Rollup merge of #150166 - Urgau:const-item-lint-150157, r=Kivooeo

Don't lint on interior mutable `const` item coming from derefs

This PR fixes the `const_item_interior_mutations` lint so we don't lint on interior mutable `const` item coming from derefs.

Fixes https://github.com/rust-lang/rust/issues/150157

compiler/rustc_lint/src/interior_mutable_consts.rs

@@ -1,6 +1,7 @@
 use rustc_hir::attrs::AttributeKind;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::{Expr, ExprKind, ItemKind, Node, find_attr};
+use rustc_middle::ty::adjustment::Adjust;
 use rustc_session::{declare_lint, declare_lint_pass};
 
 use crate::lints::{ConstItemInteriorMutationsDiag, ConstItemInteriorMutationsSuggestionStatic};
@@ -77,6 +78,13 @@ impl<'tcx> LateLintPass<'tcx> for InteriorMutableConsts {
         if let ExprKind::Path(qpath) = &receiver.kind
             && let Res::Def(DefKind::Const | DefKind::AssocConst, const_did) =
                 typeck.qpath_res(qpath, receiver.hir_id)
+            // Don't consider derefs as those can do arbitrary things
+            // like using thread local (see rust-lang/rust#150157)
+            && !cx
+                .typeck_results()
+                .expr_adjustments(receiver)
+                .into_iter()
+                .any(|adj| matches!(adj.kind, Adjust::Deref(_)))
             // Let's do the attribute check after the other checks for perf reasons
             && find_attr!(
                 cx.tcx.get_all_attrs(method_did),

tests/ui/lint/const-item-interior-mutations-const-deref.rs

@@ -0,0 +1,28 @@
+// Regression test for <https://github.com/rust-lang/rust/issues/150157>
+//
+// We shouldn't lint on user types, including through deref.
+
+//@ check-pass
+
+use std::cell::Cell;
+use std::ops::Deref;
+
+// Cut down version of the issue reproducer without the thread local to just a Deref
+pub struct LocalKey<T> {
+    inner: T,
+}
+
+impl<T> Deref for LocalKey<T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        &self.inner
+    }
+}
+
+const LOCAL_COUNT: LocalKey<Cell<usize>> = LocalKey { inner: Cell::new(8) };
+
+fn main() {
+    let count = LOCAL_COUNT.get();
+    LOCAL_COUNT.set(count);
+}