stabilize -Znext-solver=coherence

rust-lang · Mar 1, 2024 · 8f16e02 · 8f16e02
1 parent 6cbf092
commit 8f16e02
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diff --git a/compiler/rustc_session/src/config.rs b/compiler/rustc_session/src/config.rs
@@ -736,6 +736,16 @@ pub struct NextSolverConfig {
     pub dump_tree: DumpSolverProofTree,
 }
 
+impl Default for NextSolverConfig {
+    fn default() -> Self {
+        NextSolverConfig {
+            coherence: true,
+            globally: false,
+            dump_tree: DumpSolverProofTree::default(),
+        }
+    }
+}
+
 #[derive(Default, Debug, Copy, Clone, Hash, PartialEq, Eq)]
 pub enum DumpSolverProofTree {
     Always,

diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
@@ -1023,6 +1023,10 @@ mod parse {
             let mut dump_tree = None;
             for c in config.split(',') {
                 match c {
+                    "no" => {
+                        *slot = None;
+                        return true;
+                    }
                     "globally" => globally = true,
                     "coherence" => {
                         globally = false;
@@ -1736,7 +1740,7 @@ options! {
         "the size at which the `large_assignments` lint starts to be emitted"),
     mutable_noalias: bool = (true, parse_bool, [TRACKED],
         "emit noalias metadata for mutable references (default: yes)"),
-    next_solver: Option<NextSolverConfig> = (None, parse_next_solver_config, [TRACKED],
+    next_solver: Option<NextSolverConfig> = (Some(NextSolverConfig::default()), parse_next_solver_config, [TRACKED],
         "enable and configure the next generation trait solver used by rustc"),
     nll_facts: bool = (false, parse_bool, [UNTRACKED],
         "dump facts from NLL analysis into side files (default: no)"),

diff --git a/tests/ui/associated-types/associated-types-coherence-failure.stderr b/tests/ui/associated-types/associated-types-coherence-failure.stderr
@@ -1,20 +1,20 @@
-error[E0119]: conflicting implementations of trait `IntoCow<'_, _>` for type `Cow<'_, _>`
+error[E0119]: conflicting implementations of trait `IntoCow<'_, _>` for type `<_ as ToOwned>::Owned`
   --> $DIR/associated-types-coherence-failure.rs:21:1
    |
 LL | impl<'a, B: ?Sized> IntoCow<'a, B> for <B as ToOwned>::Owned where B: ToOwned {
    | ----------------------------------------------------------------------------- first implementation here
 ...
 LL | impl<'a, B: ?Sized> IntoCow<'a, B> for Cow<'a, B> where B: ToOwned {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `Cow<'_, _>`
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `<_ as ToOwned>::Owned`
 
-error[E0119]: conflicting implementations of trait `IntoCow<'_, _>` for type `&_`
+error[E0119]: conflicting implementations of trait `IntoCow<'_, _>` for type `<_ as ToOwned>::Owned`
   --> $DIR/associated-types-coherence-failure.rs:28:1
    |
 LL | impl<'a, B: ?Sized> IntoCow<'a, B> for <B as ToOwned>::Owned where B: ToOwned {
    | ----------------------------------------------------------------------------- first implementation here
 ...
 LL | impl<'a, B: ?Sized> IntoCow<'a, B> for &'a B where B: ToOwned {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `&_`
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `<_ as ToOwned>::Owned`
 
 error: aborting due to 2 previous errors
 

diff --git a/tests/ui/coherence/coherence-negative-outlives-lifetimes.stock.stderr b/tests/ui/coherence/coherence-negative-outlives-lifetimes.stock.stderr
@@ -5,6 +5,8 @@ LL | impl<'a, T: MyPredicate<'a>> MyTrait<'a> for T {}
    | ---------------------------------------------- first implementation here
 LL | impl<'a, T> MyTrait<'a> for &'a T {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `&_`
+   |
+   = note: downstream crates may implement trait `MyPredicate<'_>` for type `&_`
 
