strange scoping issue when trying to use alloc::vec![]

[alex]

https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=74f146f90570f0e4bb9e2b957532290a

#![no_std]

extern crate alloc;

use alloc::vec::Vec;

pub fn f() -> Vec<u8> {
    let x = alloc::vec![
        0,
    ].into_boxed_slice();
    return x.to_vec();
}

   Compiling playground v0.0.1 (/playground)
error: cannot find macro `vec!` in this scope
  --> src/lib.rs:8:13
   |
8  |       let x = alloc::vec![
   |  _____________^
9  | |         0,
10 | |     ].into_boxed_slice();
   | |_____^
   |
   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

error: aborting due to previous error

error: Could not compile `playground`.

If I change the invocation to alloc::vec![] it has no trouble finding the invocation. I have no idea what to make of this.

[petrochenkov]

Fixed in #61629

[alex]

Thanks!

[petrochenkov]

The workaround is to remove the trailing comma after 0 inside vec![], then vec won't call itself recursively (which is causing the error).

[alex]

Yup, now that you've pointed it out it's completely clear what was happening :-/