Rollup merge of #86104 - FabianWolff:issue-86085, r=davidtwco

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.

0 files changed, 0 insertions, 0 deletions