1 files changed, 40 insertions, 0 deletions
diff --git a/tests/ui/traits/new-solver/negative-coherence-bounds.rs b/tests/ui/traits/new-solver/negative-coherence-bounds.rs
new file mode 100644
index 000000000..5436b02c3
--- /dev/null
+++ b/tests/ui/traits/new-solver/negative-coherence-bounds.rs
@@ -0,0 +1,40 @@
+// check-pass
+
+// This test verifies that negative trait predicate cannot be satisfied from a
+// positive param-env candidate.
+
+// Negative coherence is one of the only places where we actually construct and
+// evaluate negative predicates. Specifically, when verifying whether the first
+// and second impls below overlap, we do not want to consider them disjoint,
+// otherwise the second impl would be missing an associated type `type Item`
+// which is provided by the first impl that it is specializing.
+
+#![feature(specialization)]
+//~^ WARN the feature `specialization` is incomplete
+#![feature(with_negative_coherence)]
+
+trait BoxIter {
+    type Item;
+
+    fn last(self) -> Option<Self::Item>;
+}
+
+impl<I: Iterator + ?Sized> BoxIter for Box<I> {
+    type Item = I::Item;
+
+    default fn last(self) -> Option<I::Item> {
+        todo!()
+    }
+}
+
+// When checking that this impl does/doesn't overlap the one above, we evaluate
+// a negative version of all of the where-clause predicates of the impl below.
+// For `I: !Iterator`, we should make sure that the param-env clause `I: Iterator`
+// from above doesn't satisfy this predicate.
+impl<I: Iterator> BoxIter for Box<I> {
+    fn last(self) -> Option<I::Item> {
+        (*self).last()
+    }
+}
+
+fn main() {}