Rustc ICE while formatting

[ThatGeoGuy]

I'm not sure what to add here, but all I ran was cargo +nightly fmt --check -p <my-crate> and got some kind of internal compiler error.

My Rustfmt.toml is:

edition = "2021"
style_edition = "2021"
error_on_line_overflow = true
error_on_unformatted = true

and the backtrace is:

rustc-ice-2026-03-30T22_31_13-4055538.txt

I'm not sure why this happening, but I felt I should offer the backtrace!

[ytmimi]

@ThatGeoGuy please put together a minimal reproduction that the team or a contributor can use to verify the issue.

[jieyouxu]

There's a unicode multi-byte ellipses … (probably U+2026) somewhere

end byte index 100 is not a char boundary; it is inside '…' (bytes 98..101 of string)

But yeah this needs a repro to double-check, even if this is likely a duplicate of another codepoint-boundary-related issue

[jieyouxu]

Maybe this is something like #6850? Where you happen to have a multi-byte unicode character inside a long string literal just in the middle of max width.