repr_transparent_external_private_fields: special-case some std types

Author: GrigorenkoPV

compiler/rustc_hir_analysis/src/check/check.rs

@@ -5,7 +5,7 @@ use rustc_data_structures::unord::{UnordMap, UnordSet};
 use rustc_errors::codes::*;
 use rustc_errors::MultiSpan;
 use rustc_hir::def::{CtorKind, DefKind};
-use rustc_hir::Node;
+use rustc_hir::{LangItem, Node};
 use rustc_infer::infer::{RegionVariableOrigin, TyCtxtInferExt};
 use rustc_infer::traits::Obligation;
 use rustc_lint_defs::builtin::REPR_TRANSPARENT_EXTERNAL_PRIVATE_FIELDS;
@@ -1259,6 +1259,17 @@ pub(super) fn check_transparent<'tcx>(tcx: TyCtxt<'tcx>, adt: ty::AdtDef<'tcx>)
                 ty::Tuple(list) => list.iter().try_for_each(|t| check_non_exhaustive(tcx, t)),
                 ty::Array(ty, _) => check_non_exhaustive(tcx, *ty),
                 ty::Adt(def, args) => {
+                    if matches!(
+                        tcx.as_lang_item(def.did()),
+                        Some(LangItem::UnsafeCell | LangItem::ManuallyDrop | LangItem::MaybeUninit)
+                    ) || matches!(
+                        tcx.get_diagnostic_name(def.did()),
+                        Some(sym::Cell | sym::SyncUnsafeCell)
+                    ) {
+                        // These are the types from `std` that guarantee that
+                        // they have the same layout as `T`.
+                        return check_non_exhaustive(tcx, args.type_at(0));
+                    }
                     if !def.did().is_local() {
                         let non_exhaustive = def.is_variant_list_non_exhaustive()
                             || def

tests/ui/repr/repr-transparent-non-exhaustive-std.rs

@@ -0,0 +1,21 @@
+//@ check-pass
+
+#![feature(sync_unsafe_cell)]
+#![deny(repr_transparent_external_private_fields)]
+
+struct ZST;
+
+#[repr(transparent)]
+struct TransparentWithManuallyDropZST {
+    value: i32,
+    md: std::mem::ManuallyDrop<ZST>,
+    mu: std::mem::MaybeUninit<ZST>,
+    pd: std::marker::PhantomData<ZST>,
+    pp: std::marker::PhantomPinned,
+    c: std::cell::Cell<ZST>,
+    uc: std::cell::UnsafeCell<ZST>,
+    suc: std::cell::SyncUnsafeCell<ZST>,
+    zst: ZST,
+}
+
+fn main() {}