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Auto merge of #125610 - oli-obk:define_opaque_types14, r=compiler-errors
Allow constraining opaque types during various unsizing casts allows unsizing of tuples, arrays and Adts to constraint opaque types in their generic parameters to concrete types on either side of the unsizing cast. Also allows constraining opaque types during trait object casts that only differ in auto traits or lifetimes. cc #116652
2 parents fc555cd + 45da035 commit 164e129

21 files changed

+330
-61
lines changed

‎compiler/rustc_trait_selection/src/traits/select/confirmation.rs

+4-4
Original file line numberDiff line numberDiff line change
@@ -1162,7 +1162,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
11621162
let InferOk { mut obligations, .. } = self
11631163
.infcx
11641164
.at(&obligation.cause, obligation.param_env)
1165-
.sup(DefineOpaqueTypes::No, target, source_trait)
1165+
.sup(DefineOpaqueTypes::Yes, target, source_trait)
11661166
.map_err(|_| Unimplemented)?;
11671167

11681168
// Register one obligation for 'a: 'b.
@@ -1229,7 +1229,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
12291229
let InferOk { obligations, .. } = self
12301230
.infcx
12311231
.at(&obligation.cause, obligation.param_env)
1232-
.eq(DefineOpaqueTypes::No, b, a)
1232+
.eq(DefineOpaqueTypes::Yes, b, a)
12331233
.map_err(|_| Unimplemented)?;
12341234

12351235
ImplSource::Builtin(BuiltinImplSource::Misc, obligations)
@@ -1277,7 +1277,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
12771277
let InferOk { obligations, .. } = self
12781278
.infcx
12791279
.at(&obligation.cause, obligation.param_env)
1280-
.eq(DefineOpaqueTypes::No, target, new_struct)
1280+
.eq(DefineOpaqueTypes::Yes, target, new_struct)
12811281
.map_err(|_| Unimplemented)?;
12821282
nested.extend(obligations);
12831283

@@ -1310,7 +1310,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
13101310
let InferOk { mut obligations, .. } = self
13111311
.infcx
13121312
.at(&obligation.cause, obligation.param_env)
1313-
.eq(DefineOpaqueTypes::No, target, new_tuple)
1313+
.eq(DefineOpaqueTypes::Yes, target, new_tuple)
13141314
.map_err(|_| Unimplemented)?;
13151315

13161316
// Add a nested `T: Unsize<U>` predicate.

‎tests/ui/impl-trait/trait_upcasting.rs

+26
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@@ -0,0 +1,26 @@
1+
//! Test that we allow unsizing `Trait<Concrete>` to `Trait<Opaque>` and vice versa
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3+
//@ check-pass
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5+
trait Trait<T> {}
6+
7+
impl<T, U> Trait<T> for U {}
8+
9+
fn hello() -> &'static (dyn Trait<impl Sized> + Send) {
10+
if false {
11+
let x = hello();
12+
let _: &'static dyn Trait<()> = x;
13+
}
14+
todo!()
15+
}
16+
17+
fn bye() -> &'static dyn Trait<impl Sized> {
18+
if false {
19+
let mut x = bye();
20+
let y: &'static (dyn Trait<()> + Send) = &();
21+
x = y;
22+
}
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todo!()
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}
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fn main() {}

‎tests/ui/impl-trait/trait_upcasting_reference_mismatch.rs

+18
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@@ -0,0 +1,18 @@
1+
//! Show an uninformative diagnostic that we could possibly improve in the future
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trait Trait<T> {}
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impl<T, U> Trait<T> for U {}
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fn hello() -> &'static (dyn Trait<impl Sized> + Send) {
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//~^ ERROR: type annotations needed
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if false {
10+
let x = hello();
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let _: &'static dyn Trait<()> = &x;
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//^ Note the extra `&`, paired with the blanket impl causing
13+
// `impl Sized` to never get a hidden type registered.
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}
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todo!()
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}
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fn main() {}

‎tests/ui/impl-trait/trait_upcasting_reference_mismatch.stderr

+9
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@@ -0,0 +1,9 @@
1+
error[E0282]: type annotations needed
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--> $DIR/trait_upcasting_reference_mismatch.rs:7:35
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|
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LL | fn hello() -> &'static (dyn Trait<impl Sized> + Send) {
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| ^^^^^^^^^^ cannot infer type
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error: aborting due to 1 previous error
8+
9+
For more information about this error, try `rustc --explain E0282`.

‎tests/ui/impl-trait/unsize_adt.rs

+3-2
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@@ -1,12 +1,13 @@
1-
//! Test that we do not allow unsizing `Foo<[Opaque; N]>` to `Foo<[Concrete]>`.
1+
//! Test that we allow unsizing `Foo<[Opaque; N]>` to `Foo<[Concrete]>`.
2+
3+
//@check-pass
24

35
struct Foo<T: ?Sized>(T);
46

57
fn hello() -> Foo<[impl Sized; 2]> {
68
if false {
79
let x = hello();
810
let _: &Foo<[i32]> = &x;
9-
//~^ ERROR: mismatched types
1011
}
1112
todo!()
1213
}

‎tests/ui/impl-trait/unsize_adt.stderr

-17
This file was deleted.

