Rollup merge of #108523 - TaKO8Ki:avoid-str-to-string-conversions, r=…

…Nilstrieb

Avoid `&str` to `String` conversions

This patch removes some unnecessary `&str` to `String` conversions.

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -386,7 +386,7 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
  ).span_suggestion_verbose(
  lhs.span.shrink_to_lo(),
  "you might have meant to introduce a new binding",
- "let ".to_string(),
+ "let ",
  Applicability::MachineApplicable,
  ).emit();
  }

compiler/rustc_borrowck/src/diagnostics/move_errors.rs

@@ -467,7 +467,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
  err.span_suggestion_verbose(
  span.shrink_to_lo(),
  "consider borrowing here",
- "&".to_string(),
+ '&',
  Applicability::MaybeIncorrect,
  );
  }

compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs

@@ -385,7 +385,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
  err.span_suggestion_verbose(
  local_decl.source_info.span.shrink_to_lo(),
  "consider changing this to be mutable",
- "mut ".to_string(),
+ "mut ",
  Applicability::MachineApplicable,
  );
  let tcx = self.infcx.tcx;