Arbitrary self types: tests for 'mismatched types'

Adding tests for cases where diagnostics aren't as good as they should
be in the case of arbitrary self types.

These are slightly duplicative of the existing
arbitrary-self-from-method-substs.rs
test, but test more permutations so it seems worth adding to the
coverage as we explore improving the diagnostics here.

Improved diagnostics were suggested in commit 05c5caa

This is a part of the arbitrary self types v2 project,
rust-lang/rfcs#3519
and specifically the sub-issue exploring questions around
generics,
#129147

tests/ui/self/arbitrary-self-from-method-substs-no-turbofish.default.stderr

@@ -0,0 +1,29 @@
+error[E0658]: `<FR as FindReceiver>::Receiver` cannot be used as the type of `self` without the `arbitrary_self_types` feature
+  --> $DIR/arbitrary-self-from-method-substs-no-turbofish.rs:13:36
+   |
+LL |     fn get<FR: FindReceiver>(self: FR::Receiver, other: FR) -> u32 {
+   |                                    ^^^^^^^^^^^^
+   |
+   = note: see issue #44874 <https://github.com/rust-lang/rust/issues/44874> for more information
+   = help: add `#![feature(arbitrary_self_types)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+   = help: consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one of the previous types except `Self`)
+
+error[E0271]: type mismatch resolving `<Silly as FindReceiver>::Receiver == Foo`
+  --> $DIR/arbitrary-self-from-method-substs-no-turbofish.rs:36:9
+   |
+LL |     foo.get(Silly);
+   |         ^^^ type mismatch resolving `<Silly as FindReceiver>::Receiver == Foo`
+   |
+note: expected this to be `SmartPtr<Foo>`
+  --> $DIR/arbitrary-self-from-method-substs-no-turbofish.rs:29:21
+   |
+LL |     type Receiver = SmartPtr<Foo>;
+   |                     ^^^^^^^^^^^^^
+   = note: expected struct `SmartPtr<Foo>`
+              found struct `Foo`
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0271, E0658.
+For more information about an error, try `rustc --explain E0271`.

tests/ui/self/arbitrary-self-from-method-substs-no-turbofish.feature.stderr

@@ -0,0 +1,17 @@
+error[E0271]: type mismatch resolving `<Silly as FindReceiver>::Receiver == Foo`
+  --> $DIR/arbitrary-self-from-method-substs-no-turbofish.rs:36:9
+   |
+LL |     foo.get(Silly);
+   |         ^^^ type mismatch resolving `<Silly as FindReceiver>::Receiver == Foo`
+   |
+note: expected this to be `SmartPtr<Foo>`
+  --> $DIR/arbitrary-self-from-method-substs-no-turbofish.rs:29:21
+   |
+LL |     type Receiver = SmartPtr<Foo>;
+   |                     ^^^^^^^^^^^^^
+   = note: expected struct `SmartPtr<Foo>`
+              found struct `Foo`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0271`.

tests/ui/self/arbitrary-self-from-method-substs-no-turbofish.rs

@@ -0,0 +1,38 @@
+//@ revisions: default feature
+#![cfg_attr(feature, feature(arbitrary_self_types))]
+
+use std::ops::Deref;
+use std::marker::PhantomData;
+
+trait FindReceiver {
+    type Receiver: Deref<Target = Foo>;
+}
+
+struct Foo(u32);
+impl Foo {
+    fn get<FR: FindReceiver>(self: FR::Receiver, other: FR) -> u32 {
+        //[default]~^ ERROR: `<FR as FindReceiver>::Receiver` cannot be used as the type of `self`
+        42
+    }
+}
+
+struct SmartPtr<T>(T);
+impl<T> Deref for SmartPtr<T> {
+    type Target = T;
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+struct Silly;
+impl FindReceiver for Silly {
+    type Receiver = SmartPtr<Foo>;
+}
+
+fn main() {
+    let mut foo = Foo(1);
+    // This test is slightly contrived in an attempt to generate a mismatched types
+    // error for the self type below, without using the turbofish.
+    foo.get(Silly);
+    //~^ ERROR type mismatch
+}

tests/ui/self/arbitrary_self_types_mismatched.rs

@@ -0,0 +1,38 @@
+#![feature(arbitrary_self_types)]
+
+use std::ops::Deref;
+
+struct SmartPtr<'a, T: ?Sized>(&'a T);
+
+impl<'a, T: ?Sized> Deref for SmartPtr<'a, T> {
+    type Target = T;
+    fn deref(&self) -> &Self::Target {
+        unimplemented!()
+    }
+}
+
+struct SmartPtr2<'a, T: ?Sized>(&'a T);
+
+impl<'a, T: ?Sized> Deref for SmartPtr2<'a, T> {
+    type Target = T;
+    fn deref(&self) -> &Self::Target {
+        unimplemented!()
+    }
+}
+
+
+struct Foo(u32);
+impl Foo {
+    fn a<R: Deref<Target=Self>>(self: R) { }
+}
+
+fn main() {
+    let foo = Foo(1);
+    let smart_ptr = SmartPtr(&foo);
+    let smart_ptr2 = SmartPtr2(&foo);
+    smart_ptr.a(); // this compiles
+    smart_ptr.a::<SmartPtr2<Foo>>();
+    //~^ ERROR mismatched types
+    smart_ptr.a::<&Foo>();
+    //~^ ERROR mismatched types
+}