[ICE]: rustfmt panic on "macro_rules !" span on nightly

Hello,

I am a maintainer of apollo-rs, and we encountered a panic in the nightly formatter when a macro_rules definition has a space before the ! character. This does not panic on the latest stable version. I have attached the full ICE report from that repository at the bottom of this issue.

Code

macro_rules ! say_hello {
    () => {
        println!("Hello!")
    };
}

fn main() {
    say_hello!()
}

Configuration

rustfmt cli options used (if applicable):

$ cargo +nightly fmt -- --check

rustfmt configuration file (e.g. rustfmt.toml, if applicable):

None

Reproduction Steps

Author a macro, but put a space between macro_rules and the following !
Format with the nightly formatter

Error output

thread 'main' panicked at src/tools/rustfmt/src/source_map.rs:31:13:
bad span: `macro_rules!`: `macro_rules ! say_hello {
    () => {
        println!("Hello!")
    };
}`

Backtrace

stack backtrace:
   0:        0x10b4343c0 - <std[ee75d77504d5cc2c]::backtrace::Backtrace>::create
   1:        0x1092edc6c - std[ee75d77504d5cc2c]::panicking::update_hook::<alloc[45a93d76fd929ce]::boxed::Box<rustc_driver_impl[58d2776b959ed623]::install_ice_hook::{closure#1}>>::{closure#0}
   2:        0x10b448600 - std[ee75d77504d5cc2c]::panicking::panic_with_hook
   3:        0x10b429998 - std[ee75d77504d5cc2c]::panicking::panic_handler::{closure#0}
   4:        0x10b421818 - std[ee75d77504d5cc2c]::sys::backtrace::__rust_end_short_backtrace::<std[ee75d77504d5cc2c]::panicking::panic_handler::{closure#0}, !>
   5:        0x10b42aec0 - __rustc[fc4642eee87af86]::rust_begin_unwind
   6:        0x10b513154 - core[72355cdabd4545b3]::panicking::panic_fmt
   7:        0x103019a9c - <rustfmt_nightly[c40fde2e22d7a0d5]::visitor::SnippetProvider as rustfmt_nightly[c40fde2e22d7a0d5]::source_map::SpanUtils>::span_after::{closure#0}
   8:        0x102f7d0a0 - rustfmt_nightly[c40fde2e22d7a0d5]::macros::rewrite_macro_def
   9:        0x102f177b4 - <rustfmt_nightly[c40fde2e22d7a0d5]::visitor::FmtVisitor>::visit_item
  10:        0x102f50f14 - <rustfmt_nightly[c40fde2e22d7a0d5]::visitor::FmtVisitor>::visit_items_with_reordering
  11:        0x102f1b840 - <rustfmt_nightly[c40fde2e22d7a0d5]::visitor::FmtVisitor>::walk_mod_items
  12:        0x102ea7980 - <scoped_tls[c95850a21232a508]::ScopedKey<rustc_span[c94f91a8dd5c03e2]::SessionGlobals>>::with::<<rustfmt_nightly[c40fde2e22d7a0d5]::Session<std[ee75d77504d5cc2c]::io::stdio::Stdout>>::format_input_inner::{closure#0}, core[72355cdabd4545b3]::result::Result<rustfmt_nightly[c40fde2e22d7a0d5]::FormatReport, rustfmt_nightly[c40fde2e22d7a0d5]::ErrorKind>>
  13:        0x102ea3db0 - rustfmt[a53a59d609b04279]::format_and_emit_report::<std[ee75d77504d5cc2c]::io::stdio::Stdout>
  14:        0x102eb4e58 - rustfmt[a53a59d609b04279]::execute
  15:        0x102eb1380 - rustfmt[a53a59d609b04279]::main
  16:        0x102eafba4 - std[ee75d77504d5cc2c]::sys::backtrace::__rust_begin_short_backtrace::<fn(), ()>
  17:        0x102eb01fc - std[ee75d77504d5cc2c]::rt::lang_start::<()>::{closure#0}
  18:        0x10b446af8 - std[ee75d77504d5cc2c]::rt::lang_start_internal
  19:        0x102ebd1e8 - _main

rustc-ice-2026-07-27T13_57_27-23413.txt

@ytmimi

@ytmimi since the fix was merged a while ago. Shouldn't it work again on the nightly builds?

We need to sync rust-lang/rustfmt with rust-lang/rust before the change goes out on nightly

The bug seems to have been released in the Aug 7 nightly, but the fix wasn't. How come the fix didn't make it in?

@robertbastian

@robertbastian see my last comment. We haven't synced rust-lang/rustfmt back up with rust-lang/rust yet. That needs to happen before this fix goes out on nightly.

Is there a timeline for when this will happen?

Is there a timeline for when this will happen?

Seems to have happened 8h ago. https://github.com/rust-lang/rust/tree/main/src/tools/rustfmt

The failure still happens on nightly, and seems to have made it into beta now.

@rust-lang/release This fix should be backported into beta ASAP.

Seems to have happened 8h ago. https://github.com/rust-lang/rust/tree/main/src/tools/rustfmt

I don't think that's a sync.

Manual sync of just one PR: rust-lang/rust#161370

This fix should be backported into beta ASAP.

From local testing, it looks like this bug is in Rust 1.99+ today, so the backport needs to land on rust-lang/rust beta in the next ~5 weeks.

Rollup merge of rust-lang#161370 - Manishearth:rustfmt-macro-fix, r=y…

Unrolled build for #161370 in rollup 161434

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[ICE]: rustfmt panic on "macro_rules !" span on nightly #6985

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[ICE]: rustfmt panic on "macro_rules !" span on nightly #6985

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royb3 commented on Aug 3, 2026

ytmimi commented on Aug 3, 2026

robertbastian commented on Aug 10, 2026

ytmimi commented on Aug 10, 2026

robertbastian commented on Aug 17, 2026

royb3 commented on Aug 17, 2026

robertbastian commented on Aug 19, 2026

Manishearth commented on Aug 19, 2026

Manishearth commented on Aug 19, 2026

Mark-Simulacrum commented on Aug 19, 2026

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