1 files changed, 50 insertions, 0 deletions
diff --git a/src/test/ui/specialization/issue-39448.rs b/src/test/ui/specialization/issue-39448.rs
new file mode 100644
index 000000000..a15c4bd6b
--- /dev/null
+++ b/src/test/ui/specialization/issue-39448.rs
@@ -0,0 +1,50 @@
+#![feature(specialization)] //~ WARN the feature `specialization` is incomplete
+
+// Regression test for a specialization-related ICE (#39448).
+
+trait A: Sized {
+    fn foo(self, _: Self) -> Self {
+        self
+    }
+}
+
+impl A for u8 {}
+impl A for u16 {}
+
+impl FromA<u8> for u16 {
+    fn from(x: u8) -> u16 {
+        x as u16
+    }
+}
+
+trait FromA<T> {
+    fn from(t: T) -> Self;
+}
+
+impl<T: A, U: A + FromA<T>> FromA<T> for U {
+    default fn from(x: T) -> Self {
+        ToA::to(x)
+    }
+}
+
+trait ToA<T> {
+    fn to(self) -> T;
+}
+
+impl<T, U> ToA<U> for T
+where
+    U: FromA<T>,
+{
+    fn to(self) -> U {
+        U::from(self)
+    }
+}
+
+#[allow(dead_code)]
+fn foo<T: A, U: A>(x: T, y: U) -> U {
+    x.foo(y.to()).to() //~ ERROR overflow evaluating the requirement
+}
+
+fn main() {
+    let z = foo(8u8, 1u16);
+}