 error: aborting due to 1 previous error
 

diff --git a/tests/ui/coherence/coherence-negative-outlives-lifetimes.with_negative_coherence.stderr b/tests/ui/coherence/coherence-negative-outlives-lifetimes.with_negative_coherence.stderr
@@ -5,6 +5,8 @@ LL | impl<'a, T: MyPredicate<'a>> MyTrait<'a> for T {}
    | ---------------------------------------------- first implementation here
 LL | impl<'a, T> MyTrait<'a> for &'a T {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `&_`
+   |
+   = note: downstream crates may implement trait `MyPredicate<'_>` for type `&_`
 
 error: aborting due to 1 previous error
 

diff --git a/tests/ui/coherence/coherence-overlap-negate-not-use-feature-gate.stderr b/tests/ui/coherence/coherence-overlap-negate-not-use-feature-gate.stderr
@@ -5,6 +5,8 @@ LL | impl<T: DerefMut> Foo for T {}
    | --------------------------- first implementation here
 LL | impl<U> Foo for &U {}
    | ^^^^^^^^^^^^^^^^^^ conflicting implementation for `&_`
+   |
+   = note: downstream crates may implement trait `std::ops::DerefMut` for type `&_`
 
 error: aborting due to 1 previous error
 

diff --git a/tests/ui/coherence/negative-coherence-check-placeholder-outlives.stderr b/tests/ui/coherence/negative-coherence-check-placeholder-outlives.stderr
@@ -5,6 +5,8 @@ LL | impl<T> Bar for T where T: Foo {}
    | ------------------------------ first implementation here
 LL | impl<T> Bar for Box<T> {}
    | ^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `Box<_>`
+   |
+   = note: downstream crates may implement trait `Foo` for type `std::boxed::Box<_>`
 
 error: aborting due to 1 previous error
 

diff --git a/tests/ui/coherence/negative-coherence-considering-regions.any_lt.stderr b/tests/ui/coherence/negative-coherence-considering-regions.any_lt.stderr
@@ -6,6 +6,8 @@ LL | impl<T> Bar for T where T: Foo {}
 ...
 LL | impl<T> Bar for &T {}
    | ^^^^^^^^^^^^^^^^^^ conflicting implementation for `&_`
+   |
+   = note: downstream crates may implement trait `Foo` for type `&_`
 
 error: aborting due to 1 previous error
 

diff --git a/...oherence/negative-coherence-placeholder-region-constraints-on-unification.explicit.stderr b/...oherence/negative-coherence-placeholder-region-constraints-on-unification.explicit.stderr
@@ -8,6 +8,7 @@ LL | impl<T: ?Sized> FnMarker for fn(&T) {}
    |
    = warning: the behavior may change in a future release
    = note: for more information, see issue #56105 <https://github.com/rust-lang/rust/issues/56105>
+   = note: downstream crates may implement trait `Marker` for type `&_`
    = note: this behavior recently changed as a result of a bug fix; see rust-lang/rust#56105 for details
 note: the lint level is defined here
   --> $DIR/negative-coherence-placeholder-region-constraints-on-unification.rs:4:11

diff --git a/tests/ui/coherence/normalize-for-errors.current.stderr b/tests/ui/coherence/normalize-for-errors.current.stderr
@@ -1,11 +1,11 @@
-error[E0119]: conflicting implementations of trait `MyTrait<_>` for type `(Box<(MyType,)>, _)`
+error[E0119]: conflicting implementations of trait `MyTrait<_>` for type `(Box<(MyType,)>, <_ as Iterator>::Item)`
   --> $DIR/normalize-for-errors.rs:16:1
    |
 LL | impl<T: Copy, S: Iterator> MyTrait<S> for (T, S::Item) {}
    | ------------------------------------------------------ first implementation here
 LL |
 LL | impl<S: Iterator> MyTrait<S> for (Box<<(MyType,) as Mirror>::Assoc>, S::Item) {}
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `(Box<(MyType,)>, _)`
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `(Box<(MyType,)>, <_ as Iterator>::Item)`
    |
    = note: upstream crates may add a new impl of trait `std::marker::Copy` for type `std::boxed::Box<(MyType,)>` in future versions
 

