diff --git a/compiler/rustc_feature/src/accepted.rs b/compiler/rustc_feature/src/accepted.rs
index 0c5fe6e8d8b..d3c373d52f7 100644
--- a/compiler/rustc_feature/src/accepted.rs
+++ b/compiler/rustc_feature/src/accepted.rs
@@ -353,6 +353,9 @@ macro_rules! 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, "1.80.0", 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).
diff --git a/compiler/rustc_feature/src/unstable.rs b/compiler/rustc_feature/src/unstable.rs
index 1067156958d..fc3696c4022 100644
--- a/compiler/rustc_feature/src/unstable.rs
+++ b/compiler/rustc_feature/src/unstable.rs
@@ -580,9 +580,6 @@ pub fn internal(&self, feature: Symbol) -> bool {
     (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"`.
diff --git a/compiler/rustc_lint/src/types.rs b/compiler/rustc_lint/src/types.rs
index db4413149a4..c79da86ccc5 100644
--- a/compiler/rustc_lint/src/types.rs
+++ b/compiler/rustc_lint/src/types.rs
@@ -741,10 +741,6 @@ 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 {
-                        return None;
-                    }
-
                     let ty1 = field1.ty(tcx, args);
                     let ty2 = field2.ty(tcx, args);
 
diff --git a/tests/ui/feature-gates/feature-gate-result_ffi_guarantees.stderr b/tests/ui/feature-gates/feature-gate-result_ffi_guarantees.stderr
deleted file mode 100644
index 94416eb99c8..00000000000
--- a/tests/ui/feature-gates/feature-gate-result_ffi_guarantees.stderr
+++ /dev/null
@@ -1,349 +0,0 @@
-error: `extern` block uses type `Result<&u8, ()>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:20:24
-   |
-LL |     fn result_ref_t(x: Result<&'static u8, ()>);
-   |                        ^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-note: the lint level is defined here
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:2:9
-   |
-LL | #![deny(improper_ctypes)]
-   |         ^^^^^^^^^^^^^^^
-
-error: `extern` block uses type `Result<extern "C" fn(), ()>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:22:23
-   |
-LL |     fn result_fn_t(x: Result<extern "C" fn(), ()>);
-   |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<NonNull<u8>, ()>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:24:28
-   |
-LL |     fn result_nonnull_t(x: Result<std::ptr::NonNull<u8>, ()>);
-   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<Unique<u8>, ()>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:26:27
-   |
-LL |     fn result_unique_t(x: Result<std::ptr::Unique<u8>, ()>);
-   |                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<NonZero<u8>, ()>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:28:31
-   |
-LL |     fn result_nonzero_u8_t(x: Result<num::NonZero<u8>, ()>);
-   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<NonZero<u16>, ()>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:30:32
-   |
-LL |     fn result_nonzero_u16_t(x: Result<num::NonZero<u16>, ()>);
-   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<NonZero<u32>, ()>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:32:32
-   |
-LL |     fn result_nonzero_u32_t(x: Result<num::NonZero<u32>, ()>);
-   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<NonZero<u64>, ()>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:34:32
-   |
-LL |     fn result_nonzero_u64_t(x: Result<num::NonZero<u64>, ()>);
-   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<NonZero<usize>, ()>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:36:34
-   |
-LL |     fn result_nonzero_usize_t(x: Result<num::NonZero<usize>, ()>);
-   |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<NonZero<i8>, ()>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:38:31
-   |
-LL |     fn result_nonzero_i8_t(x: Result<num::NonZero<i8>, ()>);
-   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<NonZero<i16>, ()>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:40:32
-   |
-LL |     fn result_nonzero_i16_t(x: Result<num::NonZero<i16>, ()>);
-   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<NonZero<i32>, ()>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:42:32
-   |
-LL |     fn result_nonzero_i32_t(x: Result<num::NonZero<i32>, ()>);
-   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<NonZero<i64>, ()>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:44:32
-   |
-LL |     fn result_nonzero_i64_t(x: Result<num::NonZero<i64>, ()>);
-   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<NonZero<isize>, ()>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:46:34
-   |
-LL |     fn result_nonzero_isize_t(x: Result<num::NonZero<isize>, ()>);
-   |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<TransparentStruct<NonZero<u8>>, ()>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:48:39
-   |
-LL |     fn result_transparent_struct_t(x: Result<TransparentStruct<num::NonZero<u8>>, ()>);
-   |                                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<TransparentEnum<NonZero<u8>>, ()>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:50:37
-   |
-LL |     fn result_transparent_enum_t(x: Result<TransparentEnum<num::NonZero<u8>>, ()>);
-   |                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<NonZero<u8>, PhantomData<()>>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:52:28
-   |
-LL |     fn result_phantom_t(x: Result<num::NonZero<u8>, std::marker::PhantomData<()>>);
