2 files changed, 63 insertions, 0 deletions

diff --git a/tests/ui/issues/issue-37291/auxiliary/lib.rs b/tests/ui/issues/issue-37291/auxiliary/lib.rs
new file mode 100644
index 000000000..1b163ee13
--- /dev/null
+++ b/tests/ui/issues/issue-37291/auxiliary/lib.rs
@@ -0,0 +1,42 @@
+#![crate_type = "lib"]
+
+use std::ops::Mul;
+
+pub trait A {}
+pub trait B {
+    type AT: A;
+}
+pub trait C {
+    type BT: B;
+}
+
+pub struct AV;
+impl A for AV {}
+
+pub struct BV;
+impl B for BV {
+    type AT = AV;
+}
+
+pub struct CV;
+impl C for CV {
+    type BT = BV;
+}
+
+pub struct WrapperB<T>(pub T);
+pub struct WrapperC<T>(pub T);
+
+impl<C1> Mul<WrapperB<<C1::BT as B>::AT>> for WrapperC<C1>
+    where C1: C
+{
+    type Output = u8;
+    fn mul(self, _: WrapperB<<C1::BT as B>::AT>) -> Self::Output {
+        loop {}
+    }
+}
+impl<C1> Mul<WrapperC<C1>> for WrapperC<C1> {
+    type Output = u8;
+    fn mul(self, _: WrapperC<C1>) -> Self::Output {
+        loop {}
+    }
+}
diff --git a/tests/ui/issues/issue-37291/main.rs b/tests/ui/issues/issue-37291/main.rs
new file mode 100644
index 000000000..6fb6b50da
--- /dev/null
+++ b/tests/ui/issues/issue-37291/main.rs
@@ -0,0 +1,21 @@
+// run-pass
+#![allow(unused_imports)]
+// aux-build:lib.rs
+
+// Regression test for #37291. The problem was that the starting
+// environment for a specialization check was not including the
+// where-clauses from the impl when attempting to normalize the impl's
+// trait-ref, so things like `<C as Foo>::Item` could not resolve,
+// since the `C: Foo` trait bound was not included in the environment.
+
+extern crate lib;
+
+use lib::{CV, WrapperB, WrapperC};
+
+fn main() {
+    let a = WrapperC(CV);
+    let b = WrapperC(CV);
+    if false {
+        let _ = a * b;
+    }
+}