diff --git a/tests/ui/coherence/occurs-check/associated-type.old.stderr b/tests/ui/coherence/occurs-check/associated-type.old.stderr
@@ -1,12 +1,8 @@
 WARN rustc_infer::infer::relate::generalize may incompletely handle alias type: AliasTy { args: [*const ?1t, ReBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed(DefId(0:27 ~ associated_type[f554]::{impl#3}::'a#1), 'a) })], def_id: DefId(0:5 ~ associated_type[f554]::ToUnit::Unit) }
-WARN rustc_infer::infer::relate::generalize may incompletely handle alias type: AliasTy { args: [*const ?1t, RePlaceholder(!2_BoundRegion { var: 0, kind: BrNamed(DefId(0:27 ~ associated_type[f554]::{impl#3}::'a#1), 'a) })], def_id: DefId(0:5 ~ associated_type[f554]::ToUnit::Unit) }
 WARN rustc_infer::infer::relate::generalize may incompletely handle alias type: AliasTy { args: [*const ?1t, ReBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed(DefId(0:27 ~ associated_type[f554]::{impl#3}::'a#1), 'a) })], def_id: DefId(0:5 ~ associated_type[f554]::ToUnit::Unit) }
-WARN rustc_infer::infer::relate::generalize may incompletely handle alias type: AliasTy { args: [*const ?1t, RePlaceholder(!2_BoundRegion { var: 0, kind: BrNamed(DefId(0:27 ~ associated_type[f554]::{impl#3}::'a#1), 'a) })], def_id: DefId(0:5 ~ associated_type[f554]::ToUnit::Unit) }
 WARN rustc_infer::infer::relate::generalize may incompletely handle alias type: AliasTy { args: [*const ?1t, ReBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed(DefId(0:27 ~ associated_type[f554]::{impl#3}::'a#1), 'a) })], def_id: DefId(0:5 ~ associated_type[f554]::ToUnit::Unit) }
-WARN rustc_infer::infer::relate::generalize may incompletely handle alias type: AliasTy { args: [*const ?1t, RePlaceholder(!2_BoundRegion { var: 0, kind: BrNamed(DefId(0:27 ~ associated_type[f554]::{impl#3}::'a#1), 'a) })], def_id: DefId(0:5 ~ associated_type[f554]::ToUnit::Unit) }
 WARN rustc_infer::infer::relate::generalize may incompletely handle alias type: AliasTy { args: [*const ?1t, ReBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed(DefId(0:27 ~ associated_type[f554]::{impl#3}::'a#1), 'a) })], def_id: DefId(0:5 ~ associated_type[f554]::ToUnit::Unit) }
-WARN rustc_infer::infer::relate::generalize may incompletely handle alias type: AliasTy { args: [*const ?1t, RePlaceholder(!2_BoundRegion { var: 0, kind: BrNamed(DefId(0:27 ~ associated_type[f554]::{impl#3}::'a#1), 'a) })], def_id: DefId(0:5 ~ associated_type[f554]::ToUnit::Unit) }
-error[E0119]: conflicting implementations of trait `Overlap<for<'a> fn(&'a (), _)>` for type `for<'a> fn(&'a (), _)`
+error[E0119]: conflicting implementations of trait `Overlap<for<'a> fn(&'a (), ())>` for type `for<'a> fn(&'a (), ())`
   --> $DIR/associated-type.rs:31:1
    |
 LL |   impl<T> Overlap<T> for T {
@@ -16,7 +12,7 @@ LL | / impl<T> Overlap<for<'a> fn(&'a (), Assoc<'a, T>)> for T
 LL | |
 LL | | where
 LL | |     for<'a> *const T: ToUnit<'a>,
-   | |_________________________________^ conflicting implementation for `for<'a> fn(&'a (), _)`
+   | |_________________________________^ conflicting implementation for `for<'a> fn(&'a (), ())`
    |
    = note: this behavior recently changed as a result of a bug fix; see rust-lang/rust#56105 for details
 

