ICE with complex custom derive

[Xanewok]

Originally created by @nrc (rust-dev-tools/rls-analysis#83):

See https://github.com/DanielKeep/rust-conv/blob/master/src/errors.rs#L227-L256

custom_derive!{
    /**
    A general error enumeration that subsumes all other conversion errors.
    This exists primarily as a "catch-all" for reliably unifying various different kinds of conversion errors.
    */
    #[derive(
        Copy, Clone, Eq, PartialEq, Ord, PartialOrd,
        IntoInner, DummyDebug, FromNoError,
        EnumDesc(
            NegOverflow => "conversion resulted in negative overflow",
            PosOverflow => "conversion resulted in positive overflow",
            Unrepresentable => "could not convert unrepresentable value",
        ),
        FromName(Unrepresentable),
        FromName(NegOverflow),
        FromName(PosOverflow),
        FromRemap(RangeError(NegOverflow, PosOverflow))
    )]
    pub enum GeneralError<T> {
        /// Input was too negative for the target type.
        NegOverflow(T),

        /// Input was too positive for the target type.
        PosOverflow(T),

        /// Input was not representable in the target type.
        Unrepresentable(T),
    }
}

I think the ICE is happening when compiling the conv crate

[Xanewok]

Just tested this and the ICE is gone now, so closing.