2 files changed, 57 insertions, 0 deletions
diff --git a/tests/ui/autoref-autoderef/deref-ambiguity-becomes-nonambiguous.rs b/tests/ui/autoref-autoderef/deref-ambiguity-becomes-nonambiguous.rs
new file mode 100644
index 000000000..d8034d57e
--- /dev/null
+++ b/tests/ui/autoref-autoderef/deref-ambiguity-becomes-nonambiguous.rs
@@ -0,0 +1,40 @@
+use std::ops::Deref;
+use std::rc::Rc;
+
+struct Value<T>(T);
+
+pub trait Wrap<T> {
+    fn wrap() -> Self;
+}
+
+impl<R, A1, A2> Wrap<fn(A1, A2) -> R> for Value<fn(A1, A2) -> R> {
+    fn wrap() -> Self {
+        todo!()
+    }
+}
+
+impl<F, R, A1, A2> Wrap<F> for Value<Rc<dyn Fn(A1, A2) -> R>> {
+    fn wrap() -> Self {
+        todo!()
+    }
+}
+
+impl<F> Deref for Value<Rc<F>> {
+    type Target = F;
+
+    fn deref(&self) -> &Self::Target {
+        &*self.0
+    }
+}
+
+fn main() {
+    let var_fn = Value::wrap();
+    //~^ ERROR type annotations needed for `Value<Rc<_>>`
+
+    // The combination of `Value: Wrap` obligation plus the autoderef steps
+    // (caused by the `Deref` impl above) actually means that the self type
+    // of the method fn below is constrained to be `Value<Rc<dyn Fn(?0, ?1) -> ?2>>`.
+    // However, that's only known to us on the error path -- we still need
+    // to emit an ambiguity error, though.
+    let _ = var_fn.clone();
+}
diff --git a/tests/ui/autoref-autoderef/deref-ambiguity-becomes-nonambiguous.stderr b/tests/ui/autoref-autoderef/deref-ambiguity-becomes-nonambiguous.stderr
new file mode 100644
index 000000000..06a7e9085
--- /dev/null
+++ b/tests/ui/autoref-autoderef/deref-ambiguity-becomes-nonambiguous.stderr
@@ -0,0 +1,17 @@
+error[E0282]: type annotations needed for `Value<Rc<_>>`
+  --> $DIR/deref-ambiguity-becomes-nonambiguous.rs:31:9
+   |
+LL |     let var_fn = Value::wrap();
+   |         ^^^^^^
+...
+LL |     let _ = var_fn.clone();
+   |                    ----- type must be known at this point
+   |
+help: consider giving `var_fn` an explicit type, where the placeholders `_` are specified
+   |
+LL |     let var_fn: Value<Rc<_>> = Value::wrap();
+   |               ++++++++++++++
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0282`.