add some fun tests

Author: lcnr

src/test/ui/lifetimes/re-empty-in-error.rs

@@ -0,0 +1,10 @@
+// We didn't have a single test mentioning
+// `ReEmpty` and this test changes that.
+fn foo<'a>(_a: &'a u32) where for<'b> &'b (): 'a {
+    //~^ NOTE type must outlive the empty lifetime as required by this binding
+}
+
+fn main() {
+    foo(&10);
+    //~^ ERROR the type `&'b ()` does not fulfill the required lifetime
+}

src/test/ui/lifetimes/re-empty-in-error.stderr

@@ -0,0 +1,15 @@
+error[E0477]: the type `&'b ()` does not fulfill the required lifetime
+  --> $DIR/re-empty-in-error.rs:8:5
+   |
+LL |     foo(&10);
+   |     ^^^
+   |
+note: type must outlive the empty lifetime as required by this binding
+  --> $DIR/re-empty-in-error.rs:3:47
+   |
+LL | fn foo<'a>(_a: &'a u32) where for<'b> &'b (): 'a {
+   |                                               ^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0477`.

src/test/ui/nll/user-annotations/issue-57280-1-flipped.rs

@@ -0,0 +1,23 @@
+// This test should compile, as the lifetimes
+// in matches don't really matter.
+//
+// We currently use contravariance when checking the
+// type of match arms.
+
+trait Foo<'a> {
+    const C: &'a u32;
+}
+
+impl<'a, T> Foo<'a> for T {
+    const C: &'a u32 = &22;
+}
+
+fn foo<'a>(x: &'static u32) {
+    match x {
+        <() as Foo<'a>>::C => { }
+        //~^ ERROR lifetime may not live long enough
+        &_ => { }
+    }
+}
+
+fn main() {}

src/test/ui/nll/user-annotations/issue-57280-1-flipped.stderr

@@ -0,0 +1,11 @@
+error: lifetime may not live long enough
+  --> $DIR/issue-57280-1-flipped.rs:17:9
+   |
+LL | fn foo<'a>(x: &'static u32) {
+   |        -- lifetime `'a` defined here
+LL |     match x {
+LL |         <() as Foo<'a>>::C => { }
+   |         ^^^^^^^^^^^^^^^^^^ type annotation requires that `'a` must outlive `'static`
+
+error: aborting due to previous error
+