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NadrierilNadrieril
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Reveal opaque types in exhaustiveness checking
1 parent 7e4924b commit 2a87bae

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7 files changed

+76
-42
lines changed

7 files changed

+76
-42
lines changed

‎compiler/rustc_mir_build/src/thir/pattern/check_match.rs

+4
Original file line numberDiff line numberDiff line change
@@ -28,13 +28,15 @@ use rustc_span::hygiene::DesugaringKind;
2828
use rustc_span::Span;
2929

3030
pub(crate) fn check_match(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Result<(), ErrorGuaranteed> {
31+
let typeck_results = tcx.typeck(def_id);
3132
let (thir, expr) = tcx.thir_body(def_id)?;
3233
let thir = thir.borrow();
3334
let pattern_arena = TypedArena::default();
3435
let dropless_arena = DroplessArena::default();
3536
let mut visitor = MatchVisitor {
3637
tcx,
3738
thir: &*thir,
39+
typeck_results,
3840
param_env: tcx.param_env(def_id),
3941
lint_level: tcx.local_def_id_to_hir_id(def_id),
4042
let_source: LetSource::None,
@@ -80,6 +82,7 @@ enum LetSource {
8082
struct MatchVisitor<'thir, 'p, 'tcx> {
8183
tcx: TyCtxt<'tcx>,
8284
param_env: ty::ParamEnv<'tcx>,
85+
typeck_results: &'tcx ty::TypeckResults<'tcx>,
8386
thir: &'thir Thir<'tcx>,
8487
lint_level: HirId,
8588
let_source: LetSource,
@@ -382,6 +385,7 @@ impl<'thir, 'p, 'tcx> MatchVisitor<'thir, 'p, 'tcx> {
382385
scrutinee.map(|scrut| self.is_known_valid_scrutinee(scrut)).unwrap_or(true);
383386
MatchCheckCtxt {
384387
tcx: self.tcx,
388+
typeck_results: self.typeck_results,
385389
param_env: self.param_env,
386390
module: self.tcx.parent_module(self.lint_level).to_def_id(),
387391
pattern_arena: self.pattern_arena,

‎compiler/rustc_pattern_analysis/src/lib.rs

+2-1
Original file line numberDiff line numberDiff line change
@@ -62,7 +62,8 @@ pub trait TypeCx: Sized + Clone + fmt::Debug {
6262
/// patterns during analysis.
6363
type PatData: Clone + Default;
6464

65-
fn is_opaque_ty(ty: Self::Ty) -> bool;
65+
/// FIXME(Nadrieril): `Cx` should only give us revealed types.
66+
fn reveal_opaque_ty(&self, ty: Self::Ty) -> Self::Ty;
6667
fn is_exhaustive_patterns_feature_on(&self) -> bool;
6768

6869
/// The number of fields for this constructor.

‎compiler/rustc_pattern_analysis/src/lints.rs

+7-15
Original file line numberDiff line numberDiff line change
@@ -48,22 +48,14 @@ impl<'a, 'p, 'tcx> PatternColumn<'a, 'p, 'tcx> {
4848
fn is_empty(&self) -> bool {
4949
self.patterns.is_empty()
5050
}
51-
fn head_ty(&self) -> Option<Ty<'tcx>> {
51+
fn head_ty(&self, cx: MatchCtxt<'a, 'p, 'tcx>) -> Option<Ty<'tcx>> {
5252
if self.patterns.len() == 0 {
5353
return None;
5454
}
55-
// If the type is opaque and it is revealed anywhere in the column, we take the revealed
56-
// version. Otherwise we could encounter constructors for the revealed type and crash.
57-
let first_ty = self.patterns[0].ty();
58-
if RustcMatchCheckCtxt::is_opaque_ty(first_ty) {
59-
for pat in &self.patterns {
60-
let ty = pat.ty();
61-
if !RustcMatchCheckCtxt::is_opaque_ty(ty) {
62-
return Some(ty);
63-
}
64-
}
65-
}
66-
Some(first_ty)
55+
56+
let ty = self.patterns[0].ty();
57+
// FIXME(Nadrieril): `Cx` should only give us revealed types.
58+
Some(cx.tycx.reveal_opaque_ty(ty))
6759
}
6860