-   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<NonZero<u8>, Z>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:54:47
-   |
-LL |     fn result_1zst_exhaustive_no_variant_t(x: Result<num::NonZero<u8>, Z>);
-   |                                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<NonZero<u8>, NoField>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:56:45
-   |
-LL |     fn result_1zst_exhaustive_no_field_t(x: Result<num::NonZero<u8>, NoField>);
-   |                                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<(), &u8>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:59:24
-   |
-LL |     fn result_ref_e(x: Result<(), &'static u8>);
-   |                        ^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<(), extern "C" fn()>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:61:23
-   |
-LL |     fn result_fn_e(x: Result<(), extern "C" fn()>);
-   |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<(), NonNull<u8>>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:63:28
-   |
-LL |     fn result_nonnull_e(x: Result<(), std::ptr::NonNull<u8>>);
-   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<(), Unique<u8>>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:65:27
-   |
-LL |     fn result_unique_e(x: Result<(), std::ptr::Unique<u8>>);
-   |                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<(), NonZero<u8>>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:67:31
-   |
-LL |     fn result_nonzero_u8_e(x: Result<(), num::NonZero<u8>>);
-   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<(), NonZero<u16>>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:69:32
-   |
-LL |     fn result_nonzero_u16_e(x: Result<(), num::NonZero<u16>>);
-   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<(), NonZero<u32>>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:71:32
-   |
-LL |     fn result_nonzero_u32_e(x: Result<(), num::NonZero<u32>>);
-   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<(), NonZero<u64>>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:73:32
-   |
-LL |     fn result_nonzero_u64_e(x: Result<(), num::NonZero<u64>>);
-   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<(), NonZero<usize>>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:75:34
-   |
-LL |     fn result_nonzero_usize_e(x: Result<(), num::NonZero<usize>>);
-   |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<(), NonZero<i8>>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:77:31
-   |
-LL |     fn result_nonzero_i8_e(x: Result<(), num::NonZero<i8>>);
-   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<(), NonZero<i16>>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:79:32
-   |
-LL |     fn result_nonzero_i16_e(x: Result<(), num::NonZero<i16>>);
-   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<(), NonZero<i32>>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:81:32
-   |
-LL |     fn result_nonzero_i32_e(x: Result<(), num::NonZero<i32>>);
-   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<(), NonZero<i64>>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:83:32
-   |
-LL |     fn result_nonzero_i64_e(x: Result<(), num::NonZero<i64>>);
-   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<(), NonZero<isize>>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:85:34
-   |
-LL |     fn result_nonzero_isize_e(x: Result<(), num::NonZero<isize>>);
-   |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<(), TransparentStruct<NonZero<u8>>>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:87:39
-   |
-LL |     fn result_transparent_struct_e(x: Result<(), TransparentStruct<num::NonZero<u8>>>);
-   |                                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<(), TransparentEnum<NonZero<u8>>>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:89:37
-   |
-LL |     fn result_transparent_enum_e(x: Result<(), TransparentEnum<num::NonZero<u8>>>);
-   |                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<NonZero<u8>, PhantomData<()>>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:91:28
-   |
-LL |     fn result_phantom_e(x: Result<num::NonZero<u8>, std::marker::PhantomData<()>>);
-   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<Z, NonZero<u8>>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:93:47
-   |
-LL |     fn result_1zst_exhaustive_no_variant_e(x: Result<Z, num::NonZero<u8>>);
-   |                                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: `extern` block uses type `Result<NoField, NonZero<u8>>`, which is not FFI-safe
-  --> $DIR/feature-gate-result_ffi_guarantees.rs:95:45
-   |
-LL |     fn result_1zst_exhaustive_no_field_e(x: Result<NoField, num::NonZero<u8>>);
-   |                                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
-   |
-   = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
-   = note: enum has no representation hint
-
-error: aborting due to 38 previous errors
-
diff --git a/tests/ui/lint/lint-ctypes-enum.rs b/tests/ui/lint/lint-ctypes-enum.rs
index cb8e9e80675..19af1de9576 100644
--- a/tests/ui/lint/lint-ctypes-enum.rs
+++ b/tests/ui/lint/lint-ctypes-enum.rs
@@ -2,7 +2,6 @@
 #![deny(improper_ctypes)]
 #![feature(ptr_internals)]
 #![feature(transparent_unions)]
-#![feature(result_ffi_guarantees)]
 
