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4ff55ecf04
Fix span calculation in format strings This pull request fixes #86085. The ICE described there is due to an error in the span calculation inside format strings, if the format string is the result of a macro invocation: ```rust fn main() { format!(concat!("abc}")); } ``` currently produces: ``` error: invalid format string: unmatched `}` found --> test.rs:2:17 | 2 | format!(concat!("abc}")); | ^ unmatched `}` in format string ``` which is obviously incorrect. This happens because the span of the entire `concat!()` is combined with the _relative_ location of the unmatched `` `}` `` in the _result_ of the macro invocation (i.e. 4). In #86085, this has led to a span that starts or ends in the middle of a multibyte character, but the root cause was the same. This pull request fixes the problem.