Remove type parameter default from FromResidual.

Author: zachs18

library/core/src/ops/control_flow.rs

@@ -116,7 +116,9 @@ impl<B, C> ops::Try for ControlFlow<B, C> {
 }
 
 #[unstable(feature = "try_trait_v2", issue = "84277")]
-impl<B, C> ops::FromResidual for ControlFlow<B, C> {
+// Note: manually specifying the residual type instead of using the default to work around
+// https://github.com/rust-lang/rust/issues/99940
+impl<B, C> ops::FromResidual<ControlFlow<B, convert::Infallible>> for ControlFlow<B, C> {
     #[inline]
     fn from_residual(residual: ControlFlow<B, convert::Infallible>) -> Self {
         match residual {

library/core/src/option.rs

@@ -2495,7 +2495,9 @@ impl<T> ops::Try for Option<T> {
 }
 
 #[unstable(feature = "try_trait_v2", issue = "84277")]
-impl<T> ops::FromResidual for Option<T> {
+// Note: manually specifying the residual type instead of using the default to work around
+// https://github.com/rust-lang/rust/issues/99940
+impl<T> ops::FromResidual<Option<convert::Infallible>> for Option<T> {
     #[inline]
     fn from_residual(residual: Option<convert::Infallible>) -> Self {
         match residual {

tests/ui/try-trait/bad-interconversion.stderr

@@ -45,7 +45,7 @@ LL |     Some(Err("hello")?)
    |                      ^ use `.ok()?` if you want to discard the `Result<Infallible, &str>` error information
    |
    = help: the trait `FromResidual<Result<Infallible, &str>>` is not implemented for `Option<u16>`
-   = help: the trait `FromResidual` is implemented for `Option<T>`
+   = help: the trait `FromResidual<Option<Infallible>>` is implemented for `Option<T>`
 
 error[E0277]: the `?` operator can only be used on `Option`s in a function that returns `Option`
   --> $DIR/bad-interconversion.rs:27:33
@@ -56,7 +56,7 @@ LL |     Some(ControlFlow::Break(123)?)
    |                                 ^ this `?` produces `ControlFlow<{integer}, Infallible>`, which is incompatible with `Option<u64>`
    |
    = help: the trait `FromResidual<ControlFlow<{integer}, Infallible>>` is not implemented for `Option<u64>`
-   = help: the trait `FromResidual` is implemented for `Option<T>`
+   = help: the trait `FromResidual<Option<Infallible>>` is implemented for `Option<T>`
 
 error[E0277]: the `?` operator can only be used on `ControlFlow`s in a function that returns `ControlFlow`
   --> $DIR/bad-interconversion.rs:32:39

tests/ui/try-trait/option-to-result.stderr

@@ -20,7 +20,7 @@ LL |     a?;
    |      ^ use `.ok()?` if you want to discard the `Result<Infallible, i32>` error information
    |
    = help: the trait `FromResidual<Result<Infallible, i32>>` is not implemented for `Option<i32>`
-   = help: the trait `FromResidual` is implemented for `Option<T>`
+   = help: the trait `FromResidual<Option<Infallible>>` is implemented for `Option<T>`
 
 error: aborting due to 2 previous errors