format! argument rustc panics with index out of bounds

[danw8]

Summary

Attempting to use the format argument N as the precision without correct number of arguments causes the compiler to panic.

I tried this code:

fn main() {
    let msg = format!("y: {0:.1$}", 1.234);
}

I expected to see an error message informing me of using format!() incorrectly

Instead, I got a compiler panic.

thread 'rustc' panicked at 'index out of bounds: the len is 1 but the index is 1', /rustc/4560ea788cb760f0a34127156c78e2552949f734/src/libcore/slice/mod.rs:2717:10
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.

error: internal compiler error: unexpected panic

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.39.0 (4560ea788 2019-11-04) running on x86_64-unknown-linux-gnu

note: compiler flags: -C codegen-units=1 -C debuginfo=2 --crate-type bin

note: some of the compiler flags provided by cargo are hidden

error: could not compile `playground`.

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

Meta

rustc --version --verbose:

thread 'rustc' panicked at 'index out of bounds: the len is 1 but the index is 1', /rustc/4560ea788cb760f0a34127156c78e2552949f734/src/libcore/slice/mod.rs:2717:10
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.

error: internal compiler error: unexpected panic

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.39.0 (4560ea788 2019-11-04) running on x86_64-unknown-linux-gnu

note: compiler flags: -C codegen-units=1 -C debuginfo=2 --crate-type bin

note: some of the compiler flags provided by cargo are hidden

error: could not compile `playground`.

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

Backtrace:

thread 'rustc' panicked at 'index out of bounds: the len is 1 but the index is 1', /rustc/4560ea788cb760f0a34127156c78e2552949f734/src/libcore/slice/mod.rs:2717:10
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/github.jparrowsec.cn-1ecc6299db9ec823/backtrace-0.3.37/src/backtrace/libunwind.rs:88
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/github.jparrowsec.cn-1ecc6299db9ec823/backtrace-0.3.37/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print_fmt
             at src/libstd/sys_common/backtrace.rs:76
   3: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
             at src/libstd/sys_common/backtrace.rs:60
   4: core::fmt::write
             at src/libcore/fmt/mod.rs:1030
   5: std::io::Write::write_fmt
             at src/libstd/io/mod.rs:1412
   6: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:64
   7: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:49
   8: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:196
   9: std::panicking::default_hook
             at src/libstd/panicking.rs:210
  10: rustc_driver::report_ice
  11: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:477
  12: std::panicking::continue_panic_fmt
             at src/libstd/panicking.rs:380
  13: rust_begin_unwind
             at src/libstd/panicking.rs:307
  14: core::panicking::panic_fmt
             at src/libcore/panicking.rs:85
  15: core::panicking::panic_bounds_check
             at src/libcore/panicking.rs:61
  16: syntax_ext::format::expand_preparsed_format_args
  17: syntax_ext::format::expand_format_args_impl
  18: <F as syntax::ext::base::TTMacroExpander>::expand
  19: syntax::ext::expand::MacroExpander::fully_expand_fragment
  20: syntax::ext::expand::MacroExpander::expand_crate
  21: rustc_interface::passes::configure_and_expand_inner::{{closure}}
  22: rustc::util::common::time
  23: rustc_interface::passes::configure_and_expand_inner
  24: rustc_interface::passes::configure_and_expand::{{closure}}
  25: rustc_data_structures::box_region::PinnedGenerator<I,A,R>::new
  26: rustc_interface::passes::configure_and_expand
  27: rustc_interface::queries::Query<T>::compute
  28: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::expansion
  29: rustc_interface::interface::run_compiler_in_existing_thread_pool
  30: std::thread::local::LocalKey<T>::with
  31: scoped_tls::ScopedKey<T>::set
  32: syntax::with_globals

[jonas-schievink]

Possible duplicate of #66065, please check whether this occurs on the newest nightly as well

[danw8]

This is fixed in the #66065