6961
/// Do constructor splitting on the constructors of the column.
@@ -125,7 +117,7 @@ fn collect_nonexhaustive_missing_variants<'a, 'p, 'tcx>(
125117
cx: MatchCtxt<'a, 'p, 'tcx>,
126118
column: &PatternColumn<'a, 'p, 'tcx>,
127119
) -> Vec<WitnessPat<'p, 'tcx>> {
128-
let Some(ty) = column.head_ty() else {
120+
let Some(ty) = column.head_ty(cx) else {
129121
return Vec::new();
130122
};
131123
let pcx = &PlaceCtxt::new_dummy(cx, ty);
@@ -226,7 +218,7 @@ pub(crate) fn lint_overlapping_range_endpoints<'a, 'p, 'tcx>(
226218
cx: MatchCtxt<'a, 'p, 'tcx>,
227219
column: &PatternColumn<'a, 'p, 'tcx>,
228220
) {
229-
let Some(ty) = column.head_ty() else {
221+
let Some(ty) = column.head_ty(cx) else {
230222
return;
231223
};
232224
let pcx = &PlaceCtxt::new_dummy(cx, ty);

‎compiler/rustc_pattern_analysis/src/rustc.rs

+19-2
Original file line numberDiff line numberDiff line change
@@ -44,6 +44,7 @@ pub type WitnessPat<'p, 'tcx> = crate::pat::WitnessPat<RustcMatchCheckCtxt<'p, '
4444
#[derive(Clone)]
4545
pub struct RustcMatchCheckCtxt<'p, 'tcx> {
4646
pub tcx: TyCtxt<'tcx>,
47+
pub typeck_results: &'tcx ty::TypeckResults<'tcx>,
4748
/// The module in which the match occurs. This is necessary for
4849
/// checking inhabited-ness of types because whether a type is (visibly)
4950
/// inhabited can depend on whether it was defined in the current module or
@@ -101,6 +102,21 @@ impl<'p, 'tcx> RustcMatchCheckCtxt<'p, 'tcx> {
101102
}
102103
}
103104

105+
/// Type inference occasionally gives us opaque types in places where corresponding patterns
106+
/// have more specific types. To avoid inconsistencies as well as detect opaque uninhabited
107+
/// types, we use the corresponding concrete type if possible.
108+
fn reveal_opaque_ty(&self, ty: Ty<'tcx>) -> Ty<'tcx> {
109+
if let ty::Alias(ty::Opaque, alias_ty) = ty.kind() {
110+
if let Some(local_def_id) = alias_ty.def_id.as_local() {
111+
let key = ty::OpaqueTypeKey { def_id: local_def_id, args: alias_ty.args };
112+
if let Some(real_ty) = self.typeck_results.concrete_opaque_types.get(&key) {
113+
return real_ty.ty;
114+
}
115+
}
116+
}
117+
ty
118+
}
119+
104120
// In the cases of either a `#[non_exhaustive]` field list or a non-public field, we hide
105121
// uninhabited fields in order not to reveal the uninhabitedness of the whole variant.
106122
// This lists the fields we keep along with their types.
@@ -873,8 +889,9 @@ impl<'p, 'tcx> TypeCx for RustcMatchCheckCtxt<'p, 'tcx> {
873889
fn is_exhaustive_patterns_feature_on(&self) -> bool {
874890
self.tcx.features().exhaustive_patterns
875891
}
876-
fn is_opaque_ty(ty: Self::Ty) -> bool {
877-
matches!(ty.kind(), ty::Alias(ty::Opaque, ..))
892+
893+
fn reveal_opaque_ty(&self, ty: Ty<'tcx>) -> Ty<'tcx> {
894+
self.reveal_opaque_ty(ty)
878895
}
879896

880897
fn ctor_arity(&self, ctor: &crate::constructor::Constructor<Self>, ty: Self::Ty) -> usize {

‎compiler/rustc_pattern_analysis/src/usefulness.rs

+5-15
Original file line numberDiff line numberDiff line change
@@ -865,24 +865,14 @@ impl<'a, 'p, Cx: TypeCx> Matrix<'a, 'p, Cx> {
865865
matrix
866866
}
867867

868-
fn head_ty(&self) -> Option<Cx::Ty> {
868+
fn head_ty(&self, mcx: MatchCtxt<'a, 'p, Cx>) -> Option<Cx::Ty> {
869869
if self.column_count() == 0 {
870870
return None;
871871
}
872872

873-
let mut ty = self.wildcard_row.head().ty();
874-
// If the type is opaque and it is revealed anywhere in the column, we take the revealed
875-
// version. Otherwise we could encounter constructors for the revealed type and crash.
876-
if Cx::is_opaque_ty(ty) {
877-
for pat in self.heads() {
878-
let pat_ty = pat.ty();
879-
if !Cx::is_opaque_ty(pat_ty) {
880-
ty = pat_ty;
881-
break;
882-
}
883-
}
884-
}
885-
Some(ty)
873+
let ty = self.wildcard_row.head().ty();
874+
// FIXME(Nadrieril): `Cx` should only give us revealed types.
875+
Some(mcx.tycx.reveal_opaque_ty(ty))
886876
}
887877
fn column_count(&self) -> usize {
888878
self.wildcard_row.len()
@@ -1181,7 +1171,7 @@ fn compute_exhaustiveness_and_usefulness<'a, 'p, Cx: TypeCx>(
11811171
) -> WitnessMatrix<Cx> {
11821172
debug_assert!(matrix.rows().all(|r| r.len() == matrix.column_count()));
11831173

