Add ui tests that were unsound previously and now fail on downcast_trait().unwrap() as expected

Author: ivarflakstad

tests/ui/any/downcast_trait_err1.rs

@@ -0,0 +1,30 @@
+//@ run-pass
+#![feature(downcast_trait)]
+
+use std::{any::downcast_trait, sync::OnceLock};
+
+trait Trait {
+    fn call(&self, x: &Box<i32>);
+}
+
+impl Trait for for<'a> fn(&'a Box<i32>) {
+    fn call(&self, x: &Box<i32>) {
+        self(x);
+    }
+}
+
+static STORAGE: OnceLock<&'static Box<i32>> = OnceLock::new();
+
+fn store(x: &'static Box<i32>) {
+    STORAGE.set(x).unwrap();
+}
+
+fn main() {
+    let data = Box::new(Box::new(1i32));
+    let fn_ptr: fn(&'static Box<i32>) = store;
+    downcast_trait::<_, dyn Trait>(&fn_ptr)
+        .unwrap()
+        .call(&*data);
+    drop(data);
+    println!("{}", STORAGE.get().unwrap());
+}

tests/ui/any/downcast_trait_err2.rs

@@ -0,0 +1,28 @@
+//@ run-pass
+#![feature(downcast_trait)]
+use std::{any::downcast_trait, sync::OnceLock};
+
+trait Trait<T> {
+    fn call(&self, t: T, x: &Box<i32>);
+}
+
+impl Trait<for<'a> fn(&'a Box<i32>)> for () {
+    fn call(&self, f: for<'a> fn(&'a Box<i32>), x: &Box<i32>) {
+        f(x);
+    }
+}
+
+static STORAGE: OnceLock<&'static Box<i32>> = OnceLock::new();
+
+fn store(x: &'static Box<i32>) {
+    STORAGE.set(x).unwrap();
+}
+
+fn main() {
+    let data = Box::new(Box::new(1i32));
+    downcast_trait::<_, dyn Trait<fn(&'static Box<i32>)>>(&())
+        .unwrap()
+        .call(store, &*data);
+    drop(data);
+    println!("{}", STORAGE.get().unwrap());
+}