diff --git a/tests/ui/coherence/occurs-check/opaques.current.stderr b/tests/ui/coherence/occurs-check/opaques.current.stderr
@@ -0,0 +1,12 @@
+error[E0119]: conflicting implementations of trait `Trait<_>`
+  --> $DIR/opaques.rs:27:1
+   |
+LL | impl<T> Trait<T> for T {
+   | ---------------------- first implementation here
+...
+LL | impl<T> Trait<T> for defining_scope::Alias<T> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0119`.
diff --git a/tests/ui/coherence/occurs-check/opaques.next.stderr b/tests/ui/coherence/occurs-check/opaques.next.stderr
@@ -1,5 +1,5 @@
 error[E0119]: conflicting implementations of trait `Trait<_>`
-  --> $DIR/opaques.rs:30:1
+  --> $DIR/opaques.rs:27:1
    |
 LL | impl<T> Trait<T> for T {
    | ---------------------- first implementation here
@@ -8,7 +8,7 @@ LL | impl<T> Trait<T> for defining_scope::Alias<T> {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation
 
 error[E0282]: type annotations needed
-  --> $DIR/opaques.rs:13:20
+  --> $DIR/opaques.rs:10:20
    |
 LL |     pub fn cast<T>(x: Container<Alias<T>, T>) -> Container<T, T> {
    |                    ^ cannot infer type for struct `Container<T, T>`

diff --git a/tests/ui/coherence/occurs-check/opaques.rs b/tests/ui/coherence/occurs-check/opaques.rs
@@ -1,10 +1,7 @@
-//@revisions: old next
+//@revisions: current next
 //@[next] compile-flags: -Znext-solver
 
 // A regression test for #105787
-
-//@[old] known-bug: #105787
-//@[old] check-pass
 #![feature(type_alias_impl_trait)]
 mod defining_scope {
     use super::*;
@@ -28,7 +25,7 @@ impl<T> Trait<T> for T {
     type Assoc = Box<u32>;
 }
 impl<T> Trait<T> for defining_scope::Alias<T> {
-    //[next]~^ ERROR conflicting implementations of trait
+    //~^ ERROR conflicting implementations of trait
     type Assoc = usize;
 }
 

diff --git a/tests/ui/dyn-star/param-env-region-infer.rs b/tests/ui/dyn-star/param-env-region-infer.rs
@@ -1,7 +1,7 @@
 //@ revisions: current
 //@ incremental
 
-// FIXME(-Znext-solver): THis currently results in unstable query results:
+// FIXME(-Znext-solver): This currently results in unstable query results:
 // `normalizes-to(opaque, opaque)` changes from `Maybe(Ambiguous)` to `Maybe(Overflow)`
 // once the hidden type of the opaque is already defined to be itself.
 

diff --git a/tests/ui/error-codes/e0119/issue-23563.stderr b/tests/ui/error-codes/e0119/issue-23563.stderr
@@ -1,4 +1,4 @@
-error[E0119]: conflicting implementations of trait `LolFrom<&[_]>` for type `LocalType<_>`
+error[E0119]: conflicting implementations of trait `LolFrom<&[u8]>` for type `LocalType<u8>`
   --> $DIR/issue-23563.rs:13:1
    |
 LL | impl<'a, T> LolFrom<&'a [T]> for LocalType<T> {

diff --git a/tests/ui/feature-gates/feature-gate-with_negative_coherence.stderr b/tests/ui/feature-gates/feature-gate-with_negative_coherence.stderr
@@ -6,6 +6,8 @@ LL | impl<T: std::ops::DerefMut> Foo for T { }
 LL |
 LL | impl<T> Foo for &T { }
    | ^^^^^^^^^^^^^^^^^^ conflicting implementation for `&_`
+   |
+   = note: downstream crates may implement trait `std::ops::DerefMut` for type `&_`
 
