add test for #102605

Author: Rageking8

src/test/ui/impl-trait/issue-102605.rs

@@ -0,0 +1,15 @@
+// edition:2021
+
+async fn foo() -> Result<(), String> {
+    Ok(())
+}
+
+fn convert_result<T, E>(r: Result<T, E>) -> Option<T> {
+    None
+}
+
+fn main() -> Option<()> {
+    //~^ ERROR `main` has invalid return type `Option<()>`
+    convert_result(foo())
+    //~^ ERROR mismatched types
+}

src/test/ui/impl-trait/issue-102605.stderr

@@ -0,0 +1,41 @@
+error[E0308]: mismatched types
+  --> $DIR/issue-102605.rs:13:20
+   |
+LL |     convert_result(foo())
+   |     -------------- ^^^^^ expected enum `Result`, found opaque type
+   |     |
+   |     arguments to this function are incorrect
+   |
+note: while checking the return type of the `async fn`
+  --> $DIR/issue-102605.rs:3:19
+   |
+LL | async fn foo() -> Result<(), String> {
+   |                   ^^^^^^^^^^^^^^^^^^ checked the `Output` of this `async fn`, found opaque type
+   = note:     expected enum `Result<(), _>`
+           found opaque type `impl Future<Output = Result<(), String>>`
+note: function defined here
+  --> $DIR/issue-102605.rs:7:4
+   |
+LL | fn convert_result<T, E>(r: Result<T, E>) -> Option<T> {
+   |    ^^^^^^^^^^^^^^       ---------------
+help: consider `await`ing on the `Future`
+   |
+LL |     convert_result(foo().await)
+   |                         ++++++
+help: try wrapping the expression in `Err`
+   |
+LL |     convert_result(Err(foo()))
+   |                    ++++     +
+
+error[E0277]: `main` has invalid return type `Option<()>`
+  --> $DIR/issue-102605.rs:11:14
+   |
+LL | fn main() -> Option<()> {
+   |              ^^^^^^^^^^ `main` can only return types that implement `Termination`
+   |
+   = help: consider using `()`, or a `Result`
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0277, E0308.
+For more information about an error, try `rustc --explain E0277`.