 use std::num;
 
diff --git a/tests/ui/lint/lint-ctypes-enum.stderr b/tests/ui/lint/lint-ctypes-enum.stderr
index bba5b09b69c..8e92e7e6946 100644
--- a/tests/ui/lint/lint-ctypes-enum.stderr
+++ b/tests/ui/lint/lint-ctypes-enum.stderr
@@ -1,5 +1,5 @@
 error: `extern` block uses type `U`, which is not FFI-safe
-  --> $DIR/lint-ctypes-enum.rs:69:14
+  --> $DIR/lint-ctypes-enum.rs:68:14
    |
 LL |     fn uf(x: U);
    |              ^ not FFI-safe
@@ -7,7 +7,7 @@ LL |     fn uf(x: U);
    = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
    = note: enum has no representation hint
 note: the type is defined here
-  --> $DIR/lint-ctypes-enum.rs:10:1
+  --> $DIR/lint-ctypes-enum.rs:9:1
    |
 LL | enum U {
    | ^^^^^^
@@ -18,7 +18,7 @@ LL | #![deny(improper_ctypes)]
    |         ^^^^^^^^^^^^^^^
 
 error: `extern` block uses type `B`, which is not FFI-safe
-  --> $DIR/lint-ctypes-enum.rs:70:14
+  --> $DIR/lint-ctypes-enum.rs:69:14
    |
 LL |     fn bf(x: B);
    |              ^ not FFI-safe
@@ -26,13 +26,13 @@ LL |     fn bf(x: B);
    = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
    = note: enum has no representation hint
 note: the type is defined here
-  --> $DIR/lint-ctypes-enum.rs:13:1
+  --> $DIR/lint-ctypes-enum.rs:12:1
    |
 LL | enum B {
    | ^^^^^^
 
 error: `extern` block uses type `T`, which is not FFI-safe
-  --> $DIR/lint-ctypes-enum.rs:71:14
+  --> $DIR/lint-ctypes-enum.rs:70:14
    |
 LL |     fn tf(x: T);
    |              ^ not FFI-safe
@@ -40,13 +40,13 @@ LL |     fn tf(x: T);
    = help: consider adding a `#[repr(C)]`, `#[repr(transparent)]`, or integer `#[repr(...)]` attribute to this enum
    = note: enum has no representation hint
 note: the type is defined here
-  --> $DIR/lint-ctypes-enum.rs:17:1
+  --> $DIR/lint-ctypes-enum.rs:16:1
    |
 LL | enum T {
    | ^^^^^^
 
 error: `extern` block uses type `u128`, which is not FFI-safe
-  --> $DIR/lint-ctypes-enum.rs:83:31
+  --> $DIR/lint-ctypes-enum.rs:82:31
    |
 LL |     fn option_nonzero_u128(x: Option<num::NonZero<u128>>);
    |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
@@ -54,7 +54,7 @@ LL |     fn option_nonzero_u128(x: Option<num::NonZero<u128>>);
    = note: 128-bit integers don't currently have a known stable ABI
 
