add tests

tests/ui/dyn-star/param-env-region-infer.current.stderr

@@ -1,5 +1,5 @@
 error[E0282]: type annotations needed
-  --> $DIR/param-env-region-infer.rs:18:10
+  --> $DIR/param-env-region-infer.rs:19:10
    |
 LL |     t as _
    |          ^ cannot infer type

tests/ui/dyn-star/param-env-region-infer.next.stderr

@@ -1,30 +0,0 @@
-error[E0391]: cycle detected when computing type of `make_dyn_star::{opaque#0}`
-  --> $DIR/param-env-region-infer.rs:16:60
-   |
-LL | fn make_dyn_star<'a, T: PointerLike + Debug + 'a>(t: T) -> impl PointerLike + Debug + 'a {
-   |                                                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-note: ...which requires type-checking `make_dyn_star`...
-  --> $DIR/param-env-region-infer.rs:16:1
-   |
-LL | fn make_dyn_star<'a, T: PointerLike + Debug + 'a>(t: T) -> impl PointerLike + Debug + 'a {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   = note: ...which requires computing layout of `make_dyn_star::{opaque#0}`...
-   = note: ...which requires normalizing `make_dyn_star::{opaque#0}`...
-   = note: ...which again requires computing type of `make_dyn_star::{opaque#0}`, completing the cycle
-note: cycle used when checking item types in top-level module
-  --> $DIR/param-env-region-infer.rs:10:1
-   |
-LL | / #![feature(dyn_star, pointer_like_trait)]
-LL | | #![allow(incomplete_features)]
-LL | |
-LL | | use std::fmt::Debug;
-...  |
-LL | |
-LL | | fn main() {}
-   | |____________^
-   = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information
-
-error: aborting due to previous error
-
-For more information about this error, try `rustc --explain E0391`.

tests/ui/dyn-star/param-env-region-infer.rs

@@ -1,9 +1,10 @@
-// revisions: current next
-// Need `-Zdeduplicate-diagnostics=yes` because the number of cycle errors
-// emitted is for some horrible reason platform-specific.
-//[next] compile-flags: -Ztrait-solver=next -Zdeduplicate-diagnostics=yes
+// revisions: current
 // incremental
 
+// FIXME(-Ztrait-solver=next): 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.
+
 // checks that we don't ICE if there are region inference variables in the environment
 // when computing `PointerLike` builtin candidates.
 

tests/ui/traits/new-solver/coinduction/fixpoint-exponential-growth.rs

@@ -0,0 +1,32 @@
+// compile-flags: -Ztrait-solver=next
+
+// Proving `W<?0>: Trait` instantiates `?0` with `(W<?1>, W<?2>)` and then
+// proves `W<?1>: Trait` and `W<?2>: Trait`, resulting in a coinductive cycle.
+//
+// Proving coinductive cycles runs until we reach a fixpoint. This fixpoint is
+// never reached here and each step doubles the amount of nested obligations.
+//
+// This previously caused a hang in the trait solver, see
+// https://github.com/rust-lang/trait-system-refactor-initiative/issues/13.
+
+#![feature(rustc_attrs)]
+
+#[rustc_coinductive]
+trait Trait {}
+
+struct W<T>(T);
+
+impl<T, U> Trait for W<(W<T>, W<U>)>
+where
+    W<T>: Trait,
+    W<U>: Trait,
+{
+}
+
+fn impls<T: Trait>() {}
+
+fn main() {
+    impls::<W<_>>();
+    //~^ ERROR type annotations needed
+    //~| ERROR overflow evaluating the requirement
+}

tests/ui/traits/new-solver/coinduction/fixpoint-exponential-growth.stderr

@@ -0,0 +1,23 @@
+error[E0282]: type annotations needed
+  --> $DIR/fixpoint-exponential-growth.rs:29:5
+   |
+LL |     impls::<W<_>>();
+   |     ^^^^^^^^^^^^^ cannot infer type of the type parameter `T` declared on the function `impls`
+
+error[E0275]: overflow evaluating the requirement `W<_>: Trait`
+  --> $DIR/fixpoint-exponential-growth.rs:29:5
+   |
+LL |     impls::<W<_>>();
+   |     ^^^^^^^^^^^^^
+   |
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`fixpoint_exponential_growth`)
+note: required by a bound in `impls`
+  --> $DIR/fixpoint-exponential-growth.rs:26:13
+   |
+LL | fn impls<T: Trait>() {}
+   |             ^^^^^ required by this bound in `impls`
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0275, E0282.
+For more information about an error, try `rustc --explain E0275`.

