Auto merge of #130249 - compiler-errors:sad-new-solver-coherence, r=lcnr

Revert "Stabilize `-Znext-solver=coherence`"

This is a clean revert of #121848, prepared by running:

```
$ git revert 17b322fa69 -m1
```

Which effectively reverts:
* a138a92615, 69fdd1457d, d93e047c9f, 1a893ac648

see: https://rust-lang.zulipchat.com/#narrow/stream/364551-t-types.2Ftrait-system-refactor/topic/nalgebra.20hang

Closes #130056

r? lcnr

compiler/rustc_interface/src/tests.rs

@@ -808,7 +808,7 @@ fn test_unstable_options_tracking_hash() {
     tracked!(mir_opt_level, Some(4));
     tracked!(move_size_limit, Some(4096));
     tracked!(mutable_noalias, false);
-    tracked!(next_solver, NextSolverConfig { coherence: true, globally: true });
+    tracked!(next_solver, Some(NextSolverConfig { coherence: true, globally: false }));
     tracked!(no_generate_arange_section, true);
     tracked!(no_jump_tables, true);
     tracked!(no_link, true);

compiler/rustc_middle/src/ty/context.rs

@@ -3132,11 +3132,11 @@ impl<'tcx> TyCtxt<'tcx> {
     }
 
     pub fn next_trait_solver_globally(self) -> bool {
-        self.sess.opts.unstable_opts.next_solver.globally
+        self.sess.opts.unstable_opts.next_solver.map_or(false, |c| c.globally)
     }
 
     pub fn next_trait_solver_in_coherence(self) -> bool {
-        self.sess.opts.unstable_opts.next_solver.coherence
+        self.sess.opts.unstable_opts.next_solver.map_or(false, |c| c.coherence)
     }
 
     pub fn is_impl_trait_in_trait(self, def_id: DefId) -> bool {

compiler/rustc_session/src/config.rs

@@ -842,11 +842,6 @@ pub struct NextSolverConfig {
     /// This is only `true` if `coherence` is also enabled.
     pub globally: bool,
 }
-impl Default for NextSolverConfig {
-    fn default() -> Self {
-        NextSolverConfig { coherence: true, globally: false }
-    }
-}
 
 #[derive(Clone)]
 pub enum Input {

compiler/rustc_session/src/options.rs

@@ -403,7 +403,7 @@ mod desc {
     pub(crate) const parse_unpretty: &str = "`string` or `string=string`";
     pub(crate) const parse_treat_err_as_bug: &str = "either no value or a non-negative number";
     pub(crate) const parse_next_solver_config: &str =
-        "either `globally` (when used without an argument), `coherence` (default) or `no`";
+        "a comma separated list of solver configurations: `globally` (default), and `coherence`";
     pub(crate) const parse_lto: &str =
         "either a boolean (`yes`, `no`, `on`, `off`, etc), `thin`, `fat`, or omitted";
     pub(crate) const parse_linker_plugin_lto: &str =
@@ -1105,16 +1105,27 @@ mod parse {
         }
     }
 
-    pub(crate) fn parse_next_solver_config(slot: &mut NextSolverConfig, v: Option<&str>) -> bool {
+    pub(crate) fn parse_next_solver_config(
+        slot: &mut Option<NextSolverConfig>,
+        v: Option<&str>,
+    ) -> bool {
         if let Some(config) = v {
-            *slot = match config {
-                "no" => NextSolverConfig { coherence: false, globally: false },
-                "coherence" => NextSolverConfig { coherence: true, globally: false },
-                "globally" => NextSolverConfig { coherence: true, globally: true },
+            let mut coherence = false;
+            let mut globally = true;
+            for c in config.split(',') {
+                match c {
+                    "globally" => globally = true,
+                    "coherence" => {
+                        globally = false;
+                        coherence = true;
+                    }
                     _ => return false,
-            };
+                }
+            }
+
+            *slot = Some(NextSolverConfig { coherence: coherence || globally, globally });
         } else {
-            *slot = NextSolverConfig { coherence: true, globally: true };
+            *slot = Some(NextSolverConfig { coherence: true, globally: true });
         }
 
         true
@@ -1867,7 +1878,7 @@ 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: NextSolverConfig = (NextSolverConfig::default(), parse_next_solver_config, [TRACKED],
+    next_solver: Option<NextSolverConfig> = (None, 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)"),

compiler/rustc_trait_selection/src/traits/engine.rs

@@ -35,8 +35,10 @@ where
         if infcx.next_trait_solver() {
             Box::new(NextFulfillmentCtxt::new(infcx))
         } else {
+            let new_solver_globally =
+                infcx.tcx.sess.opts.unstable_opts.next_solver.map_or(false, |c| c.globally);
             assert!(
-                !infcx.tcx.next_trait_solver_globally(),
+                !new_solver_globally,
                 "using old solver even though new solver is enabled globally"
             );
             Box::new(FulfillmentContext::new(infcx))

tests/crashes/118987-2.rs

@@ -1,4 +1,4 @@
-// regression test for #118987
+//@ known-bug: #118987
 #![feature(specialization)] //~ WARN the feature `specialization` is incomplete
 
 trait Assoc {
@@ -15,5 +15,3 @@ trait Foo {}
 
 impl Foo for <u8 as Assoc>::Output {}
 impl Foo for <u16 as Assoc>::Output {}
-//~^ ERROR the trait bound `u16: Assoc` is not satisfied
-fn main() {}

tests/crashes/118987.rs

@@ -0,0 +1,17 @@
+//@ known-bug: #118987
+#![feature(specialization)] //~ WARN the feature `specialization` is incomplete
+
+trait Assoc {
+    type Output;
+}
+
+default impl<T: Clone> Assoc for T {
+    type Output = bool;
+}
+
+impl Assoc for u8 {}
+
+trait Foo {}
+
+impl Foo for <u8 as Assoc>::Output {}
+impl Foo for <u16 as Assoc>::Output {}

tests/crashes/124207.rs

@@ -1,11 +1,9 @@
+//@ known-bug: #124207
 #![feature(transmutability)]
 #![feature(type_alias_impl_trait)]
 trait OpaqueTrait {}
 type OpaqueType = impl OpaqueTrait;
-//~^ ERROR unconstrained opaque type
 trait AnotherTrait {}
 impl<T: std::mem::TransmuteFrom<(), ()>> AnotherTrait for T {}
-//~^ ERROR type provided when a constant was expected
 impl AnotherTrait for OpaqueType {}
-//~^ ERROR conflicting implementations of trait `AnotherTrait`
 pub fn main() {}

tests/crashes/74299.rs

@@ -1,5 +1,5 @@
-// regression test for #73299.
-#![feature(specialization)] //~ WARN the feature `specialization` is incomplete
+//@ known-bug: #74299
+#![feature(specialization)]
 
 trait X {
     type U;
@@ -18,7 +18,6 @@ trait Y {
 
 impl Y for <() as X>::U {}
 impl Y for <i32 as X>::U {}
-//~^ ERROR conflicting implementations of trait `Y` for type `<() as X>::U`
 
 fn main() {
     ().f().g();

tests/ui/associated-types/associated-types-coherence-failure.stderr

@@ -1,20 +1,20 @@
-error[E0119]: conflicting implementations of trait `IntoCow<'_, _>` for type `<_ as ToOwned>::Owned`
+error[E0119]: conflicting implementations of trait `IntoCow<'_, _>` for type `Cow<'_, _>`
   --> $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 `<_ as ToOwned>::Owned`
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `Cow<'_, _>`
 
-error[E0119]: conflicting implementations of trait `IntoCow<'_, _>` for type `<_ as ToOwned>::Owned`
+error[E0119]: conflicting implementations of trait `IntoCow<'_, _>` for type `&_`
   --> $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 `<_ as ToOwned>::Owned`
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `&_`
 
 error: aborting due to 2 previous errors
 

tests/ui/auto-traits/opaque_type_candidate_selection.rs

@@ -0,0 +1,30 @@
+//! used to ICE: #119272
+
+//@ check-pass
+
+#![feature(type_alias_impl_trait)]
+mod defining_scope {
+    use super::*;
+    pub type Alias<T> = impl Sized;
+
+    pub fn cast<T>(x: Container<Alias<T>, T>) -> Container<T, T> {
+        x
+    }
+}
+
+struct Container<T: Trait<U>, U> {
+    x: <T as Trait<U>>::Assoc,
+}
+
+trait Trait<T> {
+    type Assoc;
+}
+
+impl<T> Trait<T> for T {
+    type Assoc = Box<u32>;
+}
+impl<T> Trait<T> for defining_scope::Alias<T> {
+    type Assoc = usize;
+}
+
+fn main() {}

tests/ui/coherence/coherence-negative-outlives-lifetimes.stock.stderr

@@ -5,8 +5,6 @@ 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
 

tests/ui/coherence/coherence-negative-outlives-lifetimes.with_negative_coherence.stderr

