Allow dropping dyn principal

tests/ui/impl-trait/unsized_coercion5.next.stderr

@@ -1,14 +0,0 @@
-error[E0308]: mismatched types
-  --> $DIR/unsized_coercion5.rs:16:32
-   |
-LL |         let y: Box<dyn Send> = x as Box<dyn Trait + Send>;
-   |                -------------   ^^^^^^^^^^^^^^^^^^^^^^^^^^ expected trait `Send`, found trait `Trait + Send`
-   |                |
-   |                expected due to this
-   |
-   = note: expected struct `Box<dyn Send>`
-              found struct `Box<dyn Trait + Send>`
-
-error: aborting due to 1 previous error
-
-For more information about this error, try `rustc --explain E0308`.

tests/ui/impl-trait/unsized_coercion5.old.stderr

@@ -1,16 +1,5 @@
-error[E0308]: mismatched types
-  --> $DIR/unsized_coercion5.rs:16:32
-   |
-LL |         let y: Box<dyn Send> = x as Box<dyn Trait + Send>;
-   |                -------------   ^^^^^^^^^^^^^^^^^^^^^^^^^^ expected trait `Send`, found trait `Trait + Send`
-   |                |
-   |                expected due to this
-   |
-   = note: expected struct `Box<dyn Send>`
-              found struct `Box<dyn Trait + Send>`
-
 error[E0277]: the size for values of type `impl Trait + ?Sized` cannot be known at compilation time
-  --> $DIR/unsized_coercion5.rs:16:32
+  --> $DIR/unsized_coercion5.rs:17:32
    |
 LL |         let y: Box<dyn Send> = x as Box<dyn Trait + Send>;
    |                                ^ doesn't have a size known at compile-time
@@ -18,7 +7,6 @@ LL |         let y: Box<dyn Send> = x as Box<dyn Trait + Send>;
    = help: the trait `Sized` is not implemented for `impl Trait + ?Sized`
    = note: required for the cast from `Box<impl Trait + ?Sized>` to `Box<dyn Trait + Send>`
 
-error: aborting due to 2 previous errors
+error: aborting due to 1 previous error
 
-Some errors have detailed explanations: E0277, E0308.
-For more information about an error, try `rustc --explain E0277`.
+For more information about this error, try `rustc --explain E0277`.

tests/ui/impl-trait/unsized_coercion5.rs

@@ -3,6 +3,7 @@
 
 //@ revisions: next old
 //@[next] compile-flags: -Znext-solver
+//@[next] check-pass
 
 #![feature(trait_upcasting)]
 
@@ -15,7 +16,6 @@ fn hello() -> Box<impl Trait + ?Sized> {
         let x = hello();
         let y: Box<dyn Send> = x as Box<dyn Trait + Send>;
         //[old]~^ ERROR: the size for values of type `impl Trait + ?Sized` cannot be know
-        //~^^ ERROR: mismatched types
     }
     Box::new(1u32)
 }

tests/ui/traits/dyn-drop-principal.rs

@@ -0,0 +1,62 @@
+//@ run-pass
+//@ check-run-results
+
+use std::any::Any;
+
+const fn yeet_principal(x: Box<dyn Any + Send>) -> Box<dyn Send> {
+    x
+}
+
+trait Bar: Send + Sync {}
+
+impl<T: Send + Sync> Bar for T {}
+
+const fn yeet_principal_2(x: Box<dyn Bar>) -> Box<dyn Send> {
+    x
+}
+
+struct CallMe<F: FnOnce()>(Option<F>);
+
+impl<F: FnOnce()> CallMe<F> {
+    fn new(f: F) -> Self {
+        CallMe(Some(f))
+    }
+}
+
+impl<F: FnOnce()> Drop for CallMe<F> {
+    fn drop(&mut self) {
+        (self.0.take().unwrap())();
+    }
+}
+
+fn goodbye() {
+    println!("goodbye");
+}
+
+fn main() {
+    let x = Box::new(CallMe::new(goodbye)) as Box<dyn Any + Send>;
+    let y = yeet_principal(x);
+    println!("before");
+    drop(y);
+
+    let x = Box::new(CallMe::new(goodbye)) as Box<dyn Bar>;
+    let y = yeet_principal_2(x);
+    println!("before");
+    drop(y);
+}
+
+// Test that upcast works in `const`
+
+const fn yeet_principal_3(x: &(dyn Any + Send + Sync)) -> &(dyn Send + Sync) {
+    x
+}
+
+#[used]
+pub static FOO: &(dyn Send + Sync) = yeet_principal_3(&false);
+
+const fn yeet_principal_4(x: &dyn Bar) -> &(dyn Send + Sync) {
+    x
+}
+
+#[used]
+pub static BAR: &(dyn Send + Sync) = yeet_principal_4(&false);

tests/ui/traits/dyn-drop-principal.run.stdout

@@ -0,0 +1,4 @@
+before
+goodbye
+before
+goodbye