oops! new unsoundness

Bless tests and show an introduced unsoundness related to
exits<'a> { forall<'b> { 'a == 'b } }.
We now resolve the var ?a in U0 to the placeholder !b in U1.

Author: aliemjay

tests/ui/higher-rank-trait-bounds/hrtb-exists-forall-trait-invariant.rs

@@ -2,6 +2,9 @@
 //
 // In particular, we test this pattern in trait solving, where it is not connected
 // to any part of the source code.
+//
+// check-pass
+// Oops!
 
 use std::cell::Cell;
 
@@ -25,5 +28,5 @@ fn main() {
     //     yielding `fn(&!b u32)`, in a fresh universe U1
     //   - So we get `?a = !b` but the universe U0 assigned to `?a` cannot name `!b`.
 
-    foo::<()>(); //~ ERROR implementation of `Trait` is not general enough
+    foo::<()>();
 }

tests/ui/higher-rank-trait-bounds/hrtb-exists-forall-trait-invariant.stderr

@@ -14,12 +14,6 @@ LL | fn give_some<'a>() {
    |              -- lifetime `'a` defined here
 LL |     want_hrtb::<&'a u32>()
    |     ^^^^^^^^^^^^^^^^^^^^ requires that `'a` must outlive `'static`
-   |
-note: due to current limitations in the borrow checker, this implies a `'static` lifetime
-  --> $DIR/hrtb-just-for-static.rs:9:15
-   |
-LL |     where T : for<'a> Foo<&'a isize>
-   |               ^^^^^^^^^^^^^^^^^^^^^^
 
 error: implementation of `Foo` is not general enough
   --> $DIR/hrtb-just-for-static.rs:30:5

tests/ui/higher-rank-trait-bounds/hrtb-just-for-static.stderr

@@ -15,9 +15,9 @@ impl<'a> Y for C<'a> {
 struct C<'a>(&'a ());
 struct X<T: Y>(T::P);
 
-impl<T: NotAuto> NotAuto for Box<T> {} //~ NOTE: required
+impl<T: NotAuto> NotAuto for Box<T> {}
+impl<T: Y> NotAuto for X<T> where T::P: NotAuto {} //~ NOTE: required
 //~^ NOTE unsatisfied trait bound introduced here
-impl<T: Y> NotAuto for X<T> where T::P: NotAuto {}
 impl<'a> NotAuto for C<'a> {}
 
 fn is_send<S: NotAuto>() {}
@@ -28,6 +28,4 @@ fn main() {
     // Should only be a few notes.
     is_send::<X<C<'static>>>();
     //~^ ERROR overflow evaluating
-    //~| 3 redundant requirements hidden
-    //~| required for
 }

tests/ui/traits/inductive-overflow/lifetime.rs

@@ -1,18 +1,14 @@
-error[E0275]: overflow evaluating the requirement `X<C<'_>>: NotAuto`
+error[E0275]: overflow evaluating the requirement `Box<X<C<'static>>>: NotAuto`
   --> $DIR/lifetime.rs:29:5
    |
 LL |     is_send::<X<C<'static>>>();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^
    |
-note: required for `Box<X<C<'_>>>` to implement `NotAuto`
-  --> $DIR/lifetime.rs:18:18
+note: required for `X<C<'static>>` to implement `NotAuto`
+  --> $DIR/lifetime.rs:19:12
    |
-LL | impl<T: NotAuto> NotAuto for Box<T> {}
-   |         -------  ^^^^^^^     ^^^^^^
-   |         |
-   |         unsatisfied trait bound introduced here
-   = note: 3 redundant requirements hidden
-   = note: required for `X<C<'static>>` to implement `NotAuto`
+LL | impl<T: Y> NotAuto for X<T> where T::P: NotAuto {}
+   |            ^^^^^^^     ^^^^             ------- unsatisfied trait bound introduced here
 note: required by a bound in `is_send`
   --> $DIR/lifetime.rs:23:15
    |

tests/ui/traits/inductive-overflow/lifetime.stderr

@@ -4,10 +4,10 @@
 pub struct Table<T, const N: usize>([Option<T>; N]);
 
 impl<'a, T, const N: usize> IntoIterator for &'a Table<T, N> {
-    type IntoIter = std::iter::Flatten<std::slice::Iter<'a, T>>; //~ ERROR `&T` is not an iterator
+    type IntoIter = std::iter::Flatten<std::slice::Iter<'a, T>>; //~ ERROR `&'a T` is not an iterator
     type Item = &'a T;
 
-    fn into_iter(self) -> Self::IntoIter { //~ ERROR `&T` is not an iterator
+    fn into_iter(self) -> Self::IntoIter { //~ ERROR `&'a T` is not an iterator
         unimplemented!()
     }
 }

tests/ui/wf/hir-wf-check-erase-regions.rs

@@ -1,24 +1,24 @@
-error[E0277]: `&T` is not an iterator
+error[E0277]: `&'a T` is not an iterator
   --> $DIR/hir-wf-check-erase-regions.rs:7:21
    |
 LL |     type IntoIter = std::iter::Flatten<std::slice::Iter<'a, T>>;
-   |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `&T` is not an iterator
+   |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `&'a T` is not an iterator
    |
-   = help: the trait `Iterator` is not implemented for `&T`
+   = help: the trait `Iterator` is not implemented for `&'a T`
    = help: the trait `Iterator` is implemented for `&mut I`
-   = note: required for `&T` to implement `IntoIterator`
+   = note: required for `&'a T` to implement `IntoIterator`
 note: required by a bound in `Flatten`
   --> $SRC_DIR/core/src/iter/adapters/flatten.rs:LL:COL
 
-error[E0277]: `&T` is not an iterator
+error[E0277]: `&'a T` is not an iterator
   --> $DIR/hir-wf-check-erase-regions.rs:10:27
    |
 LL |     fn into_iter(self) -> Self::IntoIter {
-   |                           ^^^^^^^^^^^^^^ `&T` is not an iterator
+   |                           ^^^^^^^^^^^^^^ `&'a T` is not an iterator
    |
-   = help: the trait `Iterator` is not implemented for `&T`
+   = help: the trait `Iterator` is not implemented for `&'a T`
    = help: the trait `Iterator` is implemented for `&mut I`
-   = note: required for `&T` to implement `IntoIterator`
+   = note: required for `&'a T` to implement `IntoIterator`
 note: required by a bound in `Flatten`
   --> $SRC_DIR/core/src/iter/adapters/flatten.rs:LL:COL