@@ -5,8 +5,6 @@ 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
 

tests/ui/coherence/coherence-overlap-downstream-inherent.next.stderr

@@ -1,5 +1,5 @@
 error[E0592]: duplicate definitions with name `dummy`
-  --> $DIR/coherence-overlap-downstream-inherent.rs:7:26
+  --> $DIR/coherence-overlap-downstream-inherent.rs:10:26
    |
 LL | impl<T:Sugar> Sweet<T> { fn dummy(&self) { } }
    |                          ^^^^^^^^^^^^^^^ duplicate definitions for `dummy`
@@ -8,7 +8,7 @@ LL | impl<T:Fruit> Sweet<T> { fn dummy(&self) { } }
    |                          --------------- other definition for `dummy`
 
 error[E0592]: duplicate definitions with name `f`
-  --> $DIR/coherence-overlap-downstream-inherent.rs:13:38
+  --> $DIR/coherence-overlap-downstream-inherent.rs:16:38
    |
 LL | impl<X, T> A<T, X> where T: Bar<X> { fn f(&self) {} }
    |                                      ^^^^^^^^^^^ duplicate definitions for `f`

tests/ui/coherence/coherence-overlap-downstream-inherent.old.stderr

@@ -0,0 +1,23 @@
+error[E0592]: duplicate definitions with name `dummy`
+  --> $DIR/coherence-overlap-downstream-inherent.rs:10:26
+   |
+LL | impl<T:Sugar> Sweet<T> { fn dummy(&self) { } }
+   |                          ^^^^^^^^^^^^^^^ duplicate definitions for `dummy`
+LL |
+LL | impl<T:Fruit> Sweet<T> { fn dummy(&self) { } }
+   |                          --------------- other definition for `dummy`
+
+error[E0592]: duplicate definitions with name `f`
+  --> $DIR/coherence-overlap-downstream-inherent.rs:16:38
+   |
+LL | impl<X, T> A<T, X> where T: Bar<X> { fn f(&self) {} }
+   |                                      ^^^^^^^^^^^ duplicate definitions for `f`
+LL |
+LL | impl<X> A<i32, X> { fn f(&self) {} }
+   |                     ----------- other definition for `f`
+   |
+   = note: downstream crates may implement trait `Bar<_>` for type `i32`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0592`.

tests/ui/coherence/coherence-overlap-downstream-inherent.rs

@@ -1,3 +1,6 @@
+//@ revisions: old next
+//@[next] compile-flags: -Znext-solver
+
 // Tests that we consider `T: Sugar + Fruit` to be ambiguous, even
 // though no impls are found.
 

tests/ui/coherence/coherence-overlap-downstream.next.stderr

@@ -1,5 +1,5 @@
 error[E0119]: conflicting implementations of trait `Sweet`
-  --> $DIR/coherence-overlap-downstream.rs:8:1
+  --> $DIR/coherence-overlap-downstream.rs:11:1
    |
 LL | impl<T:Sugar> Sweet for T { }
    | ------------------------- first implementation here
@@ -7,7 +7,7 @@ LL | impl<T:Fruit> Sweet for T { }
    | ^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation
 
 error[E0119]: conflicting implementations of trait `Foo<_>` for type `i32`
-  --> $DIR/coherence-overlap-downstream.rs:14:1
+  --> $DIR/coherence-overlap-downstream.rs:17:1
    |
 LL | impl<X, T> Foo<X> for T where T: Bar<X> {}
    | --------------------------------------- first implementation here

tests/ui/coherence/coherence-overlap-downstream.old.stderr

@@ -0,0 +1,21 @@
+error[E0119]: conflicting implementations of trait `Sweet`
+  --> $DIR/coherence-overlap-downstream.rs:11:1
+   |
+LL | impl<T:Sugar> Sweet for T { }
+   | ------------------------- first implementation here
+LL | impl<T:Fruit> Sweet for T { }
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation
+
+error[E0119]: conflicting implementations of trait `Foo<_>` for type `i32`
+  --> $DIR/coherence-overlap-downstream.rs:17:1
+   |
+LL | impl<X, T> Foo<X> for T where T: Bar<X> {}
+   | --------------------------------------- first implementation here
+LL | impl<X> Foo<X> for i32 {}
+   | ^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `i32`
+   |
+   = note: downstream crates may implement trait `Bar<_>` for type `i32`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0119`.

tests/ui/coherence/coherence-overlap-downstream.rs

@@ -1,3 +1,6 @@
+//@ revisions: old next
+//@[next] compile-flags: -Znext-solver
+
 // Tests that we consider `T: Sugar + Fruit` to be ambiguous, even
 // though no impls are found.
 

tests/ui/coherence/coherence-overlap-issue-23516-inherent.next.stderr

@@ -1,5 +1,5 @@
 error[E0592]: duplicate definitions with name `dummy`
-  --> $DIR/coherence-overlap-issue-23516-inherent.rs:9:25
+  --> $DIR/coherence-overlap-issue-23516-inherent.rs:12:25
    |
 LL | impl<T:Sugar> Cake<T> { fn dummy(&self) { } }
    |                         ^^^^^^^^^^^^^^^ duplicate definitions for `dummy`

tests/ui/coherence/coherence-overlap-issue-23516-inherent.old.stderr

@@ -0,0 +1,14 @@
+error[E0592]: duplicate definitions with name `dummy`
+  --> $DIR/coherence-overlap-issue-23516-inherent.rs:12:25
+   |
+LL | impl<T:Sugar> Cake<T> { fn dummy(&self) { } }
+   |                         ^^^^^^^^^^^^^^^ duplicate definitions for `dummy`
+LL |
+LL | impl<U:Sugar> Cake<Box<U>> { fn dummy(&self) { } }
+   |                              --------------- other definition for `dummy`
+   |
+   = note: downstream crates may implement trait `Sugar` for type `std::boxed::Box<_>`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0592`.

tests/ui/coherence/coherence-overlap-issue-23516-inherent.rs

@@ -1,3 +1,6 @@
+//@ revisions: old next
+//@[next] compile-flags: -Znext-solver
+
 // Tests that we consider `Box<U>: !Sugar` to be ambiguous, even
 // though we see no impl of `Sugar` for `Box`. Therefore, an overlap
 // error is reported for the following pair of impls (#23516).

tests/ui/coherence/coherence-overlap-issue-23516.next.stderr

@@ -1,5 +1,5 @@
 error[E0119]: conflicting implementations of trait `Sweet` for type `Box<_>`
-  --> $DIR/coherence-overlap-issue-23516.rs:8:1
+  --> $DIR/coherence-overlap-issue-23516.rs:11:1
    |
 LL | impl<T:Sugar> Sweet for T { }
    | ------------------------- first implementation here

tests/ui/coherence/coherence-overlap-issue-23516.old.stderr

@@ -0,0 +1,13 @@
+error[E0119]: conflicting implementations of trait `Sweet` for type `Box<_>`
+  --> $DIR/coherence-overlap-issue-23516.rs:11:1
+   |
+LL | impl<T:Sugar> Sweet for T { }
+   | ------------------------- first implementation here
+LL | impl<U:Sugar> Sweet for Box<U> { }
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `Box<_>`
+   |
+   = note: downstream crates may implement trait `Sugar` for type `std::boxed::Box<_>`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0119`.

tests/ui/coherence/coherence-overlap-issue-23516.rs

@@ -1,3 +1,6 @@
+//@ revisions: old next
+//@[next] compile-flags: -Znext-solver
+
 // Tests that we consider `Box<U>: !Sugar` to be ambiguous, even
 // though we see no impl of `Sugar` for `Box`. Therefore, an overlap
 // error is reported for the following pair of impls (#23516).

tests/ui/coherence/coherence-overlap-negate-not-use-feature-gate.stderr

@@ -5,8 +5,6 @@ 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
 

tests/ui/coherence/coherence-overlap-unnormalizable-projection-0.classic.stderr

@@ -0,0 +1,19 @@
+error[E0119]: conflicting implementations of trait `Trait` for type `Box<_>`
+  --> $DIR/coherence-overlap-unnormalizable-projection-0.rs:27:1
+   |
+LL | / impl<T> Trait for T
+LL | | where
+LL | |     T: 'static,
+LL | |     for<'a> T: WithAssoc<'a>,
+LL | |     for<'a> <T as WithAssoc<'a>>::Assoc: WhereBound,
+   | |____________________________________________________- first implementation here
+...
+LL |   impl<T> Trait for Box<T> {}
+   |   ^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `Box<_>`
+   |
+   = note: downstream crates may implement trait `WithAssoc<'a>` for type `std::boxed::Box<_>`
+   = note: downstream crates may implement trait `WhereBound` for type `<std::boxed::Box<_> as WithAssoc<'a>>::Assoc`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0119`.

tests/ui/coherence/coherence-overlap-unnormalizable-projection-0.next.stderr

@@ -1,5 +1,5 @@
 error[E0119]: conflicting implementations of trait `Trait` for type `Box<_>`
-  --> $DIR/coherence-overlap-unnormalizable-projection-0.rs:24:1
+  --> $DIR/coherence-overlap-unnormalizable-projection-0.rs:27:1
    |
 LL | / impl<T> Trait for T
 LL | | where

tests/ui/coherence/coherence-overlap-unnormalizable-projection-0.rs

@@ -2,6 +2,9 @@
 // "Coherence incorrectly considers `unnormalizable_projection: Trait` to not hold even if it could"
 #![crate_type = "lib"]
 
