implement the skeleton of the updated trait solver

2 files changed, 54 insertions, 0 deletions

diff --git a/src/test/ui/traits/solver-cycles/inductive-canonical-cycle.rs b/src/test/ui/traits/solver-cycles/inductive-canonical-cycle.rs
new file mode 100644
index 00000000000..a3bb76d7e3b
--- /dev/null
+++ b/src/test/ui/traits/solver-cycles/inductive-canonical-cycle.rs
@@ -0,0 +1,28 @@
+// known-bug
+
+// This should compile but fails with the current solver.
+//
+// This checks that the new solver uses `Ambiguous` when hitting the
+// inductive cycle here when proving `exists<^0, ^1> (): Trait<^0, ^1>`
+// which requires proving `Trait<?1, ?0>` but that has the same
+// canonical representation.
+trait Trait<T, U> {}
+
+impl<T, U> Trait<T, U> for ()
+where
+    (): Trait<U, T>,
+    T: OtherTrait,
+{}
+
+trait OtherTrait {}
+impl OtherTrait for u32 {}
+
+fn require_trait<T, U>()
+where
+    (): Trait<T, U>
+{}
+
+fn main() {
+    require_trait::<_, _>();
+    //~^ ERROR overflow evaluating
+}
diff --git a/src/test/ui/traits/solver-cycles/inductive-canonical-cycle.stderr b/src/test/ui/traits/solver-cycles/inductive-canonical-cycle.stderr
new file mode 100644
index 00000000000..e4b84e07822
--- /dev/null
+++ b/src/test/ui/traits/solver-cycles/inductive-canonical-cycle.stderr
@@ -0,0 +1,26 @@
+error[E0275]: overflow evaluating the requirement `_: Sized`
+  --> $DIR/inductive-canonical-cycle.rs:26:5
+   |
+LL |     require_trait::<_, _>();
+   |     ^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`inductive_canonical_cycle`)
+note: required for `()` to implement `Trait<_, _>`
+  --> $DIR/inductive-canonical-cycle.rs:11:12
+   |
+LL | impl<T, U> Trait<T, U> for ()
+   |            ^^^^^^^^^^^     ^^
+   = note: 128 redundant requirements hidden
+   = note: required for `()` to implement `Trait<_, _>`
+note: required by a bound in `require_trait`
+  --> $DIR/inductive-canonical-cycle.rs:22:9
+   |
+LL | fn require_trait<T, U>()
+   |    ------------- required by a bound in this
+LL | where
+LL |     (): Trait<T, U>
+   |         ^^^^^^^^^^^ required by this bound in `require_trait`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0275`.