Rollup merge of #85724 - sexxi-goose:rox-fix-issue-85435, r=nikomatsakis

Fix issue 85435 by restricting Fake Read precision

This PR fixes the root bug of issue #85435 by restricting Fake Read precision in closures and removing the feature gate introduced in PR #85564. More info [here](#85561 (comment)) and [here](#85561 (comment)).

Closes #85561

r? ``@nikomatsakis``

Author: JohnTitor

compiler/rustc_mir_build/src/build/expr/as_rvalue.rs

@@ -186,25 +186,21 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 // };
                 // ```
                 //
-                // FIXME(RFC2229, rust#85435): Remove feature gate once diagnostics are
-                // improved and unsafe checking works properly in closure bodies again.
-                if this.tcx.features().capture_disjoint_fields {
-                    for (thir_place, cause, hir_id) in fake_reads.into_iter() {
-                        let place_builder =
-                            unpack!(block = this.as_place_builder(block, &this.thir[*thir_place]));
-
-                        if let Ok(place_builder_resolved) =
-                            place_builder.try_upvars_resolved(this.tcx, this.typeck_results)
-                        {
-                            let mir_place =
-                                place_builder_resolved.into_place(this.tcx, this.typeck_results);
-                            this.cfg.push_fake_read(
-                                block,
-                                this.source_info(this.tcx.hir().span(*hir_id)),
-                                *cause,
-                                mir_place,
-                            );
-                        }
+                for (thir_place, cause, hir_id) in fake_reads.into_iter() {
+                    let place_builder =
+                        unpack!(block = this.as_place_builder(block, &this.thir[*thir_place]));
+
+                    if let Ok(place_builder_resolved) =
+                        place_builder.try_upvars_resolved(this.tcx, this.typeck_results)
+                    {
+                        let mir_place =
+                            place_builder_resolved.into_place(this.tcx, this.typeck_results);
+                        this.cfg.push_fake_read(
+                            block,
+                            this.source_info(this.tcx.hir().span(*hir_id)),
+                            *cause,
+                            mir_place,
+                        );
                     }
                 }
 

compiler/rustc_typeck/src/check/upvar.rs

@@ -1588,6 +1588,11 @@ impl<'a, 'tcx> InferBorrowKind<'a, 'tcx> {
 impl<'a, 'tcx> euv::Delegate<'tcx> for InferBorrowKind<'a, 'tcx> {
     fn fake_read(&mut self, place: Place<'tcx>, cause: FakeReadCause, diag_expr_id: hir::HirId) {
         if let PlaceBase::Upvar(_) = place.base {
+            // We need to restrict Fake Read precision to avoid fake reading unsafe code,
+            // such as deref of a raw pointer.
+            let place = restrict_capture_precision(place);
+            let place =
+                restrict_repr_packed_field_ref_capture(self.fcx.tcx, self.fcx.param_env, &place);
             self.fake_reads.push((place, cause, diag_expr_id));
         }
     }