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https://github.com/rust-lang/rust
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coherence: don't add hidden types for opaques
we can otherwise assign a hidden type to the opaque which causes ICE if we don't use `take_opaque_types` during coherence. This is annoying so I didn't bother. Added a test showing the behavior this prevents.
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@ -533,17 +533,29 @@ fn register_hidden_type(
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// these are the same span, but not in cases like `-> (impl
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// Foo, impl Bar)`.
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let span = cause.span;
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let prev = self.inner.borrow_mut().opaque_types().register(
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opaque_type_key,
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OpaqueHiddenType { ty: hidden_ty, span },
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origin,
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);
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let mut obligations = if let Some(prev) = prev {
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self.at(&cause, param_env)
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.eq_exp(DefineOpaqueTypes::Yes, a_is_expected, prev, hidden_ty)?
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.obligations
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let mut obligations = if self.intercrate {
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// During intercrate we do not define opaque types but instead always
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// force ambiguity unless the hidden type is known to not implement
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// our trait.
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vec![traits::Obligation::new(
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self.tcx,
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cause.clone(),
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param_env,
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ty::PredicateKind::Ambiguous,
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)]
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} else {
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Vec::new()
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let prev = self.inner.borrow_mut().opaque_types().register(
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opaque_type_key,
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OpaqueHiddenType { ty: hidden_ty, span },
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origin,
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);
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if let Some(prev) = prev {
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self.at(&cause, param_env)
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.eq_exp(DefineOpaqueTypes::Yes, a_is_expected, prev, hidden_ty)?
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.obligations
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} else {
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Vec::new()
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}
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};
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self.add_item_bounds_for_hidden_type(
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@ -0,0 +1,25 @@
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// When checking whether these two impls overlap, we could detect that we
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// would require the hidden type of `TAIT` to be equal to both `u32` and `i32`
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// and therefore accept them as disjoint. That is annoying to implement with
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// the current system because we would have to add the following to each
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// returning branch in coherence.
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//
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// let _ = infcx.take_opaque_types();
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//
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// @lcnr: Because of this I decided to not bother and cause this to fail instead.
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// In the future we can definitely modify the compiler to accept this
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// again.
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#![feature(type_alias_impl_trait)]
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trait Trait {}
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type TAIT = impl Sized;
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impl Trait for (TAIT, TAIT) {}
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impl Trait for (u32, i32) {}
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//~^ ERROR conflicting implementations of trait `Trait` for type `(TAIT, TAIT)`
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fn define() -> TAIT {}
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fn main() {}
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@ -0,0 +1,12 @@
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error[E0119]: conflicting implementations of trait `Trait` for type `(TAIT, TAIT)`
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--> $DIR/coherence_different_hidden_ty.rs:20:1
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LL | impl Trait for (TAIT, TAIT) {}
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| --------------------------- first implementation here
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LL |
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LL | impl Trait for (u32, i32) {}
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| ^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `(TAIT, TAIT)`
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error: aborting due to previous error
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For more information about this error, try `rustc --explain E0119`.
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