 error: aborting due to 1 previous error
 

diff --git a/tests/ui/impl-trait/auto-trait-coherence.old.stderr b/tests/ui/impl-trait/auto-trait-coherence.old.stderr
@@ -1,11 +1,11 @@
-error[E0119]: conflicting implementations of trait `AnotherTrait` for type `D<OpaqueType>`
+error[E0119]: conflicting implementations of trait `AnotherTrait` for type `D<_>`
   --> $DIR/auto-trait-coherence.rs:24:1
    |
 LL | impl<T: Send> AnotherTrait for T {}
    | -------------------------------- first implementation here
 ...
 LL | impl AnotherTrait for D<OpaqueType> {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `D<OpaqueType>`
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `D<_>`
 
 error: aborting due to 1 previous error
 

diff --git a/tests/ui/impl-trait/auto-trait-coherence.rs b/tests/ui/impl-trait/auto-trait-coherence.rs
@@ -1,6 +1,3 @@
-//@ revisions: old next
-//@[next] compile-flags: -Znext-solver
-
 // Tests that type alias impls traits do not leak auto-traits for
 // the purposes of coherence checking
 #![feature(type_alias_impl_trait)]
@@ -22,8 +19,7 @@ impl<T: Send> AnotherTrait for T {}
 // (We treat opaque types as "foreign types" that could grow more impls
 // in the future.)
 impl AnotherTrait for D<OpaqueType> {
-    //[old]~^ ERROR conflicting implementations of trait `AnotherTrait` for type `D<OpaqueType>`
-    //[next]~^^ ERROR conflicting implementations of trait `AnotherTrait` for type `D<_>`
+    //~^ ERROR conflicting implementations of trait `AnotherTrait` for type `D<_>`
 }
 
 fn main() {}
diff --git a/tests/ui/impl-trait/auto-trait-coherence.stderr b/tests/ui/impl-trait/auto-trait-coherence.stderr
@@ -0,0 +1,12 @@
+error[E0119]: conflicting implementations of trait `AnotherTrait` for type `D<_>`
+  --> $DIR/auto-trait-coherence.rs:21:1
+   |
+LL | impl<T: Send> AnotherTrait for T {}
+   | -------------------------------- first implementation here
+...
+LL | impl AnotherTrait for D<OpaqueType> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `D<_>`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0119`.
diff --git a/tests/ui/impl-trait/coherence-treats-tait-ambig.rs b/tests/ui/impl-trait/coherence-treats-tait-ambig.rs
@@ -5,7 +5,7 @@ type T = impl Sized;
 struct Foo;
 
 impl Into<T> for Foo {
-//~^ ERROR conflicting implementations of trait `Into<T>` for type `Foo`
+//~^ ERROR conflicting implementations of trait `Into<_>` for type `Foo`
     fn into(self) -> T {
         Foo
     }

diff --git a/tests/ui/impl-trait/coherence-treats-tait-ambig.stderr b/tests/ui/impl-trait/coherence-treats-tait-ambig.stderr
@@ -1,4 +1,4 @@
-error[E0119]: conflicting implementations of trait `Into<T>` for type `Foo`
+error[E0119]: conflicting implementations of trait `Into<_>` for type `Foo`
   --> $DIR/coherence-treats-tait-ambig.rs:7:1
    |
 LL | impl Into<T> for Foo {

diff --git a/tests/ui/impl-trait/negative-reasoning.rs b/tests/ui/impl-trait/negative-reasoning.rs
@@ -17,7 +17,7 @@ impl<T: std::fmt::Debug> AnotherTrait for T {}
 