+//@ revisions: classic next
+//@[next] compile-flags: -Znext-solver
+
 trait WhereBound {}
 impl WhereBound for () {}
 

tests/ui/coherence/coherence-overlap-unnormalizable-projection-1.classic.stderr

@@ -0,0 +1,19 @@
+error[E0119]: conflicting implementations of trait `Trait` for type `Box<_>`
+  --> $DIR/coherence-overlap-unnormalizable-projection-1.rs:26:1
+   |
+LL | / impl<T> Trait for T
+LL | | where
+LL | |     T: 'static,
+LL | |     for<'a> T: WithAssoc<'a>,
+LL | |     for<'a> Box<<T as WithAssoc<'a>>::Assoc>: WhereBound,
+   | |_________________________________________________________- first implementation here
+...
+LL |   impl<T> Trait for Box<T> {}
+   |   ^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `Box<_>`
+   |
+   = note: downstream crates may implement trait `WithAssoc<'a>` for type `std::boxed::Box<_>`
+   = note: downstream crates may implement trait `WhereBound` for type `std::boxed::Box<<std::boxed::Box<_> as WithAssoc<'a>>::Assoc>`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0119`.

tests/ui/coherence/coherence-overlap-unnormalizable-projection-1.next.stderr

@@ -1,5 +1,5 @@
 error[E0119]: conflicting implementations of trait `Trait` for type `Box<_>`
-  --> $DIR/coherence-overlap-unnormalizable-projection-1.rs:23:1
+  --> $DIR/coherence-overlap-unnormalizable-projection-1.rs:26:1
    |
 LL | / impl<T> Trait for T
 LL | | where

tests/ui/coherence/coherence-overlap-unnormalizable-projection-1.rs

@@ -2,6 +2,9 @@
 // "Coherence incorrectly considers `unnormalizable_projection: Trait` to not hold even if it could"
 #![crate_type = "lib"]
 
+//@ revisions: classic next
+//@[next] compile-flags: -Znext-solver
+
 pub trait WhereBound {}
 impl WhereBound for () {}
 

tests/ui/coherence/coherent-due-to-fulfill.rs

@@ -1,4 +1,6 @@
+//@ compile-flags: -Znext-solver=coherence
 //@ check-pass
+
 trait Mirror {
     type Assoc;
 }

tests/ui/coherence/incoherent-even-though-we-fulfill.rs

@@ -1,3 +1,5 @@
+//@ compile-flags: -Znext-solver=coherence
+
 trait Mirror {
     type Assoc;
 }

tests/ui/coherence/incoherent-even-though-we-fulfill.stderr

@@ -1,5 +1,5 @@
 error[E0119]: conflicting implementations of trait `Foo` for type `()`
-  --> $DIR/incoherent-even-though-we-fulfill.rs:15:1
+  --> $DIR/incoherent-even-though-we-fulfill.rs:17:1
    |
 LL | impl<T> Foo for T where (): Mirror<Assoc = T> {}
    | --------------------------------------------- first implementation here

tests/ui/coherence/inter-crate-ambiguity-causes-notes.next.stderr

@@ -1,5 +1,5 @@
 error[E0119]: conflicting implementations of trait `From<()>` for type `S`
-  --> $DIR/inter-crate-ambiguity-causes-notes.rs:9:1
+  --> $DIR/inter-crate-ambiguity-causes-notes.rs:12:1
    |
 LL |   impl From<()> for S {
    |   ------------------- first implementation here

tests/ui/coherence/inter-crate-ambiguity-causes-notes.old.stderr

@@ -0,0 +1,17 @@
+error[E0119]: conflicting implementations of trait `From<()>` for type `S`
+  --> $DIR/inter-crate-ambiguity-causes-notes.rs:12:1
+   |
+LL |   impl From<()> for S {
+   |   ------------------- first implementation here
+...
+LL | / impl<I> From<I> for S
+LL | |
+LL | | where
+LL | |     I: Iterator<Item = ()>,
+   | |___________________________^ conflicting implementation for `S`
+   |
+   = note: upstream crates may add a new impl of trait `std::iter::Iterator` for type `()` in future versions
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0119`.

tests/ui/coherence/inter-crate-ambiguity-causes-notes.rs

@@ -1,3 +1,6 @@
+//@ revisions: old next
+//@[next] compile-flags: -Znext-solver
+
 struct S;
 
 impl From<()> for S {

tests/ui/coherence/negative-coherence-check-placeholder-outlives.stderr

@@ -5,8 +5,6 @@ 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
 

tests/ui/coherence/negative-coherence-considering-regions.any_lt.stderr

@@ -6,8 +6,6 @@ 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
 

tests/ui/coherence/negative-coherence-placeholder-region-constraints-on-unification.explicit.stderr

@@ -8,7 +8,6 @@ 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

tests/ui/coherence/normalize-for-errors.current.stderr

@@ -0,0 +1,14 @@
+error[E0119]: conflicting implementations of trait `MyTrait<_>` for type `(Box<(MyType,)>, _)`
+  --> $DIR/normalize-for-errors.rs:17:1
+   |
+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,)>, _)`
+   |
+   = note: upstream crates may add a new impl of trait `std::marker::Copy` for type `std::boxed::Box<(MyType,)>` in future versions
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0119`.

tests/ui/coherence/normalize-for-errors.next.stderr

@@ -1,5 +1,5 @@
 error[E0119]: conflicting implementations of trait `MyTrait<_>` for type `(Box<(MyType,)>, <_ as Iterator>::Item)`
-  --> $DIR/normalize-for-errors.rs:13:1
+  --> $DIR/normalize-for-errors.rs:17:1
    |
 LL | impl<T: Copy, S: Iterator> MyTrait<S> for (T, S::Item) {}
    | ------------------------------------------------------ first implementation here

tests/ui/coherence/normalize-for-errors.rs

@@ -1,3 +1,7 @@
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
+
 struct MyType;
 trait MyTrait<S> {}
 
@@ -14,6 +18,6 @@ impl<S: Iterator> MyTrait<S> for (Box<<(MyType,) as Mirror>::Assoc>, S::Item) {}
 //~^ ERROR conflicting implementations of trait `MyTrait<_>` for type `(Box<(MyType,)>,
 //~| NOTE conflicting implementation for `(Box<(MyType,)>,
 //~| NOTE upstream crates may add a new impl of trait `std::marker::Copy` for type `std::boxed::Box<(MyType,)>` in future versions
-//~| NOTE upstream crates may add a new impl of trait `std::clone::Clone` for type `std::boxed::Box<(MyType,)>` in future versions
+//[next]~| NOTE upstream crates may add a new impl of trait `std::clone::Clone` for type `std::boxed::Box<(MyType,)>` in future versions
 
 fn main() {}

tests/ui/coherence/occurs-check/associated-type.next.stderr

@@ -3,7 +3,7 @@
  WARN rustc_infer::infer::relate::generalize may incompletely handle alias type: AliasTy { args: [*const ?1t, '^0.Named(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, '^0.Named(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 (), ())`
-  --> $DIR/associated-type.rs:32:1
+  --> $DIR/associated-type.rs:31:1
    |
 LL |   impl<T> Overlap<T> for T {
    |   ------------------------ first implementation here
@@ -17,7 +17,7 @@ LL | |     for<'a> *const T: ToUnit<'a>,
    = note: this behavior recently changed as a result of a bug fix; see rust-lang/rust#56105 for details
 
 error[E0284]: type annotations needed: cannot normalize `<for<'a> fn(&'a (), ()) as Overlap<for<'a> fn(&'a (), ())>>::Assoc`
-  --> $DIR/associated-type.rs:45:59
+  --> $DIR/associated-type.rs:44:59
    |
 LL |     foo::<for<'a> fn(&'a (), ()), for<'a> fn(&'a (), ())>(3usize);
    |                                                           ^^^^^^ cannot normalize `<for<'a> fn(&'a (), ()) as Overlap<for<'a> fn(&'a (), ())>>::Assoc`

tests/ui/coherence/occurs-check/associated-type.old.stderr

@@ -1,9 +1,13 @@
  WARN rustc_infer::infer::relate::generalize may incompletely handle alias type: AliasTy { args: [*const ?1t, '^0.Named(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, !2_0.Named(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, '^0.Named(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, !2_0.Named(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, '^0.Named(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, !2_0.Named(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, '^0.Named(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 (), ())`
-  --> $DIR/associated-type.rs:32:1
+ WARN rustc_infer::infer::relate::generalize may incompletely handle alias type: AliasTy { args: [*const ?1t, !2_0.Named(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 (), _)`
+  --> $DIR/associated-type.rs:31:1
    |
 LL |   impl<T> Overlap<T> for T {
    |   ------------------------ first implementation here
@@ -12,7 +16,7 @@ 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
 

tests/ui/coherence/occurs-check/associated-type.rs

@@ -1,5 +1,4 @@
 //@ revisions: old next
-//@ ignore-compare-mode-next-solver (explicit revisions)
 //@[next] compile-flags: -Znext-solver
 
