Rollup merge of rust-lang#51104 - zackmdavis:dynamo, r=nikomatsakis

add `dyn ` to display of dynamic (trait) types

~~I'm not sure we want the `dyn` in the E0277 "trait bound [...] is not satisfied" messages ("bound" sounds like a different thing in contrast to the names of specific trait-object types like `Box<dyn Trait>`), but I'm finding the code I would need to change that hard to follow—the [display object seems to](https://github.com/rust-lang/rust/blob/f0805a4421449bd6fe3096d63820fbebe2bfcd1d/src/librustc/traits/error_reporting.rs#L600) be a [`Predicate::Trait`](https://github.com/rust-lang/rust/blob/f0805a4421449bd6fe3096d63820fbebe2bfcd1d/src/librustc/ty/mod.rs#L962) variant, whose [`Display` implementation](https://github.com/rust-lang/rust/blob/f0805a4421449bd6fe3096d63820fbebe2bfcd1d/src/librustc/util/ppaux.rs#L1309) calls `.print` on its `PolyTraitPredicate` member, [which is a type alias](https://github.com/rust-lang/rust/blob/f0805a4421449bd6fe3096d63820fbebe2bfcd1d/src/librustc/ty/mod.rs#L1112) for `ty::Binder<TraitPredicate<'tcx>>`, whose [`Display` implementation](https://github.com/rust-lang/rust/blob/f0805a4421449bd6fe3096d63820fbebe2bfcd1d/src/librustc/util/ppaux.rs#L975-L985) ... _&c._— so maybe it's time to pull-request this and see what reviewers think.~~

 Resolves rust-lang#49277 (?).

r? @nikomatsakis

Author: pietroalbini

src/librustc/util/ppaux.rs

@@ -1062,10 +1062,14 @@ define_print! {
                 TyParam(ref param_ty) => write!(f, "{}", param_ty),
                 TyAdt(def, substs) => cx.parameterized(f, substs, def.did, &[]),
                 TyDynamic(data, r) => {
-                    data.print(f, cx)?;
                     let r = r.print_to_string(cx);
                     if !r.is_empty() {
-                        write!(f, " + {}", r)
+                        write!(f, "(")?;
+                    }
+                    write!(f, "dyn ")?;
+                    data.print(f, cx)?;
+                    if !r.is_empty() {
+                        write!(f, " + {})", r)
                     } else {
                         Ok(())
                     }

src/test/compile-fail/cross-borrow-trait.rs

@@ -18,6 +18,6 @@ impl Trait for Foo {}
 pub fn main() {
     let x: Box<Trait> = Box::new(Foo);
     let _y: &Trait = x; //~ ERROR E0308
-                        //~| expected type `&Trait`
-                        //~| found type `std::boxed::Box<Trait>`
+                        //~| expected type `&dyn Trait`
+                        //~| found type `std::boxed::Box<dyn Trait>`
 }

src/test/compile-fail/destructure-trait-ref.rs

@@ -33,23 +33,23 @@ fn main() {
     let &&x = &&(&1isize as &T);
 
     // n == m
-    let &x = &1isize as &T;      //~ ERROR type `&T` cannot be dereferenced
-    let &&x = &(&1isize as &T);  //~ ERROR type `&T` cannot be dereferenced
-    let box x = box 1isize as Box<T>; //~ ERROR type `std::boxed::Box<T>` cannot be dereferenced
+    let &x = &1isize as &T;      //~ ERROR type `&dyn T` cannot be dereferenced
+    let &&x = &(&1isize as &T);  //~ ERROR type `&dyn T` cannot be dereferenced
+    let box x = box 1isize as Box<T>; //~ ERROR type `std::boxed::Box<dyn T>` cannot be dereferenced
 
