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Merged
merged 4 commits into from
Jun 6, 2024
Merged

Match ergonomics 2024: align implementation with RFC #125168

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a32fb2f
Remove `ref_pat_everywhere`
Jules-Bertholet May 15, 2024
eb91f3b
`&mut` no longer peels off `&`
Jules-Bertholet May 15, 2024
0746577
Gate implicit mutable by-reference bindings behind `mut ref`
Jules-Bertholet May 15, 2024
af75014
"No `ref mut` behind `&`" on all editions
Jules-Bertholet May 15, 2024
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3 changes: 3 additions & 0 deletions compiler/rustc_feature/src/removed.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -128,6 +128,8 @@ declare_features! (
/// Allows the use of type alias impl trait in function return positions
(removed, min_type_alias_impl_trait, "1.56.0", Some(63063),
Some("removed in favor of full type_alias_impl_trait")),
/// Make `mut` not reset the binding mode on edition >= 2024.
(removed, mut_preserve_binding_mode_2024, "1.79.0", Some(123076), Some("superseded by `ref_pat_eat_one_layer_2024`")),
(removed, needs_allocator, "1.4.0", Some(27389),
Some("subsumed by `#![feature(allocator_internals)]`")),
/// Allows use of unary negate on unsigned integers, e.g., -e for e: u8
Expand Down Expand Up @@ -181,6 +183,7 @@ declare_features! (
(removed, pushpop_unsafe, "1.2.0", None, None),
(removed, quad_precision_float, "1.0.0", None, None),
(removed, quote, "1.33.0", Some(29601), None),
(removed, ref_pat_everywhere, "1.79.0", Some(123076), Some("superseded by `ref_pat_eat_one_layer_2024")),
(removed, reflect, "1.0.0", Some(27749), None),
/// Allows using the `#[register_attr]` attribute.
(removed, register_attr, "1.65.0", Some(66080),
Expand Down
4 changes: 0 additions & 4 deletions compiler/rustc_feature/src/unstable.rs
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Expand Up @@ -527,8 +527,6 @@ declare_features! (
(unstable, more_qualified_paths, "1.54.0", Some(86935)),
/// Allows the `#[must_not_suspend]` attribute.
(unstable, must_not_suspend, "1.57.0", Some(83310)),
/// Make `mut` not reset the binding mode on edition >= 2024.
(incomplete, mut_preserve_binding_mode_2024, "1.79.0", Some(123076)),
/// Allows `mut ref` and `mut ref mut` identifier patterns.
(incomplete, mut_ref, "1.79.0", Some(123076)),
/// Allows using `#[naked]` on functions.
Expand Down Expand Up @@ -571,8 +569,6 @@ declare_features! (
(unstable, raw_ref_op, "1.41.0", Some(64490)),
/// Makes `&` and `&mut` patterns eat only one layer of references in Rust 2024.
(incomplete, ref_pat_eat_one_layer_2024, "1.79.0", Some(123076)),
/// Allows `&` and `&mut` patterns to consume match-ergonomics-inserted references.
(incomplete, ref_pat_everywhere, "1.79.0", Some(123076)),
/// Allows using the `#[register_tool]` attribute.
(unstable, register_tool, "1.41.0", Some(66079)),
/// Allows the `#[repr(i128)]` attribute for enums.
Expand Down
156 changes: 66 additions & 90 deletions compiler/rustc_hir_typeck/src/pat.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -12,7 +12,7 @@ use rustc_infer::infer;
use rustc_middle::mir::interpret::ErrorHandled;
use rustc_middle::ty::{self, Ty, TypeVisitableExt};
use rustc_middle::{bug, span_bug};
use rustc_session::lint::builtin::NON_EXHAUSTIVE_OMITTED_PATTERNS;
use rustc_session::{lint::builtin::NON_EXHAUSTIVE_OMITTED_PATTERNS, parse::feature_err};
use rustc_span::edit_distance::find_best_match_for_name;
use rustc_span::hygiene::DesugaringKind;
use rustc_span::source_map::Spanned;
Expand Down Expand Up @@ -335,9 +335,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
match adjust_mode {
AdjustMode::Pass => (expected, def_br, max_ref_mutbl),
AdjustMode::Reset => (expected, ByRef::No, MutblCap::Mut),
AdjustMode::Peel => {
self.peel_off_references(pat, expected, def_br, Mutability::Mut, max_ref_mutbl)
}
AdjustMode::Peel => self.peel_off_references(pat, expected, def_br, max_ref_mutbl),
}
}

