Rollup merge of #48610 - ishitatsuyuki:ishitatsuyuki-patch-1, r=nikomatsakis

Add regression test for #48551

[Issue link](https://github.com/rust-lang/rust/issues/48551)

src/test/run-pass/issue-48551.rs

@@ -0,0 +1,43 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Regression test for #48551. Covers a case where duplicate candidates
+// arose during associated type projection.
+
+use std::ops::{Mul, MulAssign};
+
+pub trait ClosedMul<Right>: Sized + Mul<Right, Output = Self> + MulAssign<Right> {}
+impl<T, Right> ClosedMul<Right> for T
+where
+    T: Mul<Right, Output = T> + MulAssign<Right>,
+{
+}
+
+pub trait InnerSpace: ClosedMul<<Self as InnerSpace>::Real> {
+    type Real;
+}
+
+pub trait FiniteDimVectorSpace: ClosedMul<<Self as FiniteDimVectorSpace>::Field> {
+    type Field;
+}
+
+pub trait FiniteDimInnerSpace
+    : InnerSpace + FiniteDimVectorSpace<Field = <Self as InnerSpace>::Real> {
+}
+
+pub trait EuclideanSpace: ClosedMul<<Self as EuclideanSpace>::Real> {
+    type Coordinates: FiniteDimInnerSpace<Real = Self::Real>
+        + Mul<Self::Real, Output = Self::Coordinates>
+        + MulAssign<Self::Real>;
+
+    type Real;
+}
+
+fn main() {}