Add more tests

Author: oli-obk

src/tools/rustfmt/tests/source/trait.rs

@@ -181,3 +181,5 @@ trait Visible {
     pub fn f();
     pub fn g() {}
 }
+
+const trait Foomp = Hash;

src/tools/rustfmt/tests/target/trait.rs

@@ -218,3 +218,5 @@ trait Visible {
     pub fn f();
     pub fn g() {}
 }
+
+trait Foomp = Hash;

tests/ui/consts/trait_alias_method_call.rs

@@ -0,0 +1,31 @@
+//! Test that we do not need to handle host effects in `expand_trait_aliases`
+
+#![feature(trait_alias, const_trait_impl)]
+//@ check-pass
+
+mod foo {
+    pub const trait Bar {
+        fn bar(&self) {}
+    }
+    pub const trait Baz {
+        fn baz(&self) {}
+    }
+
+    impl const Bar for () {}
+    impl const Baz for () {}
+
+    pub const trait Foo = [const] Bar + Baz;
+}
+
+use foo::Foo as _;
+
+
+const _: () = {
+    // Ok via `[const] Bar` on `Foo`
+    ().bar();
+    // Also works, because everything is fully concrete, so we're ignoring that
+    // `Baz` is not a const trait bound of `Foo`.
+    ().baz();
+};
+
+fn main() {}