Expand Down Expand Up @@ -408,8 +406,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
pat: &'tcx Pat<'tcx>,
expected: Ty<'tcx>,
mut def_br: ByRef,
max_peelable_mutability: Mutability,
mut max_ref_mutability: MutblCap,
mut max_ref_mutbl: MutblCap,
) -> (Ty<'tcx>, ByRef, MutblCap) {
let mut expected = self.try_structurally_resolve_type(pat.span, expected);
// Peel off as many `&` or `&mut` from the scrutinee type as possible. For example,
Expand All @@ -421,9 +418,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
//
// See the examples in `ui/match-defbm*.rs`.
let mut pat_adjustments = vec![];
while let ty::Ref(_, inner_ty, inner_mutability) = *expected.kind()
&& inner_mutability <= max_peelable_mutability
{
while let ty::Ref(_, inner_ty, inner_mutability) = *expected.kind() {
debug!("inspecting {:?}", expected);

debug!("current discriminant is Ref, inserting implicit deref");
Expand All @@ -443,10 +438,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
});
}

if pat.span.at_least_rust_2024() && self.tcx.features().ref_pat_eat_one_layer_2024 {
def_br = def_br.cap_ref_mutability(max_ref_mutability.as_mutbl());
if self.tcx.features().ref_pat_eat_one_layer_2024 {
def_br = def_br.cap_ref_mutability(max_ref_mutbl.as_mutbl());
if def_br == ByRef::Yes(Mutability::Not) {
max_ref_mutability = MutblCap::Not;
max_ref_mutbl = MutblCap::Not;
}
}

Expand All @@ -458,7 +453,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
.insert(pat.hir_id, pat_adjustments);
}

(expected, def_br, max_ref_mutability)
(expected, def_br, max_ref_mutbl)
}

fn check_pat_lit(
Expand Down Expand Up @@ -674,17 +669,27 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {

// Determine the binding mode...
let bm = match user_bind_annot {
// `mut` resets binding mode on edition <= 2021
BindingMode(ByRef::No, Mutability::Mut)
if !(pat.span.at_least_rust_2024()
&& self.tcx.features().mut_preserve_binding_mode_2024)
&& matches!(def_br, ByRef::Yes(_)) =>
{
self.typeck_results
.borrow_mut()
.rust_2024_migration_desugared_pats_mut()
.insert(pat_info.top_info.hir_id);
BindingMode(ByRef::No, Mutability::Mut)
BindingMode(ByRef::No, Mutability::Mut) if matches!(def_br, ByRef::Yes(_)) => {
if pat.span.at_least_rust_2024() && self.tcx.features().ref_pat_eat_one_layer_2024 {
if !self.tcx.features().mut_ref {
feature_err(
&self.tcx.sess,
sym::mut_ref,
pat.span.until(ident.span),
"binding cannot be both mutable and by-reference",
)
.emit();
}

BindingMode(def_br, Mutability::Mut)
} else {
// `mut` resets binding mode on edition <= 2021
self.typeck_results
.borrow_mut()
.rust_2024_migration_desugared_pats_mut()
.insert(pat_info.top_info.hir_id);
BindingMode(ByRef::No, Mutability::Mut)
}
}
BindingMode(ByRef::No, mutbl) => BindingMode(def_br, mutbl),
BindingMode(ByRef::Yes(_), _) => user_bind_annot,
Expand Down Expand Up @@ -2125,57 +2130,47 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
mut expected: Ty<'tcx>,
mut pat_info: PatInfo<'tcx, '_>,
) -> Ty<'tcx> {
// FIXME: repace with `bool` once final decision on 1 vs 2 layers is made
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
enum MatchErgonomicsMode {
EatOneLayer,
EatTwoLayers,
Legacy,
}
let no_ref_mut_behind_and = self.tcx.features().ref_pat_eat_one_layer_2024;
let new_match_ergonomics = pat.span.at_least_rust_2024() && no_ref_mut_behind_and;

let match_ergonomics_mode =
if pat.span.at_least_rust_2024() && self.tcx.features().ref_pat_eat_one_layer_2024 {
MatchErgonomicsMode::EatOneLayer
} else if self.tcx.features().ref_pat_everywhere {
MatchErgonomicsMode::EatTwoLayers
} else {
MatchErgonomicsMode::Legacy
};
let pat_prefix_span =
inner.span.find_ancestor_inside(pat.span).map(|end| pat.span.until(end));

let mut inherited_ref_mutbl_match = false;
if match_ergonomics_mode != MatchErgonomicsMode::Legacy {
if no_ref_mut_behind_and {
if pat_mutbl == Mutability::Not {
// Prevent the inner pattern from binding with `ref mut`.
pat_info.max_ref_mutbl = pat_info.max_ref_mutbl.cap_to_weakly_not(
inner.span.find_ancestor_inside(pat.span).map(|end| pat.span.until(end)),
);
pat_info.max_ref_mutbl = pat_info.max_ref_mutbl.cap_to_weakly_not(pat_prefix_span);
}
} else {
pat_info.max_ref_mutbl = MutblCap::Mut;
}

if new_match_ergonomics {
if let ByRef::Yes(inh_mut) = pat_info.binding_mode {
inherited_ref_mutbl_match = pat_mutbl <= inh_mut;
}
// ref pattern consumes inherited reference

