].

It does not work with #[doc = stringify!($name)] either (same exact error), but #[doc = "a regular string"] works just fine.

[dtolnay]

I published 0.1.13 with a fix.

[ilyvion]

Thanks, that was fast! And your fix works like a charm. 😄

[ilyvion]

It seems like this issue (or at least, a related one) has reared its ugly head again in the latest Rust 1.50. You can see it in action on this playground.

Related discussion @ rust-lang/rust#78835.

[ilyvion]

Actually, some more in-depth research tells me that this seems entirely unrelated to that Rust issue/version. I just noticed that the issue goes away if I go back to paste v0.1.14, but is present in all versions from v0.1.15 onwards except in 1.0.3, where it works, but then 1.0.4 breaks it again.