 error: `extern` block uses type `i128`, which is not FFI-safe
-  --> $DIR/lint-ctypes-enum.rs:90:31
+  --> $DIR/lint-ctypes-enum.rs:89:31
    |
 LL |     fn option_nonzero_i128(x: Option<num::NonZero<i128>>);
    |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
@@ -62,7 +62,7 @@ LL |     fn option_nonzero_i128(x: Option<num::NonZero<i128>>);
    = note: 128-bit integers don't currently have a known stable ABI
 
 error: `extern` block uses type `Option<TransparentUnion<NonZero<u8>>>`, which is not FFI-safe
-  --> $DIR/lint-ctypes-enum.rs:95:36
+  --> $DIR/lint-ctypes-enum.rs:94:36
    |
 LL |     fn option_transparent_union(x: Option<TransparentUnion<num::NonZero<u8>>>);
    |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
@@ -71,7 +71,7 @@ LL |     fn option_transparent_union(x: Option<TransparentUnion<num::NonZero<u8>
    = note: enum has no representation hint
 
 error: `extern` block uses type `Option<Rust<NonZero<u8>>>`, which is not FFI-safe
-  --> $DIR/lint-ctypes-enum.rs:97:28
+  --> $DIR/lint-ctypes-enum.rs:96:28
    |
 LL |     fn option_repr_rust(x: Option<Rust<num::NonZero<u8>>>);
    |                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
@@ -80,7 +80,7 @@ LL |     fn option_repr_rust(x: Option<Rust<num::NonZero<u8>>>);
    = note: enum has no representation hint
 
 error: `extern` block uses type `u128`, which is not FFI-safe
-  --> $DIR/lint-ctypes-enum.rs:107:33
+  --> $DIR/lint-ctypes-enum.rs:106:33
    |
 LL |     fn result_nonzero_u128_t(x: Result<num::NonZero<u128>, ()>);
    |                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
@@ -88,7 +88,7 @@ LL |     fn result_nonzero_u128_t(x: Result<num::NonZero<u128>, ()>);
    = note: 128-bit integers don't currently have a known stable ABI
 
 error: `extern` block uses type `i128`, which is not FFI-safe
-  --> $DIR/lint-ctypes-enum.rs:114:33
+  --> $DIR/lint-ctypes-enum.rs:113:33
    |
 LL |     fn result_nonzero_i128_t(x: Result<num::NonZero<i128>, ()>);
    |                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
@@ -96,7 +96,7 @@ LL |     fn result_nonzero_i128_t(x: Result<num::NonZero<i128>, ()>);
    = note: 128-bit integers don't currently have a known stable ABI
 
 error: `extern` block uses type `Result<TransparentUnion<NonZero<u8>>, ()>`, which is not FFI-safe
-  --> $DIR/lint-ctypes-enum.rs:119:38
+  --> $DIR/lint-ctypes-enum.rs:118:38
    |
 LL |     fn result_transparent_union_t(x: Result<TransparentUnion<num::NonZero<u8>>, ()>);
    |                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
@@ -105,7 +105,7 @@ LL |     fn result_transparent_union_t(x: Result<TransparentUnion<num::NonZero<u
    = note: enum has no representation hint
 
 error: `extern` block uses type `Result<Rust<NonZero<u8>>, ()>`, which is not FFI-safe
-  --> $DIR/lint-ctypes-enum.rs:121:30
+  --> $DIR/lint-ctypes-enum.rs:120:30
    |
 LL |     fn result_repr_rust_t(x: Result<Rust<num::NonZero<u8>>, ()>);
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
@@ -114,7 +114,7 @@ LL |     fn result_repr_rust_t(x: Result<Rust<num::NonZero<u8>>, ()>);
    = note: enum has no representation hint
 