     // n > m
     let &&x = &1isize as &T;
     //~^ ERROR mismatched types
-    //~| expected type `T`
+    //~| expected type `dyn T`
     //~| found type `&_`
     //~| expected trait T, found reference
     let &&&x = &(&1isize as &T);
     //~^ ERROR mismatched types
-    //~| expected type `T`
+    //~| expected type `dyn T`
     //~| found type `&_`
     //~| expected trait T, found reference
     let box box x = box 1isize as Box<T>;
     //~^ ERROR mismatched types
-    //~| expected type `T`
+    //~| expected type `dyn T`
     //~| found type `std::boxed::Box<_>`
 }

src/test/compile-fail/dst-bad-assign-3.rs

@@ -42,7 +42,7 @@ pub fn main() {
     let z: Box<ToBar> = Box::new(Bar1 {f: 36});
     f5.2 = Bar1 {f: 36};
     //~^ ERROR mismatched types
-    //~| expected type `ToBar`
+    //~| expected type `dyn ToBar`
     //~| found type `Bar1`
     //~| expected trait ToBar, found struct `Bar1`
     //~| ERROR the size for value values of type

src/test/compile-fail/dst-bad-assign.rs

@@ -44,7 +44,7 @@ pub fn main() {
     let z: Box<ToBar> = Box::new(Bar1 {f: 36});
     f5.ptr = Bar1 {f: 36};
     //~^ ERROR mismatched types
-    //~| expected type `ToBar`
+    //~| expected type `dyn ToBar`
     //~| found type `Bar1`
     //~| expected trait ToBar, found struct `Bar1`
     //~| ERROR the size for value values of type

src/test/compile-fail/fn-trait-formatting.rs

@@ -16,15 +16,15 @@ fn main() {
     let _: () = (box |_: isize| {}) as Box<FnOnce(isize)>;
     //~^ ERROR mismatched types
     //~| expected type `()`
-    //~| found type `std::boxed::Box<std::ops::FnOnce(isize)>`
+    //~| found type `std::boxed::Box<dyn std::ops::FnOnce(isize)>`
     let _: () = (box |_: isize, isize| {}) as Box<Fn(isize, isize)>;
     //~^ ERROR mismatched types
     //~| expected type `()`
-    //~| found type `std::boxed::Box<std::ops::Fn(isize, isize)>`
+    //~| found type `std::boxed::Box<dyn std::ops::Fn(isize, isize)>`
     let _: () = (box || -> isize { unimplemented!() }) as Box<FnMut() -> isize>;
     //~^ ERROR mismatched types
     //~| expected type `()`
-    //~| found type `std::boxed::Box<std::ops::FnMut() -> isize>`
+    //~| found type `std::boxed::Box<dyn std::ops::FnMut() -> isize>`
 
     needs_fn(1);
     //~^ ERROR : std::ops::Fn<(isize,)>`

src/test/compile-fail/issue-13033.rs

@@ -17,8 +17,8 @@ struct Baz;
 impl Foo for Baz {
     fn bar(&mut self, other: &Foo) {}
     //~^ ERROR method `bar` has an incompatible type for trait
-    //~| expected type `fn(&mut Baz, &mut Foo)`
-    //~| found type `fn(&mut Baz, &Foo)`
+    //~| expected type `fn(&mut Baz, &mut dyn Foo)`
+    //~| found type `fn(&mut Baz, &dyn Foo)`
 }
 
 fn main() {}

src/test/compile-fail/issue-20939.rs

@@ -11,6 +11,6 @@
 trait Foo {}
 
 impl<'a> Foo for Foo+'a {}
-//~^ ERROR the object type `Foo + 'a` automatically implements the trait `Foo`
+//~^ ERROR the object type `(dyn Foo + 'a)` automatically implements the trait `Foo`
 
 fn main() {}

src/test/compile-fail/issue-32963.rs

@@ -17,5 +17,5 @@ fn size_of_copy<T: Copy+?Sized>() -> usize { mem::size_of::<T>() }
 fn main() {
     size_of_copy::<Misc+Copy>();
     //~^ ERROR only auto traits can be used as additional traits in a trait object
-    //~| ERROR the trait bound `Misc: std::marker::Copy` is not satisfied
+    //~| ERROR the trait bound `dyn Misc: std::marker::Copy` is not satisfied
 }

src/test/compile-fail/issue-41139.rs

@@ -14,5 +14,5 @@ fn get_function<'a>() -> &'a Fn() -> Trait { panic!("") }
 
 fn main() {
     let t : &Trait = &get_function()();
-    //~^ ERROR cannot move a value of type Trait + 'static
+    //~^ ERROR cannot move a value of type (dyn Trait + 'static)
 }