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

[dwrensha]

$ echo -n 'fn f(){(print!(á' > bug.rs
$ rustc bug.rs
error: this file contains an unclosed delimiter
 --> bug.rs:1:17
  |
1 | fn f(){(print!(á
  |       --      - ^
  |       ||      |
  |       ||      unclosed delimiter
  |       |unclosed delimiter
  |       unclosed delimiter

error: format argument must be a string literal
 --> bug.rs:1:16
  |
1 | fn f(){(print!(á
  |                ^
  |
help: you might be missing a string literal to format with
  |
1 | fn f(){(print!("{}", á
  |                +++++

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 (83b15bfe1 2021-12-28) running on x86_64-unknown-linux-gnu

query stack during panic:
end of query stack
error: aborting due to 2 previous errors

Reported by @Badel2 here: #92267 (comment)
(Note that #92460 fixes #92267, but does not fix this bug.)

[dwrensha]

searched nightlies: from nightly-2021-01-07 to nightly-2021-12-24
regressed nightly: nightly-2021-09-12
searched commits: from b69fe57 to 8c2b6ea
regressed commit: 43769af

bisected with cargo-bisect-rustc v0.6.0

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

cargo bisect-rustc --start=2021-1-7 --end=2021-12-24 --regress ice 

[dwrensha]

This regression was introduced in #88779. cc @estebank

[dwrensha]

Not a fix, but if I make this change

diff --git a/compiler/rustc_lint/src/unused.rs b/compiler/rustc_lint/src/unused.rs
index 755e24d5413..a74a83567a3 100644
--- a/compiler/rustc_lint/src/unused.rs
+++ b/compiler/rustc_lint/src/unused.rs
@@ -512,7 +512,7 @@ fn emit_unused_delims_expr(
                 if value.span.from_expansion() || expr.span.from_expansion() {
                     (
                         value.span.with_hi(value.span.lo() + BytePos(1)),
-                        value.span.with_lo(value.span.hi() - BytePos(1)),
+                        value.span.with_lo(value.span.hi()),
                     )
                 } else {
                     (value.span.with_hi(expr.span.lo()), value.span.with_lo(expr.span.hi()))

then there is no longer an ICE and I get

error: this file contains an unclosed delimiter
 --> /home/dwrensha/Desktop/bug.rs:1:17
  |
1 | fn f(){(print!(á
  |       --      - ^
  |       ||      |
  |       ||      unclosed delimiter
  |       |unclosed delimiter
  |       unclosed delimiter

error: format argument must be a string literal
 --> /home/dwrensha/Desktop/bug.rs:1:16
  |
1 | fn f(){(print!(á
  |                ^
  |
help: you might be missing a string literal to format with
  |
1 | fn f(){(print!("{}", á
  |                +++++

warning: unnecessary parentheses around block return value
 --> /home/dwrensha/Desktop/bug.rs:1:8
  |
1 | fn f(){(print!(á
  |        ^        ^
  |
  = note: `#[warn(unused_parens)]` on by default
help: remove these parentheses
  |
1 - fn f(){(print!(á
1 + fn f(){print!(á
  | 

error: aborting due to 2 previous errors; 1 warning emitted

[Badel2]

Thanks for opening the issue @dwrensha.

If someone finds a fix but doesn't know how to add the test, this pull request which solves a similar ICE has an example of how to add a test when there is a missing newline:

#91273