tests: add variance test for const traits

Added to demonstrate change in output in following commit. Many more
interesting tests change with different output, missing errors, new
errors, etc related to this but they all depend on feature flags and
are much more complex than this.

2 files changed, 22 insertions, 0 deletions

diff --git a/tests/ui/traits/const-traits/variance.rs b/tests/ui/traits/const-traits/variance.rs
new file mode 100644
index 00000000000..9eaf7910cb8
--- /dev/null
+++ b/tests/ui/traits/const-traits/variance.rs
@@ -0,0 +1,14 @@
+#![feature(rustc_attrs, const_trait_impl)]
+#![allow(internal_features)]
+#![rustc_variance_of_opaques]
+
+#[const_trait]
+trait Foo {}
+
+impl const Foo for () {}
+
+fn foo<'a: 'a>() -> impl const Foo {}
+//~^ ERROR ['a: o]
+
+fn main() {}
+
diff --git a/tests/ui/traits/const-traits/variance.stderr b/tests/ui/traits/const-traits/variance.stderr
new file mode 100644
index 00000000000..f6efc24b747
--- /dev/null
+++ b/tests/ui/traits/const-traits/variance.stderr
@@ -0,0 +1,8 @@
+error: ['a: o]
+  --> $DIR/variance.rs:10:21
+   |
+LL | fn foo<'a: 'a>() -> impl const Foo {}
+   |                     ^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+