 // A regression test for #105787

tests/ui/coherence/occurs-check/opaques.current.stderr

@@ -1,12 +0,0 @@
-error[E0119]: conflicting implementations of trait `Trait<_>`
-  --> $DIR/opaques.rs:28:1
-   |
-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`.

tests/ui/coherence/occurs-check/opaques.next.stderr

@@ -1,5 +1,5 @@
 error[E0119]: conflicting implementations of trait `Trait<_>`
-  --> $DIR/opaques.rs:28:1
+  --> $DIR/opaques.rs:30:1
    |
 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:11:20
+  --> $DIR/opaques.rs:13:20
    |
 LL |     pub fn cast<T>(x: Container<Alias<T>, T>) -> Container<T, T> {
    |                    ^ cannot infer type

tests/ui/coherence/occurs-check/opaques.rs

@@ -1,8 +1,10 @@
-//@ revisions: current next
-//@ ignore-compare-mode-next-solver (explicit revisions)
+//@revisions: old 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::*;
@@ -26,7 +28,7 @@ impl<T> Trait<T> for T {
     type Assoc = Box<u32>;
 }
 impl<T> Trait<T> for defining_scope::Alias<T> {
-    //~^ ERROR conflicting implementations of trait
+    //[next]~^ ERROR conflicting implementations of trait
     type Assoc = usize;
 }
 

tests/ui/coherence/orphan-check-opaque-types-not-covering.classic.stderr

@@ -1,5 +1,5 @@
 error[E0210]: type parameter `T` must be covered by another type when it appears before the first local type (`Local`)
-  --> $DIR/orphan-check-opaque-types-not-covering.rs:14:6
+  --> $DIR/orphan-check-opaque-types-not-covering.rs:17:6
    |
 LL | impl<T> foreign::Trait0<Local, T, ()> for Identity<T> {}
    |      ^ type parameter `T` must be covered by another type when it appears before the first local type (`Local`)
@@ -8,7 +8,7 @@ LL | impl<T> foreign::Trait0<Local, T, ()> for Identity<T> {}
    = note: in this case, 'before' refers to the following order: `impl<..> ForeignTrait<T1, ..., Tn> for T0`, where `T0` is the first and `Tn` is the last
 
 error[E0210]: type parameter `T` must be covered by another type when it appears before the first local type (`Local`)
-  --> $DIR/orphan-check-opaque-types-not-covering.rs:23:6
+  --> $DIR/orphan-check-opaque-types-not-covering.rs:26:6
    |
 LL | impl<T> foreign::Trait1<Local, T> for Opaque<T> {}
    |      ^ type parameter `T` must be covered by another type when it appears before the first local type (`Local`)

tests/ui/coherence/orphan-check-opaque-types-not-covering.next.stderr

@@ -0,0 +1,21 @@
+error[E0210]: type parameter `T` must be covered by another type when it appears before the first local type (`Local`)
+  --> $DIR/orphan-check-opaque-types-not-covering.rs:17:6
+   |
+LL | impl<T> foreign::Trait0<Local, T, ()> for Identity<T> {}
+   |      ^ type parameter `T` must be covered by another type when it appears before the first local type (`Local`)
+   |
+   = note: implementing a foreign trait is only possible if at least one of the types for which it is implemented is local, and no uncovered type parameters appear before that first local type
+   = note: in this case, 'before' refers to the following order: `impl<..> ForeignTrait<T1, ..., Tn> for T0`, where `T0` is the first and `Tn` is the last
+
+error[E0210]: type parameter `T` must be covered by another type when it appears before the first local type (`Local`)
+  --> $DIR/orphan-check-opaque-types-not-covering.rs:26:6
+   |
+LL | impl<T> foreign::Trait1<Local, T> for Opaque<T> {}
+   |      ^ type parameter `T` must be covered by another type when it appears before the first local type (`Local`)
+   |
+   = note: implementing a foreign trait is only possible if at least one of the types for which it is implemented is local, and no uncovered type parameters appear before that first local type
+   = note: in this case, 'before' refers to the following order: `impl<..> ForeignTrait<T1, ..., Tn> for T0`, where `T0` is the first and `Tn` is the last
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0210`.

tests/ui/coherence/orphan-check-opaque-types-not-covering.rs

@@ -1,5 +1,8 @@
 // Opaque types never cover type parameters.
 
+//@ revisions: classic next
+//@[next] compile-flags: -Znext-solver
+
 //@ aux-crate:foreign=parametrized-trait.rs
 //@ edition:2021
 

tests/ui/coherence/orphan-check-projections-covering.rs

@@ -5,6 +5,9 @@
 // first which would've lead to real-word regressions.
 
 //@ check-pass
+//@ revisions: classic next
+//@[next] compile-flags: -Znext-solver
+
 //@ aux-crate:foreign=parametrized-trait.rs
 //@ edition:2021
 

tests/ui/coherence/orphan-check-weak-aliases-not-covering.classic.stderr

@@ -1,5 +1,5 @@
 error[E0210]: type parameter `T` must be covered by another type when it appears before the first local type (`Local`)
-  --> $DIR/orphan-check-weak-aliases-not-covering.rs:13:6
+  --> $DIR/orphan-check-weak-aliases-not-covering.rs:16:6
    |
 LL | impl<T> foreign::Trait1<Local, T> for Identity<T> {}
    |      ^ type parameter `T` must be covered by another type when it appears before the first local type (`Local`)

tests/ui/coherence/orphan-check-weak-aliases-not-covering.next.stderr

@@ -0,0 +1,12 @@
+error[E0210]: type parameter `T` must be covered by another type when it appears before the first local type (`Local`)
+  --> $DIR/orphan-check-weak-aliases-not-covering.rs:16:6
+   |
+LL | impl<T> foreign::Trait1<Local, T> for Identity<T> {}
+   |      ^ type parameter `T` must be covered by another type when it appears before the first local type (`Local`)
+   |
+   = note: implementing a foreign trait is only possible if at least one of the types for which it is implemented is local, and no uncovered type parameters appear before that first local type
+   = note: in this case, 'before' refers to the following order: `impl<..> ForeignTrait<T1, ..., Tn> for T0`, where `T0` is the first and `Tn` is the last
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0210`.

tests/ui/coherence/orphan-check-weak-aliases-not-covering.rs

@@ -1,5 +1,8 @@
 // Weak aliases might not cover type parameters.
 
+//@ revisions: classic next
+//@[next] compile-flags: -Znext-solver
+
 //@ aux-crate:foreign=parametrized-trait.rs
 //@ edition:2021
 

tests/ui/coherence/skip-reporting-if-references-err.current.stderr

@@ -0,0 +1,27 @@
+error[E0726]: implicit elided lifetime not allowed here
+  --> $DIR/skip-reporting-if-references-err.rs:10:9
+   |
+LL | impl<T> ToUnit for T {}
+   |         ^^^^^^ expected lifetime parameter
+   |
+help: indicate the anonymous lifetime
+   |
+LL | impl<T> ToUnit<'_> for T {}
+   |               ++++
+
+error[E0277]: the trait bound `for<'a> (): ToUnit<'a>` is not satisfied
+  --> $DIR/skip-reporting-if-references-err.rs:15:29
+   |
+LL | impl Overlap for for<'a> fn(<() as ToUnit<'a>>::Unit) {}
+   |                             ^^^^^^^^^^^^^^^^^^^^^^^^ the trait `for<'a> ToUnit<'a>` is not implemented for `()`
+
+error[E0277]: the trait bound `for<'a> (): ToUnit<'a>` is not satisfied
+  --> $DIR/skip-reporting-if-references-err.rs:15:18
+   |
+LL | impl Overlap for for<'a> fn(<() as ToUnit<'a>>::Unit) {}
+   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `for<'a> ToUnit<'a>` is not implemented for `()`
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0277, E0726.
+For more information about an error, try `rustc --explain E0277`.

tests/ui/coherence/skip-reporting-if-references-err.next.stderr

@@ -1,5 +1,5 @@
 error[E0726]: implicit elided lifetime not allowed here
-  --> $DIR/skip-reporting-if-references-err.rs:6:9
+  --> $DIR/skip-reporting-if-references-err.rs:10:9
    |
 LL | impl<T> ToUnit for T {}
    |         ^^^^^^ expected lifetime parameter

tests/ui/coherence/skip-reporting-if-references-err.rs

@@ -1,4 +1,8 @@
 // Regression test for #121006.
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
+
 trait ToUnit<'a> {
     type Unit;
 }
@@ -9,5 +13,7 @@ impl<T> ToUnit for T {}
 trait Overlap {}
 impl<U> Overlap for fn(U) {}
 impl Overlap for for<'a> fn(<() as ToUnit<'a>>::Unit) {}
+//[current]~^ ERROR the trait bound `for<'a> (): ToUnit<'a>` is not satisfied
+//[current]~| ERROR the trait bound `for<'a> (): ToUnit<'a>` is not satisfied
 
 fn main() {}

tests/ui/coherence/super-traits/super-trait-knowable-1.current.stderr

@@ -0,0 +1,13 @@
+error[E0119]: conflicting implementations of trait `Overlap<_>` for type `()`
+  --> $DIR/super-trait-knowable-1.rs:16:1
+   |
+LL | impl<T, U: Sub<T>> Overlap<T> for U {}
+   | ----------------------------------- first implementation here
+LL | impl<T> Overlap<T> for () {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `()`
+   |
+   = note: downstream crates may implement trait `Sub<_>` for type `()`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0119`.

tests/ui/coherence/super-traits/super-trait-knowable-1.rs

@@ -3,7 +3,10 @@
 // We therefore elaborate super trait bounds in the implicit negative
 // overlap check.
 
