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//! Migration code for the `expr_fragment_specifier_2024` rule.
use rustc_ast::token::{Token, TokenKind};
use rustc_ast::tokenstream::{TokenStream, TokenTree};
use rustc_session::lint::FutureIncompatibilityReason;
use rustc_session::{declare_lint, declare_lint_pass};
use rustc_span::edition::Edition;
use rustc_span::sym;
use tracing::debug;
use crate::lints::MacroExprFragment2024;
use crate::EarlyLintPass;
declare_lint! {
/// The `edition_2024_expr_fragment_specifier` lint detects the use of
/// `expr` fragments in macros during migration to the 2024 edition.
///
/// The `expr` fragment specifier will accept more expressions in the 2024
/// edition. To maintain the behavior from the 2021 edition and earlier, use
/// the `expr_2021` fragment specifier.
///
/// ### Example
///
/// ```rust,edition2021,compile_fail
/// #![deny(edition_2024_expr_fragment_specifier)]
/// macro_rules! m {
/// ($e:expr) => {
/// $e
/// }
/// }
///
/// fn main() {
/// m!(1);
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Rust [editions] allow the language to evolve without breaking backwards
/// compatibility. This lint catches code that uses [macro matcher fragment
/// specifiers] that have changed meaning in the 2024 edition. If you switch
/// to the new edition without updating the code, your macros may behave
/// differently.
///
/// In the 2024 edition, the `expr` fragment specifier `expr` will also
/// match `const { ... }` blocks. This means if a macro had a pattern that
/// matched `$e:expr` and another that matches `const { $e: expr }`, for
/// example, that under the 2024 edition the first pattern would match while
/// in the 2021 and earlier editions the second pattern would match. To keep
/// the old behavior, use the `expr_2021` fragment specifier.
///
/// This lint detects macros whose behavior might change due to the changing
/// meaning of the `expr` fragment specifier. 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. This provides a
/// completely automated way to update old code for a new edition.
///
/// Using `cargo fix --edition` with this lint will ensure that your code
/// retains the same behavior. This may not be the desired, as macro authors
/// often will want their macros to use the latest grammar for matching
/// expressions. Be sure to carefully review changes introduced by this lint
/// to ensure the macros implement the desired behavior.
///
/// [editions]: https://doc.rust-lang.org/edition-guide/
/// [macro matcher fragment specifiers]: https://doc.rust-lang.org/nightly/edition-guide/rust-2024/macro-fragment-specifiers.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 behavior, use the `expr_2021` fragment specifier.",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::EditionSemanticsChange(Edition::Edition2024),
reference: "Migration Guide <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/macro-fragment-specifiers.html>",
};
}
declare_lint_pass!(Expr2024 => [EDITION_2024_EXPR_FRAGMENT_SPECIFIER,]);
impl Expr2024 {
fn check_tokens(&mut self, cx: &crate::EarlyContext<'_>, tokens: &TokenStream) {
let mut prev_colon = false;
let mut prev_identifier = false;
let mut prev_dollar = false;
for tt in tokens.trees() {
debug!(
"check_tokens: {:?} - colon {prev_dollar} - ident {prev_identifier} - colon {prev_colon}",
tt
);
match tt {
TokenTree::Token(token, _) => match token.kind {
TokenKind::Dollar => {
prev_dollar = true;
continue;
}
TokenKind::Ident(..) | TokenKind::NtIdent(..) => {
if prev_colon && prev_identifier && prev_dollar {
self.check_ident_token(cx, token);
} else if prev_dollar {
prev_identifier = true;
continue;
}
}
TokenKind::Colon => {
if prev_dollar && prev_identifier {
prev_colon = true;
continue;
}
}
_ => {}
},
TokenTree::Delimited(.., tts) => self.check_tokens(cx, tts),
}
prev_colon = false;
prev_identifier = false;
prev_dollar = false;
}
}
fn check_ident_token(&mut self, cx: &crate::EarlyContext<'_>, token: &Token) {
debug!("check_ident_token: {:?}", token);
let (sym, edition) = match token.kind {
TokenKind::Ident(sym, _) => (sym, Edition::Edition2024),
_ => return,
};
debug!("token.span.edition(): {:?}", token.span.edition());
if token.span.edition() >= edition {
return;
}
if sym != sym::expr {
return;
}
debug!("emitting lint");
cx.builder.emit_span_lint(
&EDITION_2024_EXPR_FRAGMENT_SPECIFIER,
token.span.into(),
MacroExprFragment2024 { suggestion: token.span },
);
}
}
impl EarlyLintPass for Expr2024 {
fn check_mac_def(&mut self, cx: &crate::EarlyContext<'_>, mc: &rustc_ast::MacroDef) {
self.check_tokens(cx, &mc.body.tokens);
}
}