 error: `extern` block uses type `Result<NonZero<u8>, U>`, which is not FFI-safe
-  --> $DIR/lint-ctypes-enum.rs:125:51
+  --> $DIR/lint-ctypes-enum.rs:124:51
    |
 LL |     fn result_1zst_exhaustive_single_variant_t(x: Result<num::NonZero<u8>, U>);
    |                                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
@@ -123,7 +123,7 @@ LL |     fn result_1zst_exhaustive_single_variant_t(x: Result<num::NonZero<u8>,
    = note: enum has no representation hint
 
 error: `extern` block uses type `Result<NonZero<u8>, B>`, which is not FFI-safe
-  --> $DIR/lint-ctypes-enum.rs:127:53
+  --> $DIR/lint-ctypes-enum.rs:126:53
    |
 LL |     fn result_1zst_exhaustive_multiple_variant_t(x: Result<num::NonZero<u8>, B>);
    |                                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
@@ -132,7 +132,7 @@ LL |     fn result_1zst_exhaustive_multiple_variant_t(x: Result<num::NonZero<u8>
    = note: enum has no representation hint
 
 error: `extern` block uses type `Result<NonZero<u8>, NonExhaustive>`, which is not FFI-safe
-  --> $DIR/lint-ctypes-enum.rs:129:51
+  --> $DIR/lint-ctypes-enum.rs:128:51
    |
 LL |     fn result_1zst_non_exhaustive_no_variant_t(x: Result<num::NonZero<u8>, NonExhaustive>);
    |                                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
@@ -141,7 +141,7 @@ LL |     fn result_1zst_non_exhaustive_no_variant_t(x: Result<num::NonZero<u8>,
    = note: enum has no representation hint
 
 error: `extern` block uses type `Result<NonZero<u8>, Field>`, which is not FFI-safe
-  --> $DIR/lint-ctypes-enum.rs:132:49
+  --> $DIR/lint-ctypes-enum.rs:131:49
    |
 LL |     fn result_1zst_exhaustive_single_field_t(x: Result<num::NonZero<u8>, Field>);
    |                                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
@@ -150,7 +150,7 @@ LL |     fn result_1zst_exhaustive_single_field_t(x: Result<num::NonZero<u8>, Fi
    = note: enum has no representation hint
 
 error: `extern` block uses type `Result<Result<(), NonZero<u8>>, ()>`, which is not FFI-safe
-  --> $DIR/lint-ctypes-enum.rs:134:30
+  --> $DIR/lint-ctypes-enum.rs:133:30
    |
 LL |     fn result_cascading_t(x: Result<Result<(), num::NonZero<u8>>, ()>);
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
@@ -159,7 +159,7 @@ LL |     fn result_cascading_t(x: Result<Result<(), num::NonZero<u8>>, ()>);
    = note: enum has no representation hint
 
 error: `extern` block uses type `u128`, which is not FFI-safe
-  --> $DIR/lint-ctypes-enum.rs:145:33
+  --> $DIR/lint-ctypes-enum.rs:144:33
    |
 LL |     fn result_nonzero_u128_e(x: Result<(), num::NonZero<u128>>);
    |                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
@@ -167,7 +167,7 @@ LL |     fn result_nonzero_u128_e(x: Result<(), num::NonZero<u128>>);
    = note: 128-bit integers don't currently have a known stable ABI
 
 error: `extern` block uses type `i128`, which is not FFI-safe
-  --> $DIR/lint-ctypes-enum.rs:152:33
+  --> $DIR/lint-ctypes-enum.rs:151:33
    |
 LL |     fn result_nonzero_i128_e(x: Result<(), num::NonZero<i128>>);
    |                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
@@ -175,7 +175,7 @@ LL |     fn result_nonzero_i128_e(x: Result<(), num::NonZero<i128>>);
    = note: 128-bit integers don't currently have a known stable ABI
 
 error: `extern` block uses type `Result<(), TransparentUnion<NonZero<u8>>>`, which is not FFI-safe
-  --> $DIR/lint-ctypes-enum.rs:157:38
+  --> $DIR/lint-ctypes-enum.rs:156:38
    |
 LL |     fn result_transparent_union_e(x: Result<(), TransparentUnion<num::NonZero<u8>>>);
    |                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
@@ -184,7 +184,7 @@ LL |     fn result_transparent_union_e(x: Result<(), TransparentUnion<num::NonZe
    = note: enum has no representation hint
 
