Add some new tests with amusing diagnostics

src/test/ui/type-alias-impl-trait/multiple-def-uses-in-one-fn-lifetimes.rs

@@ -1,4 +1,3 @@
-
 #![feature(type_alias_impl_trait)]
 
 type Foo<'a, 'b> = impl std::fmt::Debug;
@@ -7,4 +6,4 @@ fn foo<'x, 'y>(i: &'x i32, j: &'y i32) -> (Foo<'x, 'y>, Foo<'y, 'x>) {
     (i, i) //~^ ERROR concrete type differs from previous
 }
 
-fn main() {}
+fn main() {}

src/test/ui/type-alias-impl-trait/multiple-def-uses-in-one-fn-lifetimes.stderr

@@ -1,11 +1,11 @@
 error: concrete type differs from previous defining opaque type use
-  --> $DIR/multiple-def-uses-in-one-fn-lifetimes.rs:6:1
+  --> $DIR/multiple-def-uses-in-one-fn-lifetimes.rs:5:1
    |
 LL | fn foo<'x, 'y>(i: &'x i32, j: &'y i32) -> (Foo<'x, 'y>, Foo<'y, 'x>) {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `&'a i32`, got `&'b i32`
    |
 note: previous use here
-  --> $DIR/multiple-def-uses-in-one-fn-lifetimes.rs:6:1
+  --> $DIR/multiple-def-uses-in-one-fn-lifetimes.rs:5:1
    |
 LL | fn foo<'x, 'y>(i: &'x i32, j: &'y i32) -> (Foo<'x, 'y>, Foo<'y, 'x>) {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

src/test/ui/type-alias-impl-trait/nested.rs

@@ -0,0 +1,17 @@
+#![feature(type_alias_impl_trait)]
+
+type Foo = impl std::fmt::Debug;
+type Bar = impl Trait<Foo>;
+
+trait Trait<T> {}
+
+impl<T, U> Trait<T> for U {}
+
+fn bar() -> Bar {
+    42
+}
+
+fn main() {
+    println!("{:?}", bar());
+    //~^ ERROR `impl Trait<Opaque(DefId(0:4 ~ nested[14f6]::Foo::{opaque#0}), [])>` doesn't implement `Debug`
+}

src/test/ui/type-alias-impl-trait/nested.stderr

@@ -0,0 +1,12 @@
+error[E0277]: `impl Trait<Opaque(DefId(0:4 ~ nested[14f6]::Foo::{opaque#0}), [])>` doesn't implement `Debug`
+  --> $DIR/nested.rs:15:22
+   |
+LL |     println!("{:?}", bar());
+   |                      ^^^^^ `impl Trait<Opaque(DefId(0:4 ~ nested[14f6]::Foo::{opaque#0}), [])>` cannot be formatted using `{:?}` because it doesn't implement `Debug`
+   |
+   = help: the trait `Debug` is not implemented for `impl Trait<Opaque(DefId(0:4 ~ nested[14f6]::Foo::{opaque#0}), [])>`
+   = note: this error originates in the macro `$crate::format_args_nl` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.

src/test/ui/type-alias-impl-trait/self-referential-2.rs

@@ -0,0 +1,10 @@
+#![feature(type_alias_impl_trait)]
+
+type Foo = impl std::fmt::Debug;
+type Bar = impl PartialEq<Foo>;
+
+fn bar() -> Bar {
+    42_i32 //~ ERROR can't compare `i32` with `impl Debug`
+}
+
+fn main() {}

src/test/ui/type-alias-impl-trait/self-referential-2.stderr

@@ -0,0 +1,11 @@
+error[E0277]: can't compare `i32` with `impl Debug`
+  --> $DIR/self-referential-2.rs:7:5
+   |
+LL |     42_i32
+   |     ^^^^^^ no implementation for `i32 == impl Debug`
+   |
+   = help: the trait `PartialEq<impl Debug>` is not implemented for `i32`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.

src/test/ui/type-alias-impl-trait/self-referential-3.rs

@@ -0,0 +1,14 @@
+// run-pass
+#![feature(type_alias_impl_trait)]
+
+type Bar<'a, 'b> = impl PartialEq<Bar<'a, 'b>> + std::fmt::Debug;
+
+fn bar<'a, 'b>(i: &'a i32) -> Bar<'a, 'b> {
+    i
+}
+
+fn main() {
+    let meh = 42;
+    let muh = 42;
+    assert_eq!(bar(&meh), bar(&muh));
+}

src/test/ui/type-alias-impl-trait/self-referential.rs

@@ -0,0 +1,13 @@
+#![feature(type_alias_impl_trait)]
+
+type Bar<'a, 'b> = impl PartialEq<Bar<'b, 'a>> + std::fmt::Debug;
+
+fn bar<'a, 'b>(i: &'a i32) -> Bar<'a, 'b> {
+    i //~ ERROR can't compare `&i32` with `impl PartialEq<Opaque
+}
+
+fn main() {
+    let meh = 42;
+    let muh = 69;
+    assert_eq!(bar(&meh), bar(&meh));
+}

src/test/ui/type-alias-impl-trait/self-referential.stderr

@@ -0,0 +1,11 @@
+error[E0277]: can't compare `&i32` with `impl PartialEq<Opaque(DefId(0:6 ~ self_referential[5b7d]::Bar::{opaque#0}), [ReFree(DefId(0:7 ~ self_referential[5b7d]::bar), BrNamed(DefId(0:8 ~ self_referential[5b7d]::bar::'a), 'a)), ReEarlyBound(0, 'b)])> + Debug`
+  --> $DIR/self-referential.rs:6:5
+   |
+LL |     i
+   |     ^ no implementation for `&i32 == impl PartialEq<Opaque(DefId(0:6 ~ self_referential[5b7d]::Bar::{opaque#0}), [ReFree(DefId(0:7 ~ self_referential[5b7d]::bar), BrNamed(DefId(0:8 ~ self_referential[5b7d]::bar::'a), 'a)), ReEarlyBound(0, 'b)])> + Debug`
+   |
+   = help: the trait `PartialEq<impl PartialEq<Opaque(DefId(0:6 ~ self_referential[5b7d]::Bar::{opaque#0}), [ReFree(DefId(0:7 ~ self_referential[5b7d]::bar), BrNamed(DefId(0:8 ~ self_referential[5b7d]::bar::'a), 'a)), ReEarlyBound(0, 'b)])> + Debug>` is not implemented for `&i32`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.