1 files changed, 53 insertions, 0 deletions
diff --git a/tests/ui/traits/next-solver/cycles/fixpoint-rerun-all-cycle-heads.rs b/tests/ui/traits/next-solver/cycles/fixpoint-rerun-all-cycle-heads.rs
new file mode 100644
index 000000000..c7e2e2d5e
--- /dev/null
+++ b/tests/ui/traits/next-solver/cycles/fixpoint-rerun-all-cycle-heads.rs
@@ -0,0 +1,53 @@
+// compile-flags: -Znext-solver
+#![feature(rustc_attrs)]
+
+// Check that we correctly rerun the trait solver for heads of cycles,
+// even if they are not the root.
+
+struct A<T: ?Sized>(*const T);
+struct B<T: ?Sized>(*const T);
+struct C<T: ?Sized>(*const T);
+
+#[rustc_coinductive]
+trait Trait<'a, 'b> {}
+trait NotImplemented {}
+
+impl<'a, 'b, T: ?Sized> Trait<'a, 'b> for A<T> where B<T>: Trait<'a, 'b> {}
+
+// With this the root of `B<T>` is `A<T>`, even if the other impl does
+// not have a cycle with `A<T>`. This candidate never applies because of
+// the `A<T>: NotImplemented` bound.
+impl<'a, 'b, T: ?Sized> Trait<'a, 'b> for B<T>
+where
+    A<T>: Trait<'a, 'b>,
+    A<T>: NotImplemented,
+{
+}
+
+// This impl directly requires 'b to be equal to 'static.
+//
+// Because of the coinductive cycle through `C<T>` it also requires
+// 'a to be 'static.
+impl<'a, T: ?Sized> Trait<'a, 'static> for B<T>
+where
+    C<T>: Trait<'a, 'a>,
+{}
+
+// In the first iteration of `B<T>: Trait<'a, 'b>` we don't add any
+// constraints here, only after setting the provisional result to require
+// `'b == 'static` do we also add that constraint for `'a`.
+impl<'a, 'b, T: ?Sized> Trait<'a, 'b> for C<T>
+where
+    B<T>: Trait<'a, 'b>,
+{}
+
+fn impls_trait<'a, 'b, T: Trait<'a, 'b> + ?Sized>() {}
+
+fn check<'a, T: ?Sized>() {
+    impls_trait::<'a, 'static, A<T>>();
+    //~^ ERROR lifetime may not live long enough
+}
+
+fn main() {
+    check::<()>();
+}