 error: `extern` block uses type `Result<(), Rust<NonZero<u8>>>`, which is not FFI-safe
-  --> $DIR/lint-ctypes-enum.rs:159:30
+  --> $DIR/lint-ctypes-enum.rs:158:30
    |
 LL |     fn result_repr_rust_e(x: Result<(), Rust<num::NonZero<u8>>>);
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
@@ -193,7 +193,7 @@ LL |     fn result_repr_rust_e(x: Result<(), Rust<num::NonZero<u8>>>);
    = note: enum has no representation hint
 
 error: `extern` block uses type `Result<U, NonZero<u8>>`, which is not FFI-safe
-  --> $DIR/lint-ctypes-enum.rs:163:51
+  --> $DIR/lint-ctypes-enum.rs:162:51
    |
 LL |     fn result_1zst_exhaustive_single_variant_e(x: Result<U, num::NonZero<u8>>);
    |                                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
@@ -202,7 +202,7 @@ LL |     fn result_1zst_exhaustive_single_variant_e(x: Result<U, num::NonZero<u8
    = note: enum has no representation hint
 
 error: `extern` block uses type `Result<B, NonZero<u8>>`, which is not FFI-safe
-  --> $DIR/lint-ctypes-enum.rs:165:53
+  --> $DIR/lint-ctypes-enum.rs:164:53
    |
 LL |     fn result_1zst_exhaustive_multiple_variant_e(x: Result<B, num::NonZero<u8>>);
    |                                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
@@ -211,7 +211,7 @@ LL |     fn result_1zst_exhaustive_multiple_variant_e(x: Result<B, num::NonZero<
    = note: enum has no representation hint
 
 error: `extern` block uses type `Result<NonExhaustive, NonZero<u8>>`, which is not FFI-safe
-  --> $DIR/lint-ctypes-enum.rs:167:51
+  --> $DIR/lint-ctypes-enum.rs:166:51
    |
 LL |     fn result_1zst_non_exhaustive_no_variant_e(x: Result<NonExhaustive, num::NonZero<u8>>);
    |                                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
@@ -220,7 +220,7 @@ LL |     fn result_1zst_non_exhaustive_no_variant_e(x: Result<NonExhaustive, num
    = note: enum has no representation hint
 
 error: `extern` block uses type `Result<Field, NonZero<u8>>`, which is not FFI-safe
-  --> $DIR/lint-ctypes-enum.rs:170:49
+  --> $DIR/lint-ctypes-enum.rs:169:49
    |
 LL |     fn result_1zst_exhaustive_single_field_e(x: Result<Field, num::NonZero<u8>>);
    |                                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
@@ -229,7 +229,7 @@ LL |     fn result_1zst_exhaustive_single_field_e(x: Result<Field, num::NonZero<
    = note: enum has no representation hint
 
 error: `extern` block uses type `Result<(), Result<(), NonZero<u8>>>`, which is not FFI-safe
-  --> $DIR/lint-ctypes-enum.rs:172:30
+  --> $DIR/lint-ctypes-enum.rs:171:30
    |
 LL |     fn result_cascading_e(x: Result<(), Result<(), num::NonZero<u8>>>);
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not FFI-safe
@@ -238,7 +238,7 @@ LL |     fn result_cascading_e(x: Result<(), Result<(), num::NonZero<u8>>>);
    = note: enum has no representation hint
 
