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Auto merge of #71896 - spastorino:existential-assoc-types-variance, r=nikomatsakis
Relate existential associated types with variance Invariant Fixes #71550 #72315 r? @nikomatsakis The test case reported in that issue now errors with the following message ... ``` error[E0495]: cannot infer an appropriate lifetime for lifetime parameter 'a in function call due to conflicting requirements --> /tmp/test.rs:25:5 | 25 | bad(&Bar(PhantomData), x) | ^^^^^^^^^^^^^^^^^^^^^^^^^ | note: first, the lifetime cannot outlive the lifetime `'a` as defined on the function body at 24:11... --> /tmp/test.rs:24:11 | 24 | fn extend<'a, T>(x: &'a T) -> &'static T { | ^^ note: ...so that reference does not outlive borrowed content --> /tmp/test.rs:25:28 | 25 | bad(&Bar(PhantomData), x) | ^ = note: but, the lifetime must be valid for the static lifetime... note: ...so that the types are compatible --> /tmp/test.rs:25:9 | 25 | bad(&Bar(PhantomData), x) | ^^^^^^^^^^^^^^^^^ = note: expected `&'static T` found `&T` error: aborting due to previous error For more information about this error, try `rustc --explain E0495`. ``` I could also add that test case if we want to have a weaponized one too.
2 parents e93cb96 + c99164e commit 3ddf480

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-5
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‎src/librustc_middle/ty/relate.rs

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@@ -250,8 +250,8 @@ impl<'tcx> Relate<'tcx> for ty::ExistentialProjection<'tcx> {
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&b.item_def_id,
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)))
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} else {
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let ty = relation.relate(&a.ty, &b.ty)?;
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let substs = relation.relate(&a.substs, &b.substs)?;
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let ty = relation.relate_with_variance(ty::Invariant, &a.ty, &b.ty)?;
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let substs = relation.relate_with_variance(ty::Invariant, &a.substs, &b.substs)?;
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Ok(ty::ExistentialProjection { item_def_id: a.item_def_id, substs, ty })
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}
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}

‎src/test/ui/coercion/coerce-expect-unsized-ascribed.stderr

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@@ -121,7 +121,7 @@ error[E0308]: mismatched types
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LL | let _ = Box::new(|x| (x as u8)): Box<dyn Fn(i32) -> _>;
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| ^^^^^^^^^^^^^^^^^^^^^^^ expected trait object `dyn std::ops::Fn`, found closure
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|
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= note: expected struct `std::boxed::Box<dyn std::ops::Fn(i32) -> _>`
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= note: expected struct `std::boxed::Box<dyn std::ops::Fn(i32) -> u8>`
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found struct `std::boxed::Box<[closure@$DIR/coerce-expect-unsized-ascribed.rs:26:22: 26:35]>`
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error: aborting due to 14 previous errors

‎src/test/ui/issues/issue-20605.stderr

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@@ -1,10 +1,10 @@
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error[E0277]: the size for values of type `dyn std::iter::Iterator<Item = &mut u8>` cannot be known at compilation time
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error[E0277]: the size for values of type `dyn std::iter::Iterator<Item = &'a mut u8>` cannot be known at compilation time
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--> $DIR/issue-20605.rs:2:17
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|
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LL | for item in *things { *item = 0 }
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| ^^^^^^^ doesn't have a size known at compile-time
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|
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= help: the trait `std::marker::Sized` is not implemented for `dyn std::iter::Iterator<Item = &mut u8>`
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= help: the trait `std::marker::Sized` is not implemented for `dyn std::iter::Iterator<Item = &'a mut u8>`
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= note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>
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= note: required by `std::iter::IntoIterator::into_iter`
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‎src/test/ui/variance/variance-associated-types2.nll.stderr

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@@ -0,0 +1,12 @@
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error: lifetime may not live long enough
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--> $DIR/variance-associated-types2.rs:13:12
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|
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LL | fn take<'a>(_: &'a u32) {
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| -- lifetime `'a` defined here
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LL | let _: Box<dyn Foo<Bar = &'a u32>> = make();
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^ type annotation requires that `'a` must outlive `'static`
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|
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= help: consider replacing `'a` with `'static`
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error: aborting due to previous error
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‎src/test/ui/variance/variance-associated-types2.rs

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// Test that dyn Foo<Bar = T> is invariant with respect to T.
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// Failure to enforce invariance here can be weaponized, see #71550 for details.
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trait Foo {
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type Bar;
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}
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fn make() -> Box<dyn Foo<Bar = &'static u32>> {
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panic!()
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}
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fn take<'a>(_: &'a u32) {
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let _: Box<dyn Foo<Bar = &'a u32>> = make();
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//~^ ERROR mismatched types [E0308]
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}
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fn main() {}

‎src/test/ui/variance/variance-associated-types2.stderr

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error[E0308]: mismatched types
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--> $DIR/variance-associated-types2.rs:13:42
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|
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LL | let _: Box<dyn Foo<Bar = &'a u32>> = make();
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| ^^^^^^ lifetime mismatch
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|
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= note: expected trait object `dyn Foo<Bar = &'a u32>`
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found trait object `dyn Foo<Bar = &'static u32>`
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note: the lifetime `'a` as defined on the function body at 12:9...
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--> $DIR/variance-associated-types2.rs:12:9
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|
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LL | fn take<'a>(_: &'a u32) {
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| ^^
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= note: ...does not necessarily outlive the static lifetime
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error: aborting due to previous error
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For more information about this error, try `rustc --explain E0308`.

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