Start using #[diagnostic::do_not_recommend] in the standard library

This commit starts using `#[diagnostic::do_not_recommend]` in the
standard library to improve some error messages. In this case we just
hide a certain nightly only impl as suggested in #121521

library/core/src/lib.rs

@@ -165,6 +165,7 @@
 #![feature(const_unsafecell_get_mut)]
 #![feature(const_waker)]
 #![feature(coverage_attribute)]
+#![feature(do_not_recommend)]
 #![feature(duration_consts_float)]
 #![feature(internal_impls_macro)]
 #![feature(ip)]

library/core/src/option.rs

@@ -2507,6 +2507,7 @@ impl<T> ops::FromResidual for Option<T> {
     }
 }
 
+#[diagnostic::do_not_recommend]
 #[unstable(feature = "try_trait_v2_yeet", issue = "96374")]
 impl<T> ops::FromResidual<ops::Yeet<()>> for Option<T> {
     #[inline]

library/core/src/result.rs

@@ -1990,7 +1990,7 @@ impl<T, E, F: From<E>> ops::FromResidual<Result<convert::Infallible, E>> for Res
         }
     }
 }
-
+#[diagnostic::do_not_recommend]
 #[unstable(feature = "try_trait_v2_yeet", issue = "96374")]
 impl<T, E, F: From<E>> ops::FromResidual<ops::Yeet<E>> for Result<T, F> {
     #[inline]

tests/ui/diagnostic_namespace/do_not_recommend/do_not_recommend_nightly_types.rs

@@ -0,0 +1,17 @@
+struct BarError;
+
+fn bar() -> Result<(), BarError> {
+    Ok(())
+}
+
+struct FooError;
+
+fn foo() -> Result<(), FooError> {
+    bar()?;
+    //~^ ERROR `?` couldn't convert the error to `FooError`
+    Ok(())
+}
+
+fn main() {
+    foo();
+}

tests/ui/diagnostic_namespace/do_not_recommend/do_not_recommend_nightly_types.stderr

@@ -0,0 +1,17 @@
+error[E0277]: `?` couldn't convert the error to `FooError`
+  --> $DIR/do_not_recommend_nightly_types.rs:10:10
+   |
+LL | fn foo() -> Result<(), FooError> {
+   |             -------------------- expected `FooError` because of this
+LL |     bar()?;
+   |     -----^ the trait `From<BarError>` is not implemented for `FooError`, which is required by `Result<(), FooError>: FromResidual<Result<Infallible, BarError>>`
+   |     |
+   |     this can't be annotated with `?` because it has type `Result<_, BarError>`
+   |
+   = note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait
+   = help: the trait `FromResidual<Result<Infallible, E>>` is implemented for `Result<T, F>`
+   = note: required for `Result<(), FooError>` to implement `FromResidual<Result<Infallible, BarError>>`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0277`.