-//@ check-pass
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
+//@[next] check-pass
 
 trait Super {}
 trait Sub<T>: Super {}
@@ -11,5 +14,6 @@ trait Sub<T>: Super {}
 trait Overlap<T> {}
 impl<T, U: Sub<T>> Overlap<T> for U {}
 impl<T> Overlap<T> for () {}
+//[current]~^ ERROR conflicting implementations
 
 fn main() {}

tests/ui/coherence/super-traits/super-trait-knowable-2.rs

@@ -9,6 +9,9 @@
 // which caused the old solver to emit a `Tensor: TensorValue` goal in
 // `fn normalize_to_error` which then failed, causing this test to pass.
 
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
 //@ check-pass
 
 pub trait TensorValue {

tests/ui/coherence/super-traits/super-trait-knowable-3.current.stderr

@@ -0,0 +1,13 @@
+error[E0119]: conflicting implementations of trait `Overlap<_>` for type `()`
+  --> $DIR/super-trait-knowable-3.rs:19:1
+   |
+LL | impl<T, U: Bound<W<T>>> Overlap<T> for U {}
+   | ---------------------------------------- first implementation here
+LL | impl<T> Overlap<T> for () {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `()`
+   |
+   = note: downstream crates may implement trait `Sub<_>` for type `()`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0119`.

tests/ui/coherence/super-traits/super-trait-knowable-3.rs

@@ -2,7 +2,10 @@
 // super trait bound is in a nested goal so this would not
 // compile if we were to only elaborate root goals.
 
-//@ check-pass
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
+//@[next] check-pass
 
 trait Super {}
 trait Sub<T>: Super {}
@@ -14,5 +17,6 @@ impl<T: Sub<U>, U> Bound<W<U>> for T {}
 trait Overlap<T> {}
 impl<T, U: Bound<W<T>>> Overlap<T> for U {}
 impl<T> Overlap<T> for () {}
+//[current]~^ ERROR conflicting implementations of trait `Overlap<_>` for type `()`
 
 fn main() {}

tests/ui/const-generics/generic_const_exprs/unevaluated-const-ice-119731.rs

@@ -22,7 +22,6 @@ mod v20 {
     impl v17<512, v0> {
         pub const fn v21() -> v18 {}
         //~^ ERROR cannot find type `v18` in this scope
-        //~| ERROR duplicate definitions with name `v21`
     }
 
     impl<const v10: usize> v17<v10, v2> {

tests/ui/const-generics/generic_const_exprs/unevaluated-const-ice-119731.stderr

@@ -1,5 +1,5 @@
 error[E0432]: unresolved import `v20::v13`
-  --> $DIR/unevaluated-const-ice-119731.rs:38:15
+  --> $DIR/unevaluated-const-ice-119731.rs:37:15
    |
 LL | pub use v20::{v13, v17};
    |               ^^^
@@ -23,7 +23,7 @@ LL |         pub const fn v21() -> v18 {}
    |                               ^^^ help: a type alias with a similar name exists: `v11`
 
 error[E0412]: cannot find type `v18` in this scope
-  --> $DIR/unevaluated-const-ice-119731.rs:31:31
+  --> $DIR/unevaluated-const-ice-119731.rs:30:31
    |
 LL |     pub type v11 = [[usize; v4]; v4];
    |     --------------------------------- similarly named type alias `v11` defined here
@@ -32,7 +32,7 @@ LL |         pub const fn v21() -> v18 {
    |                               ^^^ help: a type alias with a similar name exists: `v11`
 
 error[E0422]: cannot find struct, variant or union type `v18` in this scope
-  --> $DIR/unevaluated-const-ice-119731.rs:33:13
+  --> $DIR/unevaluated-const-ice-119731.rs:32:13
    |
 LL |     pub type v11 = [[usize; v4]; v4];
    |     --------------------------------- similarly named type alias `v11` defined here
@@ -73,29 +73,20 @@ LL + #![feature(adt_const_params)]
    |
 
 error: maximum number of nodes exceeded in constant v20::v17::<v10, v2>::{constant#1}
-  --> $DIR/unevaluated-const-ice-119731.rs:28:37
+  --> $DIR/unevaluated-const-ice-119731.rs:27:37
    |
 LL |     impl<const v10: usize> v17<v10, v2> {
    |                                     ^^
 
 error: maximum number of nodes exceeded in constant v20::v17::<v10, v2>::{constant#1}
-  --> $DIR/unevaluated-const-ice-119731.rs:28:37
+  --> $DIR/unevaluated-const-ice-119731.rs:27:37
    |
 LL |     impl<const v10: usize> v17<v10, v2> {
    |                                     ^^
    |
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
-error[E0592]: duplicate definitions with name `v21`
-  --> $DIR/unevaluated-const-ice-119731.rs:23:9
-   |
-LL |         pub const fn v21() -> v18 {}
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^ duplicate definitions for `v21`
-...
-LL |         pub const fn v21() -> v18 {
-   |         ------------------------- other definition for `v21`
+error: aborting due to 9 previous errors; 2 warnings emitted
 
-error: aborting due to 10 previous errors; 2 warnings emitted
-
-Some errors have detailed explanations: E0412, E0422, E0425, E0432, E0592.
+Some errors have detailed explanations: E0412, E0422, E0425, E0432.
 For more information about an error, try `rustc --explain E0412`.

tests/ui/const-generics/generic_const_exprs/unknown-alias-defkind-anonconst-ice-116710.rs

@@ -10,5 +10,6 @@ trait Trait {}
 impl<const N: u32> Trait for A<N> {}
 
 impl<const N: u32> Trait for A<N> {}
+//~^ ERROR conflicting implementations of trait `Trait` for type `A<_>`
 
 pub fn main() {}

tests/ui/const-generics/generic_const_exprs/unknown-alias-defkind-anonconst-ice-116710.stderr

@@ -4,6 +4,16 @@ error[E0423]: expected value, found builtin type `u8`
 LL | struct A<const N: u32 = 1, const M: u32 = u8>;
    |                                           ^^ not a value
 
-error: aborting due to 1 previous error
+error[E0119]: conflicting implementations of trait `Trait` for type `A<_>`
+  --> $DIR/unknown-alias-defkind-anonconst-ice-116710.rs:12:1
+   |
+LL | impl<const N: u32> Trait for A<N> {}
+   | --------------------------------- first implementation here
+LL |
+LL | impl<const N: u32> Trait for A<N> {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `A<_>`
 
-For more information about this error, try `rustc --explain E0423`.
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0119, E0423.
+For more information about an error, try `rustc --explain E0119`.

tests/ui/error-codes/e0119/issue-23563.stderr

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

tests/ui/feature-gates/feature-gate-with_negative_coherence.stderr

@@ -6,8 +6,6 @@ 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
 

tests/ui/higher-ranked/leak-check/leak-check-in-selection-5-ambig.rs

@@ -3,9 +3,9 @@
 //@ check-pass
 
 // The new trait solver does not return region constraints if the goal
-// is still ambiguous. However, the `'!a = 'static` constraint from
-// `(): LeakCheckFailure<'!a, V>`  is also returned via the canonical
-// var values, causing this test to compile.
+// is still ambiguous. This causes the following test to fail with ambiguity,
+// even though `(): LeakCheckFailure<'!a, V>` would return `'!a: 'static`
+// which would have caused a leak check failure.
 
