Don't consider unstable fields always-inhabited

This reverts the hack in rust-lang#133889
now that `Pin`'s field is no longer public.

Author: Nadrieril

compiler/rustc_middle/src/ty/inhabitedness/mod.rs

@@ -43,7 +43,6 @@
 //! This code should only compile in modules where the uninhabitedness of `Foo`
 //! is visible.
 
-use rustc_span::sym;
 use rustc_type_ir::TyKind::*;
 use tracing::instrument;
 
@@ -85,21 +84,6 @@ impl<'tcx> VariantDef {
         InhabitedPredicate::all(
             tcx,
             self.fields.iter().map(|field| {
-                // Unstable fields are always considered to be inhabited. In the future,
-                // this could be extended to be conditional on the field being unstable
-                // only within the module that's querying the inhabitedness, like:
-                //     `let pred = pred.or(InhabitedPredicate::IsUnstable(field.did));`
-                // but this is unnecessary for now, since it would only affect nightly-only
-                // code or code within the standard library itself.
-                // HACK: We filter out `rustc_private` fields since with the flag
-                // `-Zforce-unstable-if-unmarked` we consider all unmarked fields to be
-                // unstable when building the compiler.
-                if tcx
-                    .lookup_stability(field.did)
-                    .is_some_and(|stab| stab.is_unstable() && stab.feature != sym::rustc_private)
-                {
-                    return InhabitedPredicate::True;
-                }
                 let pred = tcx.type_of(field.did).instantiate_identity().inhabited_predicate(tcx);
                 if adt.is_enum() {
                     return pred;

compiler/rustc_pattern_analysis/src/rustc.rs

@@ -15,7 +15,7 @@ use rustc_middle::ty::{
 };
 use rustc_middle::{bug, span_bug};
 use rustc_session::lint;
-use rustc_span::{DUMMY_SP, ErrorGuaranteed, Span, sym};
+use rustc_span::{DUMMY_SP, ErrorGuaranteed, Span};
 
 use crate::constructor::Constructor::*;
 use crate::constructor::{
@@ -227,10 +227,7 @@ impl<'p, 'tcx: 'p> RustcPatCtxt<'p, 'tcx> {
                         let is_visible =
                             adt.is_enum() || field.vis.is_accessible_from(cx.module, cx.tcx);
                         let is_uninhabited = cx.is_uninhabited(*ty);
-                        let is_unstable = cx.tcx.lookup_stability(field.did).is_some_and(|stab| {
-                            stab.is_unstable() && stab.feature != sym::rustc_private
-                        });
-                        let skip = is_uninhabited && (!is_visible || is_unstable);
+                        let skip = is_uninhabited && !is_visible;
                         (ty, PrivateUninhabitedField(skip))
                     });
                     cx.dropless_arena.alloc_from_iter(tys)