1184-
let Some(ty) = matrix.head_ty() else {
1174+
let Some(ty) = matrix.head_ty(mcx) else {
11851175
// The base case: there are no columns in the matrix. We are morally pattern-matching on ().
11861176
// A row is useful iff it has no (unguarded) rows above it.
11871177
for row in matrix.rows_mut() {

‎tests/ui/pattern/usefulness/impl-trait.rs

+5-5
Original file line numberDiff line numberDiff line change
@@ -14,7 +14,7 @@ enum Void {}
1414
fn return_never_rpit(x: Void) -> impl Copy {
1515
if false {
1616
match return_never_rpit(x) {
17-
_ => {}
17+
_ => {} //~ ERROR unreachable
1818
}
1919
}
2020
x
@@ -28,7 +28,7 @@ type T = impl Copy;
2828
fn return_never_tait(x: Void) -> T {
2929
if false {
3030
match return_never_tait(x) {
31-
_ => {}
31+
_ => {} //~ ERROR unreachable
3232
}
3333
}
3434
x
@@ -42,7 +42,7 @@ fn option_never(x: Void) -> Option<impl Copy> {
4242
if false {
4343
match option_never(x) {
4444
None => {}
45-
Some(_) => {}
45+
Some(_) => {} //~ ERROR unreachable
4646
}
4747
match option_never(x) {
4848
None => {}
@@ -75,7 +75,7 @@ fn inner_never(x: Void) {
7575
type T = impl Copy;
7676
let y: T = x;
7777
match y {
78-
_ => {}
78+
_ => {} //~ ERROR unreachable
7979
}
8080
}
8181

@@ -93,7 +93,7 @@ type U = impl Copy;
9393
fn unify_never(x: Void, u: U) -> U {
9494
if false {
9595
match u {
96-
_ => {}
96+
_ => {} //~ ERROR unreachable
9797
}
9898
}
9999
x

‎tests/ui/pattern/usefulness/impl-trait.stderr

+34-4
Original file line numberDiff line numberDiff line change
@@ -1,21 +1,45 @@
11
error: unreachable pattern
2-
--> $DIR/impl-trait.rs:61:13
2+
--> $DIR/impl-trait.rs:17:13
33
|
4-
LL | Some(_) => {}
5-
| ^^^^^^^
4+
LL | _ => {}
5+
| ^
66
|
77
note: the lint level is defined here
88
--> $DIR/impl-trait.rs:5:9
99
|
1010
LL | #![deny(unreachable_patterns)]
1111
| ^^^^^^^^^^^^^^^^^^^^
1212

13+
error: unreachable pattern
14+
--> $DIR/impl-trait.rs:31:13
15+
|
16+
LL | _ => {}
17+
| ^
18+
19+
error: unreachable pattern
20+
--> $DIR/impl-trait.rs:45:13
21+
|
22+
LL | Some(_) => {}
23+
| ^^^^^^^
24+
25+
error: unreachable pattern
26+
--> $DIR/impl-trait.rs:61:13
27+
|
28+
LL | Some(_) => {}
29+
| ^^^^^^^
30+
1331
error: unreachable pattern
1432
--> $DIR/impl-trait.rs:65:13
1533
|
1634
LL | _ => {}
1735
| ^
1836

37+
error: unreachable pattern
38+
--> $DIR/impl-trait.rs:78:9
39+
|
40+
LL | _ => {}
41+
| ^
42+
1943
error: unreachable pattern
2044
--> $DIR/impl-trait.rs:88:9
2145
|
@@ -24,6 +48,12 @@ LL | _ => {}
2448
LL | Some((a, b)) => {}
2549
| ^^^^^^^^^^^^ unreachable pattern
2650

51+
error: unreachable pattern
52+
--> $DIR/impl-trait.rs:96:13
53+
|
54+
LL | _ => {}
55+
| ^
56+
2757
error: unreachable pattern
2858
--> $DIR/impl-trait.rs:107:9
2959
|
@@ -66,6 +96,6 @@ LL + _ => todo!(),
6696
LL + }
6797
|
6898

69-
error: aborting due to 7 previous errors
99+
error: aborting due to 12 previous errors
70100

71101
For more information about this error, try `rustc --explain E0004`.

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