 // This is in error, because we cannot assume that `OpaqueType: !Debug`
 impl AnotherTrait for D<OpaqueType> {
-    //~^ ERROR conflicting implementations of trait `AnotherTrait` for type `D<OpaqueType>`
+    //~^ ERROR conflicting implementations of trait `AnotherTrait` for type `D<_>`
 }
 
 fn main() {}
diff --git a/tests/ui/impl-trait/negative-reasoning.stderr b/tests/ui/impl-trait/negative-reasoning.stderr
@@ -1,13 +1,11 @@
-error[E0119]: conflicting implementations of trait `AnotherTrait` for type `D<OpaqueType>`
+error[E0119]: conflicting implementations of trait `AnotherTrait` for type `D<_>`
   --> $DIR/negative-reasoning.rs:19:1
    |
 LL | impl<T: std::fmt::Debug> AnotherTrait for T {}
    | ------------------------------------------- first implementation here
 ...
 LL | impl AnotherTrait for D<OpaqueType> {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `D<OpaqueType>`
-   |
-   = note: upstream crates may add a new impl of trait `std::marker::FnPtr` for type `OpaqueType` in future versions
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `D<_>`
 
 error: aborting due to 1 previous error
 

diff --git a/tests/ui/impl-unused-tps.rs b/tests/ui/impl-unused-tps.rs
@@ -1,63 +1,69 @@
-//~ ERROR overflow evaluating the requirement `([isize; 0], _): Sized
-
 trait Foo<A> {
-    fn get(&self, A: &A) { }
+    fn get(&self, A: &A) {}
 }
 
 trait Bar {
     type Out;
 }
 
-impl<T> Foo<T> for [isize;0] {
+impl<T> Foo<T> for [isize; 0] {
     // OK, T is used in `Foo<T>`.
 }
 
-impl<T,U> Foo<T> for [isize;1] {
+impl<T, U> Foo<T> for [isize; 1] {
     //~^ ERROR the type parameter `U` is not constrained
 }
 
-impl<T,U> Foo<T> for [isize;2] where T : Bar<Out=U> {
+impl<T, U> Foo<T> for [isize; 2]
+where
+    T: Bar<Out = U>,
+{
     // OK, `U` is now constrained by the output type parameter.
 }
 
-impl<T:Bar<Out=U>,U> Foo<T> for [isize;3] {
+impl<T: Bar<Out = U>, U> Foo<T> for [isize; 3] {
     // OK, same as above but written differently.
 }
 
-impl<T,U> Foo<T> for U {
+impl<T, U> Foo<T> for U {
     //~^ ERROR conflicting implementations of trait `Foo<_>` for type `[isize; 0]`
 }
 
-impl<T,U> Bar for T {
+impl<T, U> Bar for T {
     //~^ ERROR the type parameter `U` is not constrained
 
     type Out = U;
 
     // Using `U` in an associated type within the impl is not good enough!
 }
 
-impl<T,U> Bar for T
-    where T : Bar<Out=U>
+impl<T, U> Bar for T
+where
+    T: Bar<Out = U>,
 {
-    //~^^^ ERROR the type parameter `U` is not constrained
-
+    //~^^^^ ERROR the type parameter `U` is not constrained by the impl trait, self type, or predicates
+    //~| ERROR conflicting implementations of trait `Bar`
     // This crafty self-referential attempt is still no good.
 }
 
-impl<T,U,V> Foo<T> for T
-    where (T,U): Bar<Out=V>
+impl<T, U, V> Foo<T> for T
+where
+    (T, U): Bar<Out = V>,
 {
-    //~^^^ ERROR the type parameter `U` is not constrained
-    //~|   ERROR the type parameter `V` is not constrained
+    //~^^^^ ERROR the type parameter `U` is not constrained
+    //~| ERROR the type parameter `V` is not constrained
+    //~| ERROR conflicting implementations of trait `Foo<[isize; 0]>` for type `[isize; 0]`
 
     // Here, `V` is bound by an output type parameter, but the inputs
     // are not themselves constrained.
 }
 
-impl<T,U,V> Foo<(T,U)> for T
-    where (T,U): Bar<Out=V>
+impl<T, U, V> Foo<(T, U)> for T
+where
+    (T, U): Bar<Out = V>,
 {
+    //~^^^^ ERROR conflicting implementations of trait `Foo<([isize; 0], _)>` for type `[isize; 0]`
     // As above, but both T and U ARE constrained.
 }
 
-fn main() { }
+fn main() {}