Clap derive expansion no longer works on stable

[pksunkara]

Code

Clap has the following test at clap_derive/tests/nested.rs:

use clap::Clap;

#[test]
fn use_option() {
    macro_rules! expand_ty {
        ($name:ident: $ty:ty) => {
            #[derive(Clap)]
            struct Outer {
                #[clap(short, long)]
                #[allow(dead_code)]
                $name: $ty,
            }
        };
    }

    expand_ty!(my_field: Option<String>);
}

As you can see from the latest master CI, it fails to compile on stable

Version it worked on

It most recently worked on: Successfully compiles and runs on 1.46.0

Version with regression

rustc --version --verbose:

rustc 1.48.0 (7eac88abb 2020-11-16)

[pksunkara]

Weirdly, when I use my mac to test this locally, it works.

→ rustup show active-toolchain
stable-x86_64-apple-darwin (default)
→ cargo test -p clap_derive --test nested --features "wrap_help yaml regex"
   Compiling ....
    Finished test [unoptimized + debuginfo] target(s) in 55.55s
     Running target/debug/deps/nested-55411ec307e7b9f1

running 1 test
test use_option ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

NOTE: macos stable fails on CI, so I don't think this is an OS issue.

On EC2, it fails with the above error from the CI:

→ rustup show active-toolchain
stable-x86_64-unknown-linux-gnu (default)
→ cargo test -p clap_derive --test nested --features "wrap_help yaml regex"
error[E0425]: cannot find value `arg_matches` in this scope
Error:   --> clap_derive/tests/nested.rs:32:26
   |
32 |     expand_ty!(my_field: Option<String>);
   |                          ^^^^^^ not found in this scope

[pksunkara]

Pinging @petrochenkov because I suspect this is an issue with macro expansion. I tried cargo expand on the EC2 instance to check the output, but the code it had generated had no issues at all and successfully compiled.

Which is also the reason I couldn't generate a minimal reproducible example. I have no idea what's causing this.

[jyn514]

This works on 1.47 and breaks on 1.48.

[jyn514]

searched nightlies: from nightly-2020-07-11 to nightly-2020-11-28
regressed nightly: nightly-2020-09-12
searched commits: from a1947b3 to 9911160
regressed commit: 94b4de0

bisected with cargo-bisect-rustc v0.5.2

Host triple: x86_64-unknown-linux-gnu
Reproduce with:

cargo bisect-rustc -v --script ./test.sh --preserve --start 2020-07-11 

where test.sh is

#!/bin/sh
cargo test -p clap_derive --test nested

[jyn514]

cc @Aaron1011 - #75800 broke clap.

[Aaron1011]

This is due to a bug in how clap uses quote_spanned!. When #75800 was merged, we started preserving hygiene information in more cases, exposing the bug,

I've opened clap-rs/clap#2231 to fix the issue