Change in macro output between 1.37.0 and 1.38.0 #65207
Description
The following code changed output between Rust 1.37.0 and 1.38.0:
macro_rules! call_a_or_b_on_tail {
((a: $a:expr, b: $b:expr), call a: $($tail:tt)*) => {
$a(stringify!($($tail)*))
};
((a: $a:expr, b: $b:expr), call b: $($tail:tt)*) => {
$b(stringify!($($tail)*))
};
($ab:tt, $_skip:tt $($tail:tt)*) => {
call_a_or_b_on_tail!($ab, $($tail)*)
};
}
fn compute_len(s: &str) -> usize {
s.len()
}
fn main() {
println!(
"{expr1}\n{expr2}",
expr1 = call_a_or_b_on_tail!(
(a: compute_len, b: zero),
and now, to justify the existence of two paths
we will also call a: its input should somehow
be self-referential, so let's make it return
some ninety one!
),
expr2 = call_a_or_b_on_tail!(
(a: compute_len, b: zero),
and now, to justify the existence of two paths
we will also call a: its input should somehow
be self-referential, so let's make it return
some ninety "(\"()"nine!
),
);
}djc-ing master regress $ cargo run
Compiling regress v0.1.0 (/Users/djc/src/regress)
Finished dev [unoptimized + debuginfo] target(s) in 0.35s
Running `target/debug/regress`
90
98
djc-ing master regress $ cargo +1.37.0 run
Compiling regress v0.1.0 (/Users/djc/src/regress)
Finished dev [unoptimized + debuginfo] target(s) in 0.30s
Running `target/debug/regress`
91
99
Playground: https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=6f67da3ab63067c8186ca702fe1c1910