Drop use of unstable try_trait_v2 feature

It seems like there's still a fair amount of discussion around what the
Try API should look like in the tracking issue for try_trait_v2. This
could lead to the API being changed in the nightly compiler, and
breaking uefi-rs compilation (which is particularly annoying when using
a released version rather than the latest git version).

To avoid that possibility, just drop the feature as it is not much used
in uefi-rs and can easily be replaced. As described in the changelog,
most uses can be fixed by adding a call to `into()`. If the compiler
needs a bit more help, `Result::from(status)` can be used.

rust-osdev#452

CHANGELOG.md

@@ -39,6 +39,10 @@
   other than 1. A safe alternative is to use
   [`Vec::into_boxed_slice`](https://doc.rust-lang.org/std/vec/struct.Vec.html#method.into_boxed_slice).
 - Removed `From` conversions from `ucs2::Error` to `Status` and `Error`.
+- Removed use of the unstable `try_trait_v2` feature, which allowed `?`
+  to be used with `Status` in a function returning `uefi::Result`. This
+  can be replaced by calling `status.into()`, or `Result::from(status)`
+  in cases where the compiler needs a type hint.
 
 ## uefi-macros - [Unreleased]
 

src/lib.rs

@@ -23,7 +23,6 @@
 //! For example, a PC with no network card might not contain a network driver,
 //! therefore all the network protocols will be unavailable.
 
-#![feature(try_trait_v2)]
 #![feature(abi_efiapi)]
 #![feature(maybe_uninit_slice)]
 #![feature(negative_impls)]

src/proto/shim/mod.rs

@@ -108,14 +108,14 @@ impl ShimLock {
             .map_err(|_| Error::from(Status::BAD_BUFFER_SIZE))?;
 
         let mut context = MaybeUninit::<Context>::uninit();
-        (self.context)(ptr, size, context.as_mut_ptr())?;
+        Result::from((self.context)(ptr, size, context.as_mut_ptr()))?;
         (self.hash)(
             ptr,
             size,
             context.as_mut_ptr(),
             &mut hashes.sha256,
             &mut hashes.sha1,
-        )?;
-        Ok(())
+        )
+        .into()
     }
 }

src/result/status.rs

@@ -1,9 +1,5 @@
 use super::{Error, Result};
-use core::{
-    convert::Infallible,
-    ops::{ControlFlow, FromResidual, Try},
-};
-use core::{fmt::Debug, num::NonZeroUsize};
+use core::fmt::Debug;
 
 /// Bit indicating that an UEFI status code is an error
 const ERROR_BIT: usize = 1 << (core::mem::size_of::<usize>() * 8 - 1);
@@ -172,45 +168,6 @@ impl From<Status> for Result<(), ()> {
     }
 }
 
-pub struct StatusResidual(NonZeroUsize);
-
-impl Try for Status {
-    type Output = ();
-    type Residual = StatusResidual;
-
-    fn branch(self) -> ControlFlow<Self::Residual, Self::Output> {
-        match NonZeroUsize::new(self.0) {
-            Some(r) => ControlFlow::Break(StatusResidual(r)),
-            None => ControlFlow::Continue(()),
-        }
-    }
-
-    fn from_output(_output: Self::Output) -> Self {
-        Self::SUCCESS
-    }
-}
-
-impl FromResidual for Status {
-    fn from_residual(r: StatusResidual) -> Self {
-        Status(r.0.into())
-    }
-}
-
-impl<T> FromResidual<StatusResidual> for Result<T, ()> {
-    fn from_residual(r: StatusResidual) -> Self {
-        Err(Status(r.0.into()).into())
-    }
-}
-
-impl FromResidual<core::result::Result<Infallible, Error>> for Status {
-    fn from_residual(r: core::result::Result<Infallible, Error>) -> Self {
-        match r {
-            Err(err) => err.status(),
-            Ok(infallible) => match infallible {},
-        }
-    }
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;