Auto merge of #130628 - workingjubilee:clean-up-result-ffi-guarantees, r=RalfJung

Finish stabilization of `result_ffi_guarantees`
The internal linting has been changed, so all that is left is making sure we stabilize what we want to stabilize.

Author: bors

compiler/rustc_feature/src/accepted.rs

@@ -353,6 +353,9 @@ declare_features! (
 (accepted, repr_packed,"1.33.0",Some(33158)),
 /// Allows `#[repr(transparent)]` attribute on newtype structs.
 (accepted, repr_transparent,"1.28.0",Some(43036)),
+/// Allows enums like Result<T, E> to be used across FFI, if T's niche value can
+/// be used to describe E or vice-versa.
+(accepted, result_ffi_guarantees,"CURRENT_RUSTC_VERSION",Some(110503)),
 /// Allows return-position `impl Trait` in traits.
 (accepted, return_position_impl_trait_in_trait,"1.75.0",Some(91611)),
 /// Allows code like `let x: &'static u32 = &42` to work (RFC 1414).

compiler/rustc_feature/src/unstable.rs

@@ -580,9 +580,6 @@ declare_features! (
 (incomplete, repr128,"1.16.0",Some(56071)),
 /// Allows `repr(simd)` and importing the various simd intrinsics.
 (unstable, repr_simd,"1.4.0",Some(27731)),
-/// Allows enums like Result<T, E> to be used across FFI, if T's niche value can
-/// be used to describe E or vise-versa.
-(unstable, result_ffi_guarantees,"1.80.0",Some(110503)),
 /// Allows bounding the return type of AFIT/RPITIT.
 (unstable, return_type_notation,"1.70.0",Some(109417)),
 /// Allows `extern "rust-cold"`.

compiler/rustc_lint/src/types.rs

@@ -730,7 +730,6 @@ fn is_niche_optimization_candidate<'tcx>(
 /// can, return the type that `ty` can be safely converted to, otherwise return `None`.
 /// Currently restricted to function pointers, boxes, references, `core::num::NonZero`,
 /// `core::ptr::NonNull`, and `#[repr(transparent)]` newtypes.
-/// FIXME: This duplicates code in codegen.
 pub(crate)fnrepr_nullable_ptr<'tcx>(
 tcx:TyCtxt<'tcx>,
 param_env: ty::ParamEnv<'tcx>,
@@ -743,10 +742,6 @@ pub(crate) fn repr_nullable_ptr<'tcx>(
 [var_one, var_two] => match(&var_one.fields.raw[..],&var_two.fields.raw[..]){
 ([],[field]) | ([field],[]) => field.ty(tcx, args),
 ([field1],[field2]) => {
-if !tcx.features().result_ffi_guarantees{
-returnNone;
-}
-
 let ty1 = field1.ty(tcx, args);
 let ty2 = field2.ty(tcx, args);