 trait Ambig {}
 impl Ambig for u32 {}

tests/ui/higher-ranked/structually-relate-aliases.rs

@@ -11,6 +11,7 @@ type Assoc<'a, T> = <T as ToUnit<'a>>::Unit;
 impl<T> Overlap<T> for T {}
 
 impl<T> Overlap<for<'a> fn(&'a (), Assoc<'a, T>)> for T {}
-//~^ ERROR conflicting implementations of trait `Overlap<for<'a> fn(&'a (), _)>`
+//~^ ERROR 13:17: 13:49: the trait bound `for<'a> T: ToUnit<'a>` is not satisfied [E0277]
+//~| ERROR 13:36: 13:48: the trait bound `for<'a> T: ToUnit<'a>` is not satisfied [E0277]
 
 fn main() {}

tests/ui/higher-ranked/structually-relate-aliases.stderr

@@ -1,18 +1,27 @@
  WARN rustc_infer::infer::relate::generalize may incompletely handle alias type: AliasTy { args: [?1t, '^0.Named(DefId(0:15 ~ structually_relate_aliases[de75]::{impl#1}::'a), "'a")], def_id: DefId(0:5 ~ structually_relate_aliases[de75]::ToUnit::Unit), .. }
- WARN rustc_infer::infer::relate::generalize may incompletely handle alias type: AliasTy { args: [?1t, '^0.Named(DefId(0:15 ~ structually_relate_aliases[de75]::{impl#1}::'a), "'a")], def_id: DefId(0:5 ~ structually_relate_aliases[de75]::ToUnit::Unit), .. }
- WARN rustc_infer::infer::relate::generalize may incompletely handle alias type: AliasTy { args: [?1t, '^0.Named(DefId(0:15 ~ structually_relate_aliases[de75]::{impl#1}::'a), "'a")], def_id: DefId(0:5 ~ structually_relate_aliases[de75]::ToUnit::Unit), .. }
- WARN rustc_infer::infer::relate::generalize may incompletely handle alias type: AliasTy { args: [?1t, '^0.Named(DefId(0:15 ~ structually_relate_aliases[de75]::{impl#1}::'a), "'a")], def_id: DefId(0:5 ~ structually_relate_aliases[de75]::ToUnit::Unit), .. }
-error[E0119]: conflicting implementations of trait `Overlap<for<'a> fn(&'a (), _)>` for type `for<'a> fn(&'a (), _)`
-  --> $DIR/structually-relate-aliases.rs:13:1
+ WARN rustc_infer::infer::relate::generalize may incompletely handle alias type: AliasTy { args: [?1t, !2_0.Named(DefId(0:15 ~ structually_relate_aliases[de75]::{impl#1}::'a), "'a")], def_id: DefId(0:5 ~ structually_relate_aliases[de75]::ToUnit::Unit), .. }
+error[E0277]: the trait bound `for<'a> T: ToUnit<'a>` is not satisfied
+  --> $DIR/structually-relate-aliases.rs:13:36
    |
-LL | impl<T> Overlap<T> for T {}
-   | ------------------------ first implementation here
-LL |
 LL | impl<T> Overlap<for<'a> fn(&'a (), Assoc<'a, T>)> for T {}
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `for<'a> fn(&'a (), _)`
+   |                                    ^^^^^^^^^^^^ the trait `for<'a> ToUnit<'a>` is not implemented for `T`
    |
-   = note: this behavior recently changed as a result of a bug fix; see rust-lang/rust#56105 for details
+help: consider restricting type parameter `T`
+   |
+LL | impl<T: for<'a> ToUnit<'a>> Overlap<for<'a> fn(&'a (), Assoc<'a, T>)> for T {}
+   |       ++++++++++++++++++++
 
-error: aborting due to 1 previous error
+error[E0277]: the trait bound `for<'a> T: ToUnit<'a>` is not satisfied
+  --> $DIR/structually-relate-aliases.rs:13:17
+   |
+LL | impl<T> Overlap<for<'a> fn(&'a (), Assoc<'a, T>)> for T {}
+   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `for<'a> ToUnit<'a>` is not implemented for `T`
+   |
+help: consider restricting type parameter `T`
+   |
+LL | impl<T: for<'a> ToUnit<'a>> Overlap<for<'a> fn(&'a (), Assoc<'a, T>)> for T {}
+   |       ++++++++++++++++++++
 
-For more information about this error, try `rustc --explain E0119`.
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/impl-trait/auto-trait-coherence.old.stderr

@@ -1,11 +1,11 @@
-error[E0119]: conflicting implementations of trait `AnotherTrait` for type `D<_>`
+error[E0119]: conflicting implementations of trait `AnotherTrait` for type `D<OpaqueType>`
   --> $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<_>`
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `D<OpaqueType>`
 
 error: aborting due to 1 previous error
 

tests/ui/impl-trait/auto-trait-coherence.rs

@@ -1,3 +1,6 @@
+//@ 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)]
@@ -19,7 +22,8 @@ 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> {
-    //~^ ERROR conflicting implementations of trait `AnotherTrait` for type `D<_>`
+    //[old]~^ ERROR conflicting implementations of trait `AnotherTrait` for type `D<OpaqueType>`
+    //[next]~^^ ERROR conflicting implementations of trait `AnotherTrait` for type `D<_>`
 }
 
 fn main() {}

tests/ui/impl-trait/auto-trait-coherence.stderr

@@ -1,12 +0,0 @@
-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`.

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<_>` for type `Foo`
+//~^ ERROR conflicting implementations of trait `Into<T>` for type `Foo`
     fn into(self) -> T {
         Foo
     }

tests/ui/impl-trait/coherence-treats-tait-ambig.stderr

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

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<_>`
+    //~^ ERROR conflicting implementations of trait `AnotherTrait` for type `D<OpaqueType>`
 }
 
 fn main() {}

tests/ui/impl-trait/negative-reasoning.stderr

@@ -1,11 +1,13 @@
-error[E0119]: conflicting implementations of trait `AnotherTrait` for type `D<_>`
+error[E0119]: conflicting implementations of trait `AnotherTrait` for type `D<OpaqueType>`
   --> $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<_>`
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `D<OpaqueType>`
+   |
+   = note: upstream crates may add a new impl of trait `std::marker::FnPtr` for type `OpaqueType` in future versions
 
 error: aborting due to 1 previous error
 

tests/ui/impl-unused-tps.rs

@@ -1,3 +1,5 @@
+//~ ERROR overflow evaluating the requirement `([isize; 0], _): Sized
+
 trait Foo<A> {
     fn get(&self, A: &A) { }
 }
@@ -14,10 +16,7 @@ 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.
 }
 
@@ -38,31 +37,26 @@ impl<T, U> Bar for T {
 }
 
 impl<T,U> Bar for T
-where
-    T: Bar<Out = U>,
+    where T : Bar<Out=U>
 {
-    //~^^^^ ERROR the type parameter `U` is not constrained by the impl trait, self type, or predicates
-    //~| ERROR conflicting implementations of trait `Bar`
+    //~^^^ ERROR the type parameter `U` is not constrained
+
     // This crafty self-referential attempt is still no good.
 }
 
 impl<T,U,V> Foo<T> for T
-where
-    (T, U): Bar<Out = V>,
+    where (T,U): Bar<Out=V>
 {
-    //~^^^^ ERROR the type parameter `U` 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>,
+    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.
 }
 

tests/ui/impl-unused-tps.stderr

@@ -1,76 +1,56 @@
 error[E0119]: conflicting implementations of trait `Foo<_>` for type `[isize; 0]`
-  --> $DIR/impl-unused-tps.rs:28:1
+  --> $DIR/impl-unused-tps.rs:27:1
    |
 LL | impl<T> Foo<T> for [isize;0] {
-   | ----------------------------- first implementation here
+   | ---------------------------- first implementation here
 ...
 LL | impl<T,U> Foo<T> for U {
-   | ^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `[isize; 0]`
+   | ^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `[isize; 0]`
 
-error[E0119]: conflicting implementations of trait `Bar`
-  --> $DIR/impl-unused-tps.rs:40:1
+error[E0275]: overflow evaluating the requirement `([isize; 0], _): Sized`
+   |
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`impl_unused_tps`)
+note: required for `([isize; 0], _)` to implement `Bar`
+  --> $DIR/impl-unused-tps.rs:31:11
    |
 LL | impl<T,U> Bar for T {
-   |   -------------------- first implementation here
-...
-LL | / impl<T, U> Bar for T
-LL | | where
-LL | |     T: Bar<Out = U>,
-   | |____________________^ conflicting implementation
-
-error[E0119]: conflicting implementations of trait `Foo<[isize; 0]>` for type `[isize; 0]`
-  --> $DIR/impl-unused-tps.rs:49:1
-   |
-LL |   impl<T> Foo<T> for [isize; 0] {
-   |   ----------------------------- first implementation here
-...
-LL | / impl<T, U, V> Foo<T> for T
-LL | | where
-LL | |     (T, U): Bar<Out = V>,
-   | |_________________________^ conflicting implementation for `[isize; 0]`
-
-error[E0119]: conflicting implementations of trait `Foo<([isize; 0], _)>` for type `[isize; 0]`
-  --> $DIR/impl-unused-tps.rs:61:1
-   |
-LL |   impl<T> Foo<T> for [isize; 0] {
-   |   ----------------------------- first implementation here
-...
-LL | / impl<T, U, V> Foo<(T, U)> for T
-LL | | where
-LL | |     (T, U): Bar<Out = V>,
-   | |_________________________^ conflicting implementation for `[isize; 0]`
+   |      -    ^^^     ^
+   |      |
+   |      unsatisfied trait bound introduced here
+   = note: 126 redundant requirements hidden
+   = note: required for `([isize; 0], _)` to implement `Bar`
 
