From 5e7fed1f35c1318092fc6bf6d25814026224af8a Mon Sep 17 00:00:00 2001
From: Yuki Okushi <yuki.okushi@huawei.com>
Date: Thu, 1 Jul 2021 08:00:21 +0900
Subject: [PATCH] Add a regression test for issue-63355

---
 .../ui/type-alias-impl-trait/issue-63355.rs   | 50 +++++++++++++++++++
 .../type-alias-impl-trait/issue-63355.stderr  | 14 ++++++
 2 files changed, 64 insertions(+)
 create mode 100644 src/test/ui/type-alias-impl-trait/issue-63355.rs
 create mode 100644 src/test/ui/type-alias-impl-trait/issue-63355.stderr

diff --git a/src/test/ui/type-alias-impl-trait/issue-63355.rs b/src/test/ui/type-alias-impl-trait/issue-63355.rs
new file mode 100644
index 0000000000000..8762d189c7389
--- /dev/null
+++ b/src/test/ui/type-alias-impl-trait/issue-63355.rs
@@ -0,0 +1,50 @@
+#![feature(min_type_alias_impl_trait)]
+#![feature(type_alias_impl_trait)]
+#![allow(incomplete_features)]
+
+pub trait Foo {}
+
+pub trait Bar {
+    type Foo: Foo;
+
+    fn foo() -> Self::Foo;
+}
+
+pub trait Baz {
+    type Foo: Foo;
+    type Bar: Bar<Foo = Self::Foo>;
+
+    fn foo() -> Self::Foo;
+    fn bar() -> Self::Bar;
+}
+
+impl Foo for () {}
+
+impl Bar for () {
+    type Foo = FooImpl;
+
+    fn foo() -> Self::Foo {
+        ()
+    }
+}
+
+// FIXME(#86731): The below is illegal use of `min_type_alias_impl_trait`
+// but the compiler doesn't report it, we should fix it.
+pub type FooImpl = impl Foo;
+pub type BarImpl = impl Bar<Foo = FooImpl>;
+//~^ ERROR: type mismatch resolving `<() as Bar>::Foo == ()`
+
+impl Baz for () {
+    type Foo = FooImpl;
+    type Bar = BarImpl;
+
+    fn foo() -> Self::Foo {
+        ()
+    }
+
+    fn bar() -> Self::Bar {
+        ()
+    }
+}
+
+fn main() {}
diff --git a/src/test/ui/type-alias-impl-trait/issue-63355.stderr b/src/test/ui/type-alias-impl-trait/issue-63355.stderr
new file mode 100644
index 0000000000000..dc5370a2666b7
--- /dev/null
+++ b/src/test/ui/type-alias-impl-trait/issue-63355.stderr
@@ -0,0 +1,14 @@
+error[E0271]: type mismatch resolving `<() as Bar>::Foo == ()`
+  --> $DIR/issue-63355.rs:34:20
+   |
+LL | pub type FooImpl = impl Foo;
+   |                    -------- the found opaque type
+LL | pub type BarImpl = impl Bar<Foo = FooImpl>;
+   |                    ^^^^^^^^^^^^^^^^^^^^^^^ expected `()`, found opaque type
+   |
+   = note: expected unit type `()`
+            found opaque type `impl Foo`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0271`.