tests/ui/traits/new-solver/coinduction/incompleteness-unstable-result.rs

@@ -0,0 +1,69 @@
+// compile-flags: -Ztrait-solver=next
+#![feature(rustc_attrs)]
+
+// This test is incredibly subtle. At its core the goal is to get a coinductive cycle,
+// which, depending on its root goal, either holds or errors. We achieve this by getting
+// incomplete inference via a `ParamEnv` candidate in the `A<T>` impl and required
+// inference from an `Impl` candidate in the `B<T>` impl.
+//
+// To make global cache accesses stronger than the guidance from the where-bounds, we add
+// another coinductive cycle from `A<T>: Trait<U, V, D>` to `A<T>: Trait<U, D, V>` and only
+// constrain `D` directly. This means that any candidates which rely on `V` only make
+// progress in the second iteration, allowing a cache access in the first iteration to take
+// precedence.
+//
+// tl;dr: our caching of coinductive cycles was broken and this is a regression
+// test for that.
+
+#[rustc_coinductive]
+trait Trait<T: ?Sized, V: ?Sized, D: ?Sized> {}
+struct A<T: ?Sized>(*const T);
+struct B<T: ?Sized>(*const T);
+
+trait IncompleteGuidance<T: ?Sized, V: ?Sized> {}
+impl<T: ?Sized, U: ?Sized + 'static> IncompleteGuidance<U, u8> for T {}
+impl<T: ?Sized, U: ?Sized + 'static> IncompleteGuidance<U, i8> for T {}
+impl<T: ?Sized, U: ?Sized + 'static> IncompleteGuidance<U, i16> for T {}
+
+trait ImplGuidance<T: ?Sized, V: ?Sized> {}
+impl<T: ?Sized> ImplGuidance<u32, u8> for T {}
+impl<T: ?Sized> ImplGuidance<i32, i8> for T {}
+
+impl<T: ?Sized, U: ?Sized, V: ?Sized, D: ?Sized> Trait<U, V, D> for A<T>
+where
+    T: IncompleteGuidance<U, V>,
+    A<T>: Trait<U, D, V>,
+    B<T>: Trait<U, V, D>,
+    (): ToU8<D>,
+{
+}
+
+trait ToU8<T: ?Sized> {}
+impl ToU8<u8> for () {}
+
+impl<T: ?Sized, U: ?Sized, V: ?Sized, D: ?Sized> Trait<U, V, D> for B<T>
+where
+    T: ImplGuidance<U, V>,
+    A<T>: Trait<U, V, D>,
+{
+}
+
+fn impls_trait<T: ?Sized + Trait<U, V, D>, U: ?Sized, V: ?Sized, D: ?Sized>() {}
+
+fn with_bound<X>()
+where
+    X: IncompleteGuidance<i32, u8>,
+    X: IncompleteGuidance<u32, i8>,
+    X: IncompleteGuidance<u32, i16>,
+{
+    impls_trait::<B<X>, _, _, _>(); // entering the cycle from `B` works
+
+    // entering the cycle from `A` fails, but would work if we were to use the cache
+    // result of `B<X>`.
+    impls_trait::<A<X>, _, _, _>();
+    //~^ ERROR the trait bound `A<X>: Trait<_, _, _>` is not satisfied
+}
+
+fn main() {
+    with_bound::<u32>();
+}

tests/ui/traits/new-solver/coinduction/incompleteness-unstable-result.stderr

@@ -0,0 +1,16 @@
+error[E0277]: the trait bound `A<X>: Trait<_, _, _>` is not satisfied
+  --> $DIR/incompleteness-unstable-result.rs:63:19
+   |
+LL |     impls_trait::<A<X>, _, _, _>();
+   |                   ^^^^ the trait `Trait<_, _, _>` is not implemented for `A<X>`
+   |
+   = help: the trait `Trait<U, V, D>` is implemented for `A<T>`
+note: required by a bound in `impls_trait`
+  --> $DIR/incompleteness-unstable-result.rs:51:28
+   |
+LL | fn impls_trait<T: ?Sized + Trait<U, V, D>, U: ?Sized, V: ?Sized, D: ?Sized>() {}
+   |                            ^^^^^^^^^^^^^^ required by this bound in `impls_trait`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/traits/new-solver/overflow/global-cache.rs

@@ -0,0 +1,23 @@
+// compile-flags: -Ztrait-solver=next
+
+// Check that we consider the reached depth of global cache
+// entries when detecting overflow. We would otherwise be unstable
+// wrt to incremental compilation.
+#![recursion_limit = "9"]
+
+trait Trait {}
+
+struct Inc<T>(T);
+
+impl<T: Trait> Trait for Inc<T> {}
+impl Trait for () {}
+
+fn impls_trait<T: Trait>() {}
+
+type Four<T> = Inc<Inc<Inc<Inc<T>>>>;
+
+fn main() {
+    impls_trait::<Four<Four<()>>>();
+    impls_trait::<Four<Four<Four<Four<()>>>>>();
+    //~^ ERROR overflow evaluating the requirement
+}

tests/ui/traits/new-solver/overflow/global-cache.stderr

@@ -0,0 +1,16 @@
+error[E0275]: overflow evaluating the requirement `Inc<Inc<Inc<Inc<Inc<Inc<Inc<...>>>>>>>: Trait`
+  --> $DIR/global-cache.rs:21:5
+   |
+LL |     impls_trait::<Four<Four<Four<Four<()>>>>>();
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "18"]` attribute to your crate (`global_cache`)
+note: required by a bound in `impls_trait`
+  --> $DIR/global-cache.rs:15:19
+   |
+LL | fn impls_trait<T: Trait>() {}
+   |                   ^^^^^ required by this bound in `impls_trait`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0275`.