Add more tests

src/test/ui/lazy-type-alias-impl-trait/branches.rs

@@ -1,7 +1,5 @@
 #![feature(type_alias_impl_trait)]
 
-// check-pass
-
 type Foo = impl std::fmt::Debug;
 
 fn foo(b: bool) -> Foo {
@@ -12,4 +10,16 @@ fn foo(b: bool) -> Foo {
     }
 }
 
+type Bar = impl std::fmt::Debug;
+
+fn bar(b: bool) -> Bar {
+    let x: Bar = if b {
+        vec![42_i32]
+    } else {
+        std::iter::empty().collect()
+        //~^ ERROR  a value of type `Bar` cannot be built from an iterator over elements of type `_`
+    };
+    x
+}
+
 fn main() {}

src/test/ui/lazy-type-alias-impl-trait/branches.stderr

@@ -0,0 +1,16 @@
+error[E0277]: a value of type `Bar` cannot be built from an iterator over elements of type `_`
+  --> $DIR/branches.rs:19:28
+   |
+LL |         std::iter::empty().collect()
+   |                            ^^^^^^^ value of type `Bar` cannot be built from `std::iter::Iterator<Item=_>`
+   |
+   = help: the trait `FromIterator<_>` is not implemented for `Bar`
+note: required by a bound in `collect`
+  --> $SRC_DIR/core/src/iter/traits/iterator.rs:LL:COL
+   |
+LL |     fn collect<B: FromIterator<Self::Item>>(self) -> B
+   |                   ^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `collect`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.