Add Sizedness test

Author: adetaylor

tests/ui/self/arbitrary_self_types_sizedness_trait.rs

@@ -0,0 +1,25 @@
+#![feature(arbitrary_self_types)]
+
+struct SmartPtr<'a, T: ?Sized>(&'a T);
+
+// Easy mistake is to implement this for T not T: Sized
+impl<T> std::ops::Receiver for SmartPtr<'_, T> {
+    type Target = T;
+}
+
+struct A;
+
+trait B {
+    fn m(self: SmartPtr<Self>) {}
+    //~^ ERROR: invalid `self` parameter type
+}
+
+impl B for A {
+    fn m(self: SmartPtr<Self>) {}
+}
+
+fn main() {
+    let a = A;
+    let a = SmartPtr(&A);
+    a.m();
+}

tests/ui/self/arbitrary_self_types_sizedness_trait.stderr

@@ -0,0 +1,12 @@
+error[E0307]: invalid `self` parameter type: `SmartPtr<'_, Self>`
+  --> $DIR/arbitrary_self_types_sizedness_trait.rs:13:16
+   |
+LL |     fn m(self: SmartPtr<Self>) {}
+   |                ^^^^^^^^^^^^^^
+   |
+   = note: type of `self` must be `Self` or some type implementing `Receiver`
+   = help: consider changing to `self`, `&self`, `&mut self`, or a type implementing `Receiver` such as `self: Box<Self>`, `self: Rc<Self>`, or `self: Arc<Self>`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0307`.