 error[E0207]: the type parameter `U` is not constrained by the impl trait, self type, or predicates
-  --> $DIR/impl-unused-tps.rs:13:9
+  --> $DIR/impl-unused-tps.rs:15:8
    |
 LL | impl<T,U> Foo<T> for [isize;1] {
    |        ^ unconstrained type parameter
 
 error[E0207]: the type parameter `U` is not constrained by the impl trait, self type, or predicates
-  --> $DIR/impl-unused-tps.rs:32:9
+  --> $DIR/impl-unused-tps.rs:31:8
    |
 LL | impl<T,U> Bar for T {
    |        ^ unconstrained type parameter
 
 error[E0207]: the type parameter `U` is not constrained by the impl trait, self type, or predicates
-  --> $DIR/impl-unused-tps.rs:40:9
+  --> $DIR/impl-unused-tps.rs:39:8
    |
 LL | impl<T,U> Bar for T
    |        ^ unconstrained type parameter
 
 error[E0207]: the type parameter `U` is not constrained by the impl trait, self type, or predicates
-  --> $DIR/impl-unused-tps.rs:49:9
+  --> $DIR/impl-unused-tps.rs:47:8
    |
 LL | impl<T,U,V> Foo<T> for T
    |        ^ unconstrained type parameter
 
 error[E0207]: the type parameter `V` is not constrained by the impl trait, self type, or predicates
-  --> $DIR/impl-unused-tps.rs:49:12
+  --> $DIR/impl-unused-tps.rs:47:10
    |
 LL | impl<T,U,V> Foo<T> for T
    |          ^ unconstrained type parameter
 
-error: aborting due to 9 previous errors
+error: aborting due to 7 previous errors
 
-Some errors have detailed explanations: E0119, E0207.
+Some errors have detailed explanations: E0119, E0207, E0275.
 For more information about an error, try `rustc --explain E0119`.

tests/ui/issues/issue-48728.rs

@@ -1,8 +1,12 @@
 // Regression test for #48728, an ICE that occurred computing
 // coherence "help" information.
 
-//@ check-pass
-#[derive(Clone)]
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
+//@[next] check-pass
+
+#[derive(Clone)] //[current]~ ERROR conflicting implementations of trait `Clone`
 struct Node<T: ?Sized>(Box<T>);
 
 impl<T: Clone + ?Sized> Clone for Node<[T]> {

tests/ui/specialization/coherence/default-impl-normalization-ambig-2.stderr

@@ -1,21 +0,0 @@
-warning: the feature `specialization` is incomplete and may not be safe to use and/or cause compiler crashes
-  --> $DIR/default-impl-normalization-ambig-2.rs:2:12
-   |
-LL | #![feature(specialization)]
-   |            ^^^^^^^^^^^^^^
-   |
-   = note: see issue #31844 <https://github.com/rust-lang/rust/issues/31844> for more information
-   = help: consider using `min_specialization` instead, which is more stable and complete
-   = note: `#[warn(incomplete_features)]` on by default
-
-error[E0277]: the trait bound `u16: Assoc` is not satisfied
-  --> $DIR/default-impl-normalization-ambig-2.rs:17:14
-   |
-LL | impl Foo for <u16 as Assoc>::Output {}
-   |              ^^^^^^^^^^^^^^^^^^^^^^ the trait `Assoc` is not implemented for `u16`
-   |
-   = help: the trait `Assoc` is implemented for `u8`
-
-error: aborting due to 1 previous error; 1 warning emitted
-
-For more information about this error, try `rustc --explain E0277`.

tests/ui/specialization/coherence/default-item-normalization-ambig-1.stderr

@@ -1,21 +0,0 @@
-warning: the feature `specialization` is incomplete and may not be safe to use and/or cause compiler crashes
-  --> $DIR/default-item-normalization-ambig-1.rs:2:12
-   |
-LL | #![feature(specialization)]
-   |            ^^^^^^^^^^^^^^
-   |
-   = note: see issue #31844 <https://github.com/rust-lang/rust/issues/31844> for more information
-   = help: consider using `min_specialization` instead, which is more stable and complete
-   = note: `#[warn(incomplete_features)]` on by default
-
-error[E0119]: conflicting implementations of trait `Y` for type `<() as X>::U`
-  --> $DIR/default-item-normalization-ambig-1.rs:20:1
-   |
-LL | impl Y for <() as X>::U {}
-   | ----------------------- first implementation here
-LL | impl Y for <i32 as X>::U {}
-   | ^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `<() as X>::U`
-
-error: aborting due to 1 previous error; 1 warning emitted
-
-For more information about this error, try `rustc --explain E0119`.

tests/ui/specialization/defaultimpl/specialization-no-default.rs

@@ -71,8 +71,7 @@ impl<T: Clone> Redundant for T {
 }
 
 default impl Redundant for i32 {
-    fn redundant(&self) {}
-    //~^ ERROR `redundant` specializes an item from a parent `impl`, but that item is not marked `default`
+    fn redundant(&self) {} //~ ERROR E0520
 }
 
 fn main() {}

tests/ui/specialization/specialization-default-items-drop-coherence.current.stderr

@@ -1,12 +0,0 @@
-error[E0119]: conflicting implementations of trait `Overlap` for type `u32`
-  --> $DIR/specialization-default-items-drop-coherence.rs:26:1
-   |
-LL | impl Overlap for u32 {
-   | -------------------- first implementation here
-...
-LL | impl Overlap for <u32 as Default>::Id {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `u32`
-
-error: aborting due to 1 previous error
-
-For more information about this error, try `rustc --explain E0119`.

tests/ui/specialization/specialization-default-items-drop-coherence.next.stderr

@@ -1,5 +1,5 @@
 error[E0119]: conflicting implementations of trait `Overlap` for type `u32`
-  --> $DIR/specialization-default-items-drop-coherence.rs:26:1
+  --> $DIR/specialization-default-items-drop-coherence.rs:29:1
    |
 LL | impl Overlap for u32 {
    | -------------------- first implementation here

tests/ui/specialization/specialization-default-items-drop-coherence.rs

@@ -1,5 +1,8 @@
-//@ revisions: current next
+//@ revisions: classic coherence next
 //@[next] compile-flags: -Znext-solver
+//@[coherence] compile-flags: -Znext-solver=coherence
+//@[classic] check-pass
+//@[classic] known-bug: #105782
 
 // Should fail. Default items completely drop candidates instead of ambiguity,
 // which is unsound during coherence, since coherence requires completeness.
@@ -24,7 +27,8 @@ impl Overlap for u32 {
 }
 
 impl Overlap for <u32 as Default>::Id {
-    //~^ ERROR conflicting implementations of trait `Overlap` for type `u32`
+    //[coherence]~^ ERROR conflicting implementations of trait `Overlap` for type `u32`
+    //[next]~^^ ERROR conflicting implementations of trait `Overlap` for type `u32`
     type Assoc = Box<usize>;
 }
 

tests/ui/specialization/specialization-overlap-projection.current.stderr

@@ -1,5 +1,5 @@
 warning: the feature `specialization` is incomplete and may not be safe to use and/or cause compiler crashes
-  --> $DIR/specialization-overlap-projection.rs:4:12
+  --> $DIR/specialization-overlap-projection.rs:10:12
    |
 LL | #![feature(specialization)]
    |            ^^^^^^^^^^^^^^
@@ -8,23 +8,5 @@ LL | #![feature(specialization)]
    = help: consider using `min_specialization` instead, which is more stable and complete
    = note: `#[warn(incomplete_features)]` on by default
 
-error[E0119]: conflicting implementations of trait `Foo` for type `u32`
-  --> $DIR/specialization-overlap-projection.rs:19:1
-   |
-LL | impl Foo for u32 {}
-   | ---------------- first implementation here
-LL | impl Foo for <u8 as Assoc>::Output {}
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `u32`
+warning: 1 warning emitted
 
-error[E0119]: conflicting implementations of trait `Foo` for type `u32`
-  --> $DIR/specialization-overlap-projection.rs:21:1
-   |
-LL | impl Foo for u32 {}
-   | ---------------- first implementation here
-...
-LL | impl Foo for <u16 as Assoc>::Output {}
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `u32`
-
-error: aborting due to 2 previous errors; 1 warning emitted
-
-For more information about this error, try `rustc --explain E0119`.

