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Rollup merge of #131381 - Nadrieril:min-match-ergonomics, r=pnkfelix

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Implement edition 2024 match ergonomics restrictions

This implements the minimalest version of [match ergonomics for edition 2024](https://rust-lang.github.io/rfcs/3627-match-ergonomics-2024.html). This minimal version makes it an error to ever reset the default binding mode. The implemented proposal is described precisely [here](https://hackmd.io/zUqs2ISNQ0Wrnxsa9nhD0Q#RFC-3627-nano), where it is called "RFC 3627-nano".

Rules:
- Rule 1C: When the DBM (default binding mode) is not `move` (whether or not behind a reference), writing `mut`, `ref`, or `ref mut` on a binding is an error.
- Rule 2C: Reference patterns can only match against references in the scrutinee when the DBM is `move`.

This minimal version is forward-compatible with the main proposals for match ergonomics 2024: [RFC3627](https://rust-lang.github.io/rfcs/3627-match-ergonomics-2024.html) itself, the alternative [rule 4-early variant](https://rust-lang.github.io/rfcs/3627-match-ergonomics-2024.html), and [others](https://hackmd.io/zUqs2ISNQ0Wrnxsa9nhD0Q). The idea is to give us more time to iron out a final proposal.

This includes a migration lint that desugars any offending pattern into one that doesn't make use of match ergonomics. Such patterns have identical meaning across editions.

This PR insta-stabilizes the proposed behavior onto edition 2024.

r? `@ghost`

Tracking:

- https://github.com/rust-lang/rust/issues/123076
This commit is contained in:
Matthias Krüger 2024-10-16 19:18:30 +02:00 • committed by GitHub
commit c1ed1f133e
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17 changed files with 757 additions and 242 deletions
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15
compiler/rustc_middle/src/ty/typeck_results.rs
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@ -73,9 +73,10 @@ pub struct TypeckResults<'tcx> {
/// Stores the actual binding mode for all instances of [`BindingMode`].
pat_binding_modes: ItemLocalMap<BindingMode>,
/// Top-level patterns whose match ergonomics need to be desugared
/// by the Rust 2021 -> 2024 migration lint.
rust_2024_migration_desugared_pats: ItemLocalSet,
/// Top-level patterns whose match ergonomics need to be desugared by the Rust 2021 -> 2024
/// migration lint. The boolean indicates whether the emitted diagnostic should be a hard error
/// (if any of the incompatible pattern elements are in edition 2024).
rust_2024_migration_desugared_pats: ItemLocalMap<bool>,
/// Stores the types which were implicitly dereferenced in pattern binding modes
/// for later usage in THIR lowering. For example,
@ -418,15 +419,15 @@ impl<'tcx> TypeckResults<'tcx> {
LocalTableInContextMut { hir_owner: self.hir_owner, data: &mut self.pat_adjustments }
}
pub fn rust_2024_migration_desugared_pats(&self) -> LocalSetInContext<'_> {
LocalSetInContext {
pub fn rust_2024_migration_desugared_pats(&self) -> LocalTableInContext<'_, bool> {
LocalTableInContext {
hir_owner: self.hir_owner,
data: &self.rust_2024_migration_desugared_pats,
}
}
pub fn rust_2024_migration_desugared_pats_mut(&mut self) -> LocalSetInContextMut<'_> {
LocalSetInContextMut {
pub fn rust_2024_migration_desugared_pats_mut(&mut self) -> LocalTableInContextMut<'_, bool> {
LocalTableInContextMut {
hir_owner: self.hir_owner,
data: &mut self.rust_2024_migration_desugared_pats,
}