fixup! Adds expr_2024 migration lit

Signed-off-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com>

compiler/rustc_lint/src/lints.rs

@@ -325,7 +325,7 @@ pub struct BuiltinTypeAliasGenericBounds<'a, 'b> {
 
 #[derive(LintDiagnostic)]
 #[diag(lint_macro_expr_fragment_specifier_2024_migration)]
-pub struct MacroExprFragment2023 {
+pub struct MacroExprFragment2024 {
  #[suggestion(code = "expr_2021", applicability = "machine-applicable")]
  pub suggestion: Span,
 }

compiler/rustc_lint/src/macro_expr_fragment_specifier_2024_migration.rs

@@ -12,14 +12,38 @@ use rustc_session::lint::FutureIncompatibilityReason;
 use rustc_span::edition::Edition;
 use rustc_span::sym;
 
-use crate::lints::MacroExprFragment2023;
+use crate::lints::MacroExprFragment2024;
 use crate::EarlyLintPass;
 
 declare_lint! {
+ /// TODO: better explaination for this.
+ ///
+ /// ### Explanation
+ ///
+ /// Rust [editions] allow the language to evolve without breaking
+ /// backwards compatibility. This lint catches code that uses new keywords
+ /// that are added to the language that are used as identifiers (such as a
+ /// variable name, function name, etc.). If you switch the compiler to a
+ /// new edition without updating the code, then it will fail to compile if
+ /// you are using a new keyword as an identifier.
+ ///
+ /// FIXME: change this: You can manually change the identifiers from `expr` to `expr2021`,
+ /// or use a [raw identifier], for example `r#gen`, to transition to a new edition.
+ ///
+ /// This lint solves the problem automatically. It is "allow" by default
+ /// because the code is perfectly valid in older editions. The [`cargo
+ /// fix`] tool with the `--edition` flag will switch this lint to "warn"
+ /// and automatically apply the suggested fix from the compiler (which is
+ /// to use a raw identifier). This provides a completely automated way to
+ /// update old code for a new edition.
+ ///
+ /// [editions]: https://doc.rust-lang.org/edition-guide/
+ /// [raw identifier]: https://doc.rust-lang.org/reference/identifiers.html
+ /// [`cargo fix`]: https://doc.rust-lang.org/cargo/commands/cargo-fix.html
  pub EDITION_2024_EXPR_FRAGMENT_SPECIFIER,
  Allow,
  "The `expr` fragment specifier will accept more expressions in the 2024 edition. \
- To keep the existing before, use the `expr_2021` fragment specifier.",
+ To keep the existing behavior, use the `expr_2021` fragment specifier.",
  @future_incompatible = FutureIncompatibleInfo {
  reason: FutureIncompatibilityReason::EditionSemanticsChange(Edition::Edition2024),
  reference: "issue #123742 <https://github.com/rust-lang/rust/issues/123742>",
@@ -30,11 +54,9 @@ declare_lint_pass!(Expr2024 => [EDITION_2024_EXPR_FRAGMENT_SPECIFIER,]);
 
 impl Expr2024 {
  fn check_tokens(&mut self, cx: &crate::EarlyContext<'_>, tokens: &TokenStream) {
- // Check if the preceding token is `$`, because we want to allow `$async`, etc.
  let mut prev_dollar = false;
  for tt in tokens.trees() {
  match tt {
- // Only report non-raw idents.
  TokenTree::Token(token, _) => {
  if token.kind == TokenKind::Dollar {
  prev_dollar = true;
@@ -71,7 +93,7 @@ impl Expr2024 {
  cx.builder.emit_span_lint(
  &EDITION_2024_EXPR_FRAGMENT_SPECIFIER,
  token.span.into(),
- MacroExprFragment2023 { suggestion: token.span },
+ MacroExprFragment2024 { suggestion: token.span },
  );
  }
 }