‎tests/ui/impl-trait/unsize_slice.rs

+3-2
Original file line numberDiff line numberDiff line change
@@ -1,10 +1,11 @@
1-
//! Test that we do not allow unsizing `[Opaque; N]` to `[Concrete]`.
1+
//! Test that we allow unsizing `[Opaque; N]` to `[Concrete]`.
2+
3+
//@check-pass
24

35
fn hello() -> [impl Sized; 2] {
46
if false {
57
let x = hello();
68
let _: &[i32] = &x;
7-
//~^ ERROR: mismatched types
89
}
910
todo!()
1011
}

‎tests/ui/impl-trait/unsize_slice.stderr

-17
This file was deleted.

‎tests/ui/impl-trait/unsize_tuple.rs

+3-2
Original file line numberDiff line numberDiff line change
@@ -1,12 +1,13 @@
1-
//! Test that we do not allow unsizing `([Opaque; N],)` to `([Concrete],)`.
1+
//! Test that we allow unsizing `([Opaque; N],)` to `([Concrete],)`.
2+
3+
//@check-pass
24

35
#![feature(unsized_tuple_coercion)]
46

57
fn hello() -> ([impl Sized; 2],) {
68
if false {
79
let x = hello();
810
let _: &([i32],) = &x;
9-
//~^ ERROR: mismatched types
1011
}
1112
todo!()
1213
}

‎tests/ui/impl-trait/unsize_tuple.stderr

-17
This file was deleted.

‎tests/ui/impl-trait/unsized_coercion.next.stderr

+26
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@@ -0,0 +1,26 @@
1+
error[E0271]: type mismatch resolving `impl Trait <: dyn Trait`
2+
--> $DIR/unsized_coercion.rs:14:17
3+
|
4+
LL | let x = hello();
5+
| ^^^^^^^ types differ
6+
7+
error[E0308]: mismatched types
8+
--> $DIR/unsized_coercion.rs:18:14
9+
|
10+
LL | fn hello() -> Box<impl Trait> {
11+
| ---------- the expected opaque type
12+
...
13+
LL | Box::new(1u32)
14+
| -------- ^^^^ types differ
15+
| |
16+
| arguments to this function are incorrect
17+
|
18+
= note: expected opaque type `impl Trait`
19+
found type `u32`
20+
note: associated function defined here
21+
--> $SRC_DIR/alloc/src/boxed.rs:LL:COL
22+
23+
error: aborting due to 2 previous errors
24+
25+
Some errors have detailed explanations: E0271, E0308.
26+
For more information about an error, try `rustc --explain E0271`.

‎tests/ui/impl-trait/unsized_coercion.rs

+21
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,21 @@
1+
//! This test checks that opaque types get unsized instead of
2+
//! constraining their hidden type to a trait object.
3+
4+
//@ revisions: next old
5+
//@[next] compile-flags: -Znext-solver
6+
//@[old] check-pass
7+
8+
trait Trait {}
9+
10+
impl Trait for u32 {}
11+
12+
fn hello() -> Box<impl Trait> {
13+
if true {
14+
let x = hello();
15+
//[next]~^ ERROR: type mismatch resolving `impl Trait <: dyn Trait`
16+
let y: Box<dyn Trait> = x;
17+
}
18+
Box::new(1u32) //[next]~ ERROR: mismatched types
19+
}
20+
21+
fn main() {}

‎tests/ui/impl-trait/unsized_coercion2.old.stderr

+12
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@@ -0,0 +1,12 @@
1+
error[E0277]: the size for values of type `impl Trait + ?Sized` cannot be known at compilation time
2+
--> $DIR/unsized_coercion2.rs:15:33
3+
|
4+
LL | let y: Box<dyn Trait> = x;
5+
| ^ doesn't have a size known at compile-time
6+
|
7+
= help: the trait `Sized` is not implemented for `impl Trait + ?Sized`
8+
= note: required for the cast from `Box<impl Trait + ?Sized>` to `Box<dyn Trait>`
9+
10+
error: aborting due to 1 previous error
11+
12+
For more information about this error, try `rustc --explain E0277`.

