macros: charecterization tests for ? operator fail

tests-build/tests/fail/macros_type_mismatch.rs

@@ -23,6 +23,40 @@ async fn extra_semicolon() -> Result<(), ()> {
     Ok(());
 }
 
+/// This test is a charecterization test for the `?` operator.
+///
+/// See <https://github.com/tokio-rs/tokio/issues/6930#issuecomment-2572502517> for more details.
+///
+/// It should fail with a single error message about the return type of the function, but instead
+/// if fails with an extra error message due to the `?` operator being used within the async block
+/// rather than the original function.
+///
+/// ```text
+/// 28 |     None?;
+///    |         ^ cannot use the `?` operator in an async block that returns `()`
+/// ```
+#[tokio::main]
+async fn question_mark_operator_with_invalid_option() -> Option<()> {
+    None?;
+}
+
+/// This test is a charecterization test for the `?` operator.
+///
+/// See <https://github.com/tokio-rs/tokio/issues/6930#issuecomment-2572502517> for more details.
+///
+/// It should fail with a single error message about the return type of the function, but instead
+/// if fails with an extra error message due to the `?` operator being used within the async block
+/// rather than the original function.
+///
+/// ```text
+/// 33 |     Ok(())?;
+///    |           ^ cannot use the `?` operator in an async block that returns `()`
+/// ```
+#[tokio::main]
+async fn question_mark_operator_with_invalid_result() -> Result<(), ()> {
+    Ok(())?;
+}
+
 // https://github.com/tokio-rs/tokio/issues/4635
 #[allow(redundant_semicolons)]
 #[rustfmt::skip]

tests-build/tests/fail/macros_type_mismatch.stderr

@@ -49,11 +49,68 @@ help: try adding an expression at the end of the block
 24 +     Ok(())
    |
 
+error[E0277]: the `?` operator can only be used in an async block that returns `Result` or `Option` (or another type that implements `FromResidual`)
+  --> tests/fail/macros_type_mismatch.rs:40:9
+   |
+38 | #[tokio::main]
+   | -------------- this function should return `Result` or `Option` to accept `?`
+39 | async fn question_mark_operator_with_invalid_option() -> Option<()> {
+40 |     None?;
+   |         ^ cannot use the `?` operator in an async block that returns `()`
+   |
+   = help: the trait `FromResidual<Option<Infallible>>` is not implemented for `()`
+
+error[E0308]: mismatched types
+  --> tests/fail/macros_type_mismatch.rs:40:5
+   |
+39 | async fn question_mark_operator_with_invalid_option() -> Option<()> {
+   |                                                          ---------- expected `Option<()>` because of return type
+40 |     None?;
+   |     ^^^^^^ expected `Option<()>`, found `()`
+   |
+   = note:   expected enum `Option<()>`
+           found unit type `()`
+help: try adding an expression at the end of the block
+   |
+40 ~     None?;;
+41 +     None
+   |
+40 ~     None?;;
+41 +     Some(())
+   |
+
+error[E0277]: the `?` operator can only be used in an async block that returns `Result` or `Option` (or another type that implements `FromResidual`)
+  --> tests/fail/macros_type_mismatch.rs:57:11
+   |
+55 | #[tokio::main]
+   | -------------- this function should return `Result` or `Option` to accept `?`
+56 | async fn question_mark_operator_with_invalid_result() -> Result<(), ()> {
+57 |     Ok(())?;
+   |           ^ cannot use the `?` operator in an async block that returns `()`
+   |
+   = help: the trait `FromResidual<Result<Infallible, _>>` is not implemented for `()`
+
+error[E0308]: mismatched types
+  --> tests/fail/macros_type_mismatch.rs:57:5
+   |
+56 | async fn question_mark_operator_with_invalid_result() -> Result<(), ()> {
+   |                                                          -------------- expected `Result<(), ()>` because of return type
+57 |     Ok(())?;
+   |     ^^^^^^^^ expected `Result<(), ()>`, found `()`
+   |
+   = note:   expected enum `Result<(), ()>`
+           found unit type `()`
+help: try adding an expression at the end of the block
+   |
+57 ~     Ok(())?;;
+58 +     Ok(())
+   |
+
 error[E0308]: mismatched types
-  --> tests/fail/macros_type_mismatch.rs:32:5
+  --> tests/fail/macros_type_mismatch.rs:66:5
    |
-30 | async fn issue_4635() {
+64 | async fn issue_4635() {
    |                      - help: try adding a return type: `-> i32`
-31 |     return 1;
-32 |     ;
+65 |     return 1;
+66 |     ;
    |     ^ expected `()`, found integer