Rollup merge of #77587 - ehuss:unicode-escape-span, r=ecstatic-morse

Fix span for unicode escape suggestion. If a unicode escape is missing the curly braces, the suggested fix is to add the curly braces, but the span for the fix was incorrect. It was not covering the `\u`, but the suggested text includes the `\u`, causing the resulting fix to be `"\u\u{1234}"`. This changes it so that the span includes the `\u`. An alternate fix would be to remove `\u` from the suggested fix, but I think the error message reads better if the entire escape is included.

Author: jonas-schievink

compiler/rustc_parse/src/lexer/unescape_error_reporting.rs

@@ -181,10 +181,9 @@ pub(crate) fn emit_unescape_error(
 
  if suggestion_len > 0 {
  suggestion.push('}');
- let lo = char_span.lo();
- let hi = lo + BytePos(suggestion_len as u32);
+ let hi = char_span.lo() + BytePos(suggestion_len as u32);
  diag.span_suggestion(
- span.with_lo(lo).with_hi(hi),
+ span.with_hi(hi),
  "format of unicode escape sequences uses braces",
  suggestion,
  Applicability::MaybeIncorrect,

src/test/ui/fmt/format-string-error-2.stderr

@@ -2,9 +2,7 @@ error: incorrect unicode escape sequence
  --> $DIR/format-string-error-2.rs:77:20
  |
 LL | println!("\x7B}\u8 {", 1);
- | ^^-
- | |
- | help: format of unicode escape sequences uses braces: `\u{8}`
+ | ^^^ help: format of unicode escape sequences uses braces: `\u{8}`
 
 error: invalid format string: expected `'}'`, found `'a'`
  --> $DIR/format-string-error-2.rs:5:5

src/test/ui/parser/issue-23620-invalid-escapes.stderr

@@ -80,9 +80,9 @@ error: incorrect unicode escape sequence
  --> $DIR/issue-23620-invalid-escapes.rs:32:14
  |
 LL | let _ = "\u8f";
- | ^^--
- |  |
- |  help: format of unicode escape sequences uses braces: `\u{8f}`
+ | ^^^-
+ | |
+ | help: format of unicode escape sequences uses braces: `\u{8f}`
 
 error: aborting due to 13 previous errors