Add tests for lifetime-swaps, not just type param swaps

Author: oli-obk

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

@@ -0,0 +1,10 @@
+
+#![feature(type_alias_impl_trait)]
+
+type Foo<'a, 'b> = impl std::fmt::Debug;
+
+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() {}

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

@@ -0,0 +1,14 @@
+error: concrete type differs from previous defining opaque type use
+  --> $DIR/multiple-def-uses-in-one-fn-lifetimes.rs:6:1
+   |
+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
+   |
+LL | fn foo<'x, 'y>(i: &'x i32, j: &'y i32) -> (Foo<'x, 'y>, Foo<'y, 'x>) {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+

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

@@ -7,6 +7,15 @@ fn f<A: ToString + Clone, B: ToString + Clone>(a: A, b: B) -> (X<A, B>, X<A, B>)
     (a.clone(), a)
 }
 
+type Foo<'a, 'b> = impl std::fmt::Debug;
+
+fn foo<'x, 'y>(i: &'x i32, j: &'y i32) -> (Foo<'x, 'y>, Foo<'y, 'x>) {
+    (i, j)
+}
+
 fn main() {
     println!("{}", <X<_, _> as ToString>::to_string(&f(42_i32, String::new()).1));
+    let meh = 42;
+    let muh = 69;
+    println!("{:?}", foo(&meh, &muh));
 }