assertion failed: bpos.to_u32() >= mbc.pos.to_u32() + mbc.bytes as u32

[dwrensha]

rustc crashes on the following input, found by fuzz_rustc:

fn i(){println!("🦀%%%";r

error: this file contains an unclosed delimiter
 --> bug.rs:1:25
  |
1 | fn i(){println!("🦀%%%";r
  |       -        -         ^
  |       |        |
  |       |        unclosed delimiter
  |       unclosed delimiter

error: expected `,`, found `;`
 --> bug.rs:1:23
  |
1 | fn i(){println!("🦀%%%";r
  |                        ^ expected `,`

error: argument never used
 --> bug.rs:1:24
  |
1 | fn i(){println!("🦀%%%";r
  |                         ^ argument never used
  |
thread 'rustc' panicked at 'assertion failed: bpos.to_u32() >= mbc.pos.to_u32() + mbc.bytes as u32', compiler/rustc_span/src/lib.rs:1710:17
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/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.59.0-nightly (c09a9529c 2021-12-23) running on x86_64-unknown-linux-gnu

[dwrensha]

searched nightlies: from nightly-2021-01-01 to nightly-2021-12-24
regressed nightly: nightly-2021-10-02
searched commits: from aa7aca3 to c02371c
regressed commit: b6057bf

bisected with cargo-bisect-rustc v0.6.0

Host triple: x86_64-unknown-linux-gnu
Reproduce with:

cargo bisect-rustc --start=2021-1-1 --end=2021-12-24 --regress ice 

[dwrensha]

The regression happened in #89340. cc @FabianWolff.

[BGR360]

@rustbot label regression-from-stable-to-stable

[apiraino]

Assigning priority as discussed in the Zulip thread of the Prioritization Working Group.

@rustbot label -I-prioritize +P-low

[inquisitivecrystal]

I've been taking a look at this. It's pretty interesting. I'm not entirely sure I'll be able to work it out, but I figure I may as well assign myself for the time being while I attempt to solve it.

[Badel2]

Another test case:

fn f(){(print!(á