ICE: format_args!() macro expansion fails with "index out of bounds: the len is 1 but the index is 2"

[maroider]

This failure was encountered in time, specifically with this macro invocation.

Code

fn main() {
    let value = 1.0;
    let width = 20;
    let digits_after_decimal = 10;
    format_args!(
        "{value:0>width$.digits_after_decimal$}",
        value = value,
        width = width,
        digits_after_decimal = digits_after_decimal,
    );
}

Meta

rustc +nightly-2022-07-15 --version --verbose:

cargo 1.64.0-nightly (8827baaa7 2022-07-14)
release: 1.64.0-nightly
commit-hash: 8827baaa781b37872134c1ba692a6f0aeb37890e
commit-date: 2022-07-14
host: x86_64-unknown-linux-gnu
libgit2: 1.4.2 (sys:0.14.2 vendored)
libcurl: 7.83.1-DEV (sys:0.4.55+curl-7.83.1 vendored ssl:OpenSSL/1.1.1n)
os: Arch Linux Rolling Release [64-bit]

I also checked the nightly-2022-07-14 toolchain, which works fine, as well as the nightly-2022-07-16 toolchain, which still has the ICE.

Error output

thread 'rustc' panicked at 'index out of bounds: the len is 1 but the index is 2', compiler/rustc_builtin_macros/src/format.rs:1001:28

Backtrace

stack backtrace:
   0: rust_begin_unwind
             at /rustc/c2f428d2f3340a0e7d995f4726223db91b93704c/library/std/src/panicking.rs:584:5
   1: core::panicking::panic_fmt
             at /rustc/c2f428d2f3340a0e7d995f4726223db91b93704c/library/core/src/panicking.rs:142:14
   2: core::panicking::panic_bounds_check
             at /rustc/c2f428d2f3340a0e7d995f4726223db91b93704c/library/core/src/panicking.rs:84:5
   3: rustc_builtin_macros::format::expand_preparsed_format_args
   4: rustc_builtin_macros::format::expand_format_args_impl
   5: <rustc_expand::expand::MacroExpander>::fully_expand_fragment
   6: <rustc_expand::expand::MacroExpander>::expand_crate
   7: <rustc_session::session::Session>::time::<core::result::Result<rustc_ast::ast::Crate, rustc_errors::ErrorGuaranteed>, rustc_interface::passes::configure_and_expand::{closure#1}>
   8: rustc_interface::passes::configure_and_expand
   9: <rustc_interface::queries::Queries>::expansion
  10: <rustc_interface::interface::Compiler>::enter::<rustc_driver::run_compiler::{closure#1}::{closure#2}, core::result::Result<core::option::Option<rustc_interface::queries::Linker>, rustc_errors::ErrorGuaranteed>>
  11: rustc_span::with_source_map::<core::result::Result<(), rustc_errors::ErrorGuaranteed>, rustc_interface::interface::create_compiler_and_run<core::result::Result<(), rustc_errors::ErrorGuaranteed>, rustc_driver::run_compiler::{closure#1}>::{closure#1}>
  12: rustc_interface::interface::create_compiler_and_run::<core::result::Result<(), rustc_errors::ErrorGuaranteed>, rustc_driver::run_compiler::{closure#1}>
  13: <scoped_tls::ScopedKey<rustc_span::SessionGlobals>>::set::<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_errors::ErrorGuaranteed>, rustc_driver::run_compiler::{closure#1}>::{closure#0}, core::result::Result<(), rustc_errors::ErrorGuaranteed>>

[maroider]

Welp, just noticed there's already a pinned issue for this (#99261)