Code

We have a library that compiles fine on 1.47.0 but after uggrading to 1.48.0 the compilation hangs.

#![allow(unused)] macro_rules! declare_nats { ($prev:ty) => {}; ($prev:ty, $n:literal$(, $tail:literal)*) => { paste::item! { pub struct [<N $n>]($prev); } declare_nats!(Option<$prev>$(, $tail)*); }; (0, $($n:literal),+) => { pub struct N0; declare_nats!(N0, $($n),+); }; } declare_nats! { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64 } fn main() {}

This code-snippet above is reduced from the original code as much as I can. I'm having problems understanding exactly where the problem is coming from and any further modifications to reduce it haven't worked. It uses the "paste" crate, and I've tried a few different versions including the latest one but it doesn't make a difference .

I've been building it with cargo build at 1.47.0 and 1.48.0 to reproduce the issue which I got just by running rustup default

doesn't work on

rustc 1.48.0 (7eac88abb 2020-11-16) binary: rustc commit-hash: 7eac88abb2e57e752f3302f02be5f3ce3d7adfb4 commit-date: 2020-11-16 host: x86_64-unknown-linux-gnu release: 1.48.0 LLVM version: 11.0 

works on

rustc 1.47.0 (18bf6b4f0 2020-10-07) binary: rustc commit-hash: 18bf6b4f01a6feaf7259ba7cdae58031af1b7b39 commit-date: 2020-10-07 host: x86_64-unknown-linux-gnu release: 1.47.0 LLVM version: 11.0