‎tests/ui/impl-trait/unsized_coercion2.rs

+21
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,21 @@
1+
//! This test checks that opaque types get unsized instead of
2+
//! constraining their hidden type to a trait object.
3+
4+
//@ revisions: next old
5+
//@[next] compile-flags: -Znext-solver
6+
//@[next] check-pass
7+
8+
trait Trait {}
9+
10+
impl Trait for u32 {}
11+
12+
fn hello() -> Box<impl Trait + ?Sized> {
13+
if true {
14+
let x = hello();
15+
let y: Box<dyn Trait> = x;
16+
//[old]~^ ERROR: the size for values of type `impl Trait + ?Sized` cannot be know
17+
}
18+
Box::new(1u32)
19+
}
20+
21+
fn main() {}

‎tests/ui/impl-trait/unsized_coercion3.next.stderr

+38
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,38 @@
1+
error[E0271]: type mismatch resolving `impl Trait + ?Sized <: dyn Send`
2+
--> $DIR/unsized_coercion3.rs:13:17
3+
|
4+
LL | let x = hello();
5+
| ^^^^^^^ types differ
6+
7+
error[E0308]: mismatched types
8+
--> $DIR/unsized_coercion3.rs:19:14
9+
|
10+
LL | fn hello() -> Box<impl Trait + ?Sized> {
11+
| ------------------- the expected opaque type
12+
...
13+
LL | Box::new(1u32)
14+
| -------- ^^^^ types differ
15+
| |
16+
| arguments to this function are incorrect
17+
|
18+
= note: expected opaque type `impl Trait + ?Sized`
19+
found type `u32`
20+
note: associated function defined here
21+
--> $SRC_DIR/alloc/src/boxed.rs:LL:COL
22+
23+
error[E0277]: the size for values of type `impl Trait + ?Sized` cannot be known at compilation time
24+
--> $DIR/unsized_coercion3.rs:19:14
25+
|
26+
LL | Box::new(1u32)
27+
| -------- ^^^^ doesn't have a size known at compile-time
28+
| |
29+
| required by a bound introduced by this call
30+
|
31+
= help: the trait `Sized` is not implemented for `impl Trait + ?Sized`
32+
note: required by a bound in `Box::<T>::new`
33+
--> $SRC_DIR/alloc/src/boxed.rs:LL:COL
34+
35+
error: aborting due to 3 previous errors
36+
37+
Some errors have detailed explanations: E0271, E0277, E0308.
38+
For more information about an error, try `rustc --explain E0271`.

‎tests/ui/impl-trait/unsized_coercion3.old.stderr

+26
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,26 @@
1+
error: cannot check whether the hidden type of opaque type satisfies auto traits
2+
--> $DIR/unsized_coercion3.rs:15:32
3+
|
4+
LL | let y: Box<dyn Send> = x;
5+
| ^
6+
|
7+
= note: fetching the hidden types of an opaque inside of the defining scope is not supported. You can try moving the opaque type and the item that actually registers a hidden type into a new submodule
8+
note: opaque type is declared here
9+
--> $DIR/unsized_coercion3.rs:11:19
10+
|
11+
LL | fn hello() -> Box<impl Trait + ?Sized> {
12+
| ^^^^^^^^^^^^^^^^^^^
13+
= note: required for the cast from `Box<impl Trait + ?Sized>` to `Box<dyn Send>`
14+
15+
error[E0277]: the size for values of type `impl Trait + ?Sized` cannot be known at compilation time
16+
--> $DIR/unsized_coercion3.rs:15:32
17+
|
18+
LL | let y: Box<dyn Send> = x;
19+
| ^ doesn't have a size known at compile-time
20+
|
21+
= help: the trait `Sized` is not implemented for `impl Trait + ?Sized`
22+
= note: required for the cast from `Box<impl Trait + ?Sized>` to `Box<dyn Send>`
23+
24+
error: aborting due to 2 previous errors
25+
26+
For more information about this error, try `rustc --explain E0277`.

‎tests/ui/impl-trait/unsized_coercion3.rs

+24
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,24 @@
1+
//! This test checks that opaque types get unsized instead of
2+
//! constraining their hidden type to a trait object.
3+
4+
//@ revisions: next old
5+
//@[next] compile-flags: -Znext-solver
6+
7+
trait Trait {}
8+
9+
impl Trait for u32 {}
10+
11+
fn hello() -> Box<impl Trait + ?Sized> {
12+
if true {
13+
let x = hello();
14+
//[next]~^ ERROR: type mismatch resolving `impl Trait + ?Sized <: dyn Send`
15+
let y: Box<dyn Send> = x;
16+
//[old]~^ ERROR: the size for values of type `impl Trait + ?Sized` cannot be know
17+
//[old]~| ERROR: cannot check whether the hidden type of opaque type satisfies auto traits
18+
}
19+
Box::new(1u32)
20+
//[next]~^ ERROR: mismatched types
21+
//[next]~| ERROR: the size for values of type `impl Trait + ?Sized` cannot be know
22+
}
23+
24+
fn main() {}

‎tests/ui/impl-trait/unsized_coercion4.rs

+20
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,20 @@
1+
//! This test checks that opaque types get unsized instead of
2+
//! constraining their hidden type to a trait object.
3+
4+
//@ revisions: next old
5+
//@[next] compile-flags: -Znext-solver
6+
//@check-pass
7+
8+
trait Trait {}
9+
10+
impl Trait for u32 {}
11+
12+
fn hello() -> Box<impl Trait + ?Sized> {
13+
if true {
14+
let x = hello() as Box<u32>;
15+
let y: Box<dyn Send> = x;
16+
}
17+
Box::new(1u32)
18+
}
19+
20+
fn main() {}

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