add a ui test for Lazy{Cell,Lock} variance

Author: WaffleLapkin

tests/ui/variance/variance-library-types.rs

@@ -0,0 +1,11 @@
+// Check that certain library types have correct variance.
+#![feature(rustc_attrs)]
+
+
+#[rustc_dump_variances]
+struct LazyCellIsCovariantOnlyInF<T, F>(std::cell::LazyCell<T, F>); //~ ERROR [T: o, F: +]
+
+#[rustc_dump_variances]
+struct LazyLockIsCovariantOnlyInF<T, F>(std::sync::LazyLock<T, F>); //~ ERROR [T: o, F: +]
+
+pub fn main() {}

tests/ui/variance/variance-library-types.stderr

@@ -0,0 +1,14 @@
+error: [T: o, F: +]
+  --> $DIR/variance-library-types.rs:6:1
+   |
+LL | struct LazyCellIsCovariantOnlyInF<T, F>(std::cell::LazyCell<T, F>);
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: [T: o, F: +]
+  --> $DIR/variance-library-types.rs:9:1
+   |
+LL | struct LazyLockIsCovariantOnlyInF<T, F>(std::sync::LazyLock<T, F>);
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+