if pat_mutbl > inh_mut {
// Tried to match inherited `ref` with `&mut`, which is an error
let err_msg = "cannot match inherited `&` with `&mut` pattern";
let err = if let Some(span) = pat_prefix_span {
let mut err = self.dcx().struct_span_err(span, err_msg);
err.span_suggestion_verbose(
span,
"replace this `&mut` pattern with `&`",
"&",
Applicability::MachineApplicable,
);
err
} else {
self.dcx().struct_span_err(pat.span, err_msg)
};
err.emit();
}

if inherited_ref_mutbl_match {
pat_info.binding_mode = ByRef::No;
if match_ergonomics_mode == MatchErgonomicsMode::EatOneLayer {
self.typeck_results.borrow_mut().skipped_ref_pats_mut().insert(pat.hir_id);
self.check_pat(inner, expected, pat_info);
return expected;
}
} else if match_ergonomics_mode == MatchErgonomicsMode::EatOneLayer
&& pat_mutbl == Mutability::Mut
{
// `&mut` patterns pell off `&` references
let (new_expected, new_bm, max_ref_mutbl) = self.peel_off_references(
pat,
expected,
pat_info.binding_mode,
Mutability::Not,
pat_info.max_ref_mutbl,
);
expected = new_expected;
pat_info.binding_mode = new_bm;
pat_info.max_ref_mutbl = max_ref_mutbl;
self.typeck_results.borrow_mut().skipped_ref_pats_mut().insert(pat.hir_id);
self.check_pat(inner, expected, pat_info);
return expected;
}
} else {
// Reset binding mode on old editions
Expand All @@ -2188,8 +2183,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
.rust_2024_migration_desugared_pats_mut()
.insert(pat_info.top_info.hir_id);
}

pat_info.max_ref_mutbl = MutblCap::Mut;
}

let tcx = self.tcx;
Expand All @@ -2204,34 +2197,17 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
// the bad interactions of the given hack detailed in (note_1).
debug!("check_pat_ref: expected={:?}", expected);
match *expected.kind() {
ty::Ref(_, r_ty, r_mutbl) if r_mutbl == pat_mutbl => {
if r_mutbl == Mutability::Not
&& match_ergonomics_mode != MatchErgonomicsMode::Legacy
{
ty::Ref(_, r_ty, r_mutbl)
if (new_match_ergonomics && r_mutbl >= pat_mutbl)
|| r_mutbl == pat_mutbl =>
{
if no_ref_mut_behind_and && r_mutbl == Mutability::Not {
pat_info.max_ref_mutbl = MutblCap::Not;
}

(expected, r_ty)
}

// `&` pattern eats `&mut` reference
ty::Ref(_, r_ty, Mutability::Mut)
if pat_mutbl == Mutability::Not
&& match_ergonomics_mode != MatchErgonomicsMode::Legacy =>
{
(expected, r_ty)
}

_ if inherited_ref_mutbl_match
&& match_ergonomics_mode == MatchErgonomicsMode::EatTwoLayers =>
{
// We already matched against a match-ergonmics inserted reference,
// so we don't need to match against a reference from the original type.
// Save this info for use in lowering later
self.typeck_results.borrow_mut().skipped_ref_pats_mut().insert(pat.hir_id);
(expected, expected)
}

_ => {
let inner_ty = self.next_ty_var(inner.span);
let ref_ty = self.new_ref_ty(pat.span, pat_mutbl, inner_ty);
Expand Down
14 changes: 0 additions & 14 deletions tests/ui/feature-gates/feature-gate-ref_pat_everywhere.rs
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49 changes: 0 additions & 49 deletions tests/ui/feature-gates/feature-gate-ref_pat_everywhere.stderr
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15 changes: 0 additions & 15 deletions tests/ui/match/ref_pat_eat_one_layer_2024/ref_pat_eat_one_layer_2024.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -23,9 +23,6 @@ pub fn main() {
if let Some(Some(&x)) = &Some(&Some(0)) {
let _: u32 = x;
}
if let Some(&mut Some(&x)) = &Some(&mut Some(0)) {
let _: u32 = x;
}
if let Some(&Some(&x)) = &mut Some(&Some(0)) {
let _: u32 = x;
}
Expand All @@ -35,9 +32,6 @@ pub fn main() {
if let Some(&Some(&mut ref x)) = Some(&Some(&mut 0)) {
let _: &u32 = x;
}
if let Some(Some(&mut x)) = &Some(Some(&mut 0)) {
let _: &u32 = x;
}
if let &Some(Some(x)) = &Some(&mut Some(0)) {
let _: &u32 = x;
}
Expand All @@ -59,13 +53,4 @@ pub fn main() {
if let Some(&Some(x)) = &mut Some(Some(0)) {
let _: u32 = x;
}

let &mut x = &&mut 0;
let _: &u32 = x;

let &mut x = &&&&&&&&&&&&&&&&&&&&&&&&&&&&mut 0;
let _: &u32 = x;

let &mut &mut &mut &mut x = &mut &&&&mut &&&mut &mut 0;
let _: &u32 = x;
}
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