hygiene: cannot find macro `foo!` in this scope

[tesuji]

This code (playpen) compiles on stable but not on nightly and beta:

macro_rules! foo {
    () => {
        "foo"
    };
}

macro_rules! bar {
    () => {
        foo!()
    };
}

fn main() {
    println!(bar!());
}

Standard Error

   Compiling playground v0.0.1 (/playground)
error: cannot find macro `foo!` in this scope
 --> src/main.rs:9:9
  |
9 |         foo!()
  |         ^^^

warning: unused macro definition
 --> src/main.rs:1:1
  |
1 | / macro_rules! foo {
2 | |     () => {
3 | |         "foo"
4 | |     };
5 | | }
  | |_^
  |
  = note: `#[warn(unused_macros)]` on by default

error: aborting due to previous error

error: Could not compile `playground`.

To learn more, run the command again with --verbose.

Edit: Removed concat! macro

Originally posted by @lzutao in #63460 (comment)

[tesuji]

@rustbot modify labels: A-macros A-resolve C-bug T-compiler

[tesuji]

I updated the snippet to remove the outer module.

[petrochenkov]

This is a regression from #63114 (cc @matthewjasper).
Slightly more minimized reproduction will look like this:

macro_rules! foo {
    () => {
        "foo"
    };
}

macro_rules! bar {
    () => {
        foo!()
    };
}

fn main() {
    format_args!(bar!()); // ERROR, `foo` is not found, happens because `format_args` is opaque now
}

format_args performs eager expansion on its arguments and hygienic context of foo produced by such expansion looks like it was produced by the opaque format_args for some reason, so it's resolved at format_args' definition site.

It maybe either some issue with hygiene infra interacting with eager expansion, but it also may be caused by incorrect spans produced by format_args.

[petrochenkov]

(I'm currently looking into the details.)

UPD: I have a fix locally, will submit tomorrow.

[petrochenkov]

Fixed in #63717.