tests/ui/specialization/specialization-overlap-projection.next.stderr

@@ -1,5 +1,5 @@
 warning: the feature `specialization` is incomplete and may not be safe to use and/or cause compiler crashes
-  --> $DIR/specialization-overlap-projection.rs:4:12
+  --> $DIR/specialization-overlap-projection.rs:10:12
    |
 LL | #![feature(specialization)]
    |            ^^^^^^^^^^^^^^
@@ -9,7 +9,7 @@ LL | #![feature(specialization)]
    = note: `#[warn(incomplete_features)]` on by default
 
 error[E0119]: conflicting implementations of trait `Foo` for type `u32`
-  --> $DIR/specialization-overlap-projection.rs:19:1
+  --> $DIR/specialization-overlap-projection.rs:25:1
    |
 LL | impl Foo for u32 {}
    | ---------------- first implementation here
@@ -17,7 +17,7 @@ LL | impl Foo for <u8 as Assoc>::Output {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `u32`
 
 error[E0119]: conflicting implementations of trait `Foo` for type `u32`
-  --> $DIR/specialization-overlap-projection.rs:21:1
+  --> $DIR/specialization-overlap-projection.rs:27:1
    |
 LL | impl Foo for u32 {}
    | ---------------- first implementation here

tests/ui/specialization/specialization-overlap-projection.rs

@@ -1,8 +1,13 @@
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
+//@[current] check-pass
+
 // Test that impls on projected self types can resolve overlap, even when the
 // projections involve specialization, so long as the associated type is
 // provided by the most specialized impl.
-#![feature(specialization)]
-//~^ WARN the feature `specialization` is incomplete and may not be safe to use and/or cause compiler crashes
+
+#![feature(specialization)] //~ WARN the feature `specialization` is incomplete
 
 trait Assoc {
     type Output;
@@ -18,8 +23,8 @@ impl Assoc for u16 { type Output = u16; }
 trait Foo {}
 impl Foo for u32 {}
 impl Foo for <u8 as Assoc>::Output {}
-//~^ ERROR conflicting implementations of trait `Foo` for type `u32`
+//[next]~^ ERROR conflicting implementations of trait `Foo` for type `u32`
 impl Foo for <u16 as Assoc>::Output {}
-//~^ ERROR conflicting implementations of trait `Foo` for type `u32`
+//[next]~^ ERROR conflicting implementations of trait `Foo` for type `u32`
 
 fn main() {}

tests/ui/specialization/specialization-overlap-projection.stderr

@@ -1,30 +0,0 @@
-warning: the feature `specialization` is incomplete and may not be safe to use and/or cause compiler crashes
-  --> $DIR/specialization-overlap-projection.rs:4:12
-   |
-LL | #![feature(specialization)]
-   |            ^^^^^^^^^^^^^^
-   |
-   = note: see issue #31844 <https://github.com/rust-lang/rust/issues/31844> for more information
-   = help: consider using `min_specialization` instead, which is more stable and complete
-   = note: `#[warn(incomplete_features)]` on by default
-
-error[E0119]: conflicting implementations of trait `Foo` for type `u32`
-  --> $DIR/specialization-overlap-projection.rs:20:1
-   |
-LL | impl Foo for u32 {}
-   | ---------------- first implementation here
-LL | impl Foo for <u8 as Assoc>::Output {}
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `u32`
-
-error[E0119]: conflicting implementations of trait `Foo` for type `u32`
-  --> $DIR/specialization-overlap-projection.rs:22:1
-   |
-LL | impl Foo for u32 {}
-   | ---------------- first implementation here
-...
-LL | impl Foo for <u16 as Assoc>::Output {}
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `u32`
-
-error: aborting due to 2 previous errors; 1 warning emitted
-
-For more information about this error, try `rustc --explain E0119`.

tests/ui/traits/alias/issue-83613.rs

@@ -8,5 +8,5 @@ fn mk_opaque() -> OpaqueType {
 trait AnotherTrait {}
 impl<T: Send> AnotherTrait for T {}
 impl AnotherTrait for OpaqueType {}
-//~^ ERROR conflicting implementations of trait `AnotherTrait`
+//~^ ERROR conflicting implementations of trait `AnotherTrait` for type `OpaqueType`
 fn main() {}

tests/ui/traits/alias/issue-83613.stderr

@@ -1,10 +1,10 @@
-error[E0119]: conflicting implementations of trait `AnotherTrait`
+error[E0119]: conflicting implementations of trait `AnotherTrait` for type `OpaqueType`
   --> $DIR/issue-83613.rs:10:1
    |
 LL | impl<T: Send> AnotherTrait for T {}
    | -------------------------------- first implementation here
 LL | impl AnotherTrait for OpaqueType {}
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `OpaqueType`
 
 error: aborting due to 1 previous error
 

tests/ui/traits/issue-105231.rs

@@ -1,3 +1,4 @@
+//~ ERROR overflow evaluating the requirement `A<A<A<A<A<A<A<...>>>>>>>: Send`
 struct A<T>(B<T>);
 //~^ ERROR recursive types `A` and `B` have infinite size
 //~| ERROR `T` is only used recursively
@@ -6,5 +7,5 @@ struct B<T>(A<A<T>>);
 trait Foo {}
 impl<T> Foo for T where T: Send {}
 impl Foo for B<u8> {}
-//~^ ERROR conflicting implementations of trait `Foo` for type `B<u8>`
+
 fn main() {}

tests/ui/traits/issue-105231.stderr

@@ -1,5 +1,5 @@
 error[E0072]: recursive types `A` and `B` have infinite size
-  --> $DIR/issue-105231.rs:1:1
+  --> $DIR/issue-105231.rs:2:1
    |
 LL | struct A<T>(B<T>);
    | ^^^^^^^^^^^ ---- recursive without indirection
@@ -16,7 +16,7 @@ LL ~ struct B<T>(Box<A<A<T>>>);
    |
 
 error: type parameter `T` is only used recursively
-  --> $DIR/issue-105231.rs:1:15
+  --> $DIR/issue-105231.rs:2:15
    |
 LL | struct A<T>(B<T>);
    |          -    ^
@@ -27,7 +27,7 @@ LL | struct A<T>(B<T>);
    = note: all type parameters must be used in a non-recursive way in order to constrain their variance
 
 error: type parameter `T` is only used recursively
-  --> $DIR/issue-105231.rs:4:17
+  --> $DIR/issue-105231.rs:5:17
    |
 LL | struct B<T>(A<A<T>>);
    |          -      ^
@@ -37,18 +37,16 @@ LL | struct B<T>(A<A<T>>);
    = help: consider removing `T`, referring to it in a field, or using a marker such as `PhantomData`
    = note: all type parameters must be used in a non-recursive way in order to constrain their variance
 
-error[E0119]: conflicting implementations of trait `Foo` for type `B<u8>`
-  --> $DIR/issue-105231.rs:8:1
+error[E0275]: overflow evaluating the requirement `A<A<A<A<A<A<A<...>>>>>>>: Send`
    |
-LL | impl<T> Foo for T where T: Send {}
-   | ------------------------------- first implementation here
-LL | impl Foo for B<u8> {}
-   | ^^^^^^^^^^^^^^^^^^ conflicting implementation for `B<u8>`
-   |
-   = note: overflow evaluating the requirement `B<u8>: Send`
    = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`issue_105231`)
+note: required because it appears within the type `B<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<u8>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>`
+  --> $DIR/issue-105231.rs:5:8
+   |
+LL | struct B<T>(A<A<T>>);
+   |        ^
 
 error: aborting due to 4 previous errors
 
-Some errors have detailed explanations: E0072, E0119.
+Some errors have detailed explanations: E0072, E0275.
 For more information about an error, try `rustc --explain E0072`.

tests/ui/traits/solver-cycles/cycle-via-builtin-auto-trait-impl.rs

@@ -1,3 +1,4 @@
+//~ ERROR overflow
 // A regression test for #111729 checking that we correctly
 // track recursion depth for obligations returned by confirmation.
 use std::panic::RefUnwindSafe;
@@ -17,7 +18,6 @@ impl<T: RefUnwindSafe> Database for T {
     type Storage = SalsaStorage;
 }
 impl Database for RootDatabase {
-    //~^ ERROR conflicting implementations of trait `Database` for type `RootDatabase`
     type Storage = SalsaStorage;
 }
 

tests/ui/traits/solver-cycles/cycle-via-builtin-auto-trait-impl.stderr

@@ -1,12 +1,24 @@
-error[E0119]: conflicting implementations of trait `Database` for type `RootDatabase`
-  --> $DIR/cycle-via-builtin-auto-trait-impl.rs:19:1
+error[E0275]: overflow evaluating the requirement `Runtime<RootDatabase>: RefUnwindSafe`
+   |
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`cycle_via_builtin_auto_trait_impl`)
+note: required because it appears within the type `RootDatabase`
+  --> $DIR/cycle-via-builtin-auto-trait-impl.rs:13:8
+   |
+LL | struct RootDatabase {
+   |        ^^^^^^^^^^^^
+note: required for `RootDatabase` to implement `Database`
+  --> $DIR/cycle-via-builtin-auto-trait-impl.rs:17:24
    |
 LL | impl<T: RefUnwindSafe> Database for T {
-   | ------------------------------------- first implementation here
-...
-LL | impl Database for RootDatabase {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `RootDatabase`
+   |         -------------  ^^^^^^^^     ^
+   |         |
+   |         unsatisfied trait bound introduced here
+note: required because it appears within the type `Runtime<RootDatabase>`
+  --> $DIR/cycle-via-builtin-auto-trait-impl.rs:24:8
+   |
+LL | struct Runtime<DB: Database> {
+   |        ^^^^^^^
 
 error: aborting due to 1 previous error
 
-For more information about this error, try `rustc --explain E0119`.
+For more information about this error, try `rustc --explain E0275`.