 error: `extern` block uses type `Result<(), ()>`, which is not FFI-safe
-  --> $DIR/lint-ctypes-enum.rs:174:27
+  --> $DIR/lint-ctypes-enum.rs:173:27
    |
 LL |     fn result_unit_t_e(x: Result<(), ()>);
    |                           ^^^^^^^^^^^^^^ not FFI-safe
diff --git a/tests/ui/feature-gates/feature-gate-result_ffi_guarantees.rs b/tests/ui/rfcs/rfc-3391-result-ffi-guarantees.rs
similarity index 61%
rename from tests/ui/feature-gates/feature-gate-result_ffi_guarantees.rs
rename to tests/ui/rfcs/rfc-3391-result-ffi-guarantees.rs
index dda317aecc3..dea9f60c7e1 100644
--- a/tests/ui/feature-gates/feature-gate-result_ffi_guarantees.rs
+++ b/tests/ui/rfcs/rfc-3391-result-ffi-guarantees.rs
@@ -1,3 +1,4 @@
+//@ build-pass
 #![allow(dead_code)]
 #![deny(improper_ctypes)]
 #![feature(ptr_internals)]
@@ -18,82 +19,44 @@ enum TransparentEnum<T> {
 
 extern "C" {
     fn result_ref_t(x: Result<&'static u8, ()>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_fn_t(x: Result<extern "C" fn(), ()>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_nonnull_t(x: Result<std::ptr::NonNull<u8>, ()>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_unique_t(x: Result<std::ptr::Unique<u8>, ()>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_nonzero_u8_t(x: Result<num::NonZero<u8>, ()>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_nonzero_u16_t(x: Result<num::NonZero<u16>, ()>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_nonzero_u32_t(x: Result<num::NonZero<u32>, ()>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_nonzero_u64_t(x: Result<num::NonZero<u64>, ()>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_nonzero_usize_t(x: Result<num::NonZero<usize>, ()>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_nonzero_i8_t(x: Result<num::NonZero<i8>, ()>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_nonzero_i16_t(x: Result<num::NonZero<i16>, ()>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_nonzero_i32_t(x: Result<num::NonZero<i32>, ()>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_nonzero_i64_t(x: Result<num::NonZero<i64>, ()>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_nonzero_isize_t(x: Result<num::NonZero<isize>, ()>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_transparent_struct_t(x: Result<TransparentStruct<num::NonZero<u8>>, ()>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_transparent_enum_t(x: Result<TransparentEnum<num::NonZero<u8>>, ()>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_phantom_t(x: Result<num::NonZero<u8>, std::marker::PhantomData<()>>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_1zst_exhaustive_no_variant_t(x: Result<num::NonZero<u8>, Z>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_1zst_exhaustive_no_field_t(x: Result<num::NonZero<u8>, NoField>);
-    //~^ ERROR `extern` block uses type `Result
 
     fn result_ref_e(x: Result<(), &'static u8>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_fn_e(x: Result<(), extern "C" fn()>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_nonnull_e(x: Result<(), std::ptr::NonNull<u8>>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_unique_e(x: Result<(), std::ptr::Unique<u8>>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_nonzero_u8_e(x: Result<(), num::NonZero<u8>>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_nonzero_u16_e(x: Result<(), num::NonZero<u16>>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_nonzero_u32_e(x: Result<(), num::NonZero<u32>>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_nonzero_u64_e(x: Result<(), num::NonZero<u64>>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_nonzero_usize_e(x: Result<(), num::NonZero<usize>>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_nonzero_i8_e(x: Result<(), num::NonZero<i8>>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_nonzero_i16_e(x: Result<(), num::NonZero<i16>>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_nonzero_i32_e(x: Result<(), num::NonZero<i32>>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_nonzero_i64_e(x: Result<(), num::NonZero<i64>>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_nonzero_isize_e(x: Result<(), num::NonZero<isize>>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_transparent_struct_e(x: Result<(), TransparentStruct<num::NonZero<u8>>>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_transparent_enum_e(x: Result<(), TransparentEnum<num::NonZero<u8>>>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_phantom_e(x: Result<num::NonZero<u8>, std::marker::PhantomData<()>>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_1zst_exhaustive_no_variant_e(x: Result<Z, num::NonZero<u8>>);
-    //~^ ERROR `extern` block uses type `Result
     fn result_1zst_exhaustive_no_field_e(x: Result<NoField, num::NonZero<u8>>);
-    //~^ ERROR `extern` block uses type `Result
 }
 
 pub fn main() {}