Avoid shadowing user provided types or type aliases in thread_local!

By using qualified imports, i.e. `$crate::...::LocalKey`.
qinheping · Oct 18, 2024 · a6e300e · a6e300e
1 parent 4d2c969
commit a6e300e
Show file tree

Hide file tree

Showing 3 changed files with 49 additions and 22 deletions.
diff --git a/std/src/sys/thread_local/native/mod.rs b/std/src/sys/thread_local/native/mod.rs
@@ -49,20 +49,21 @@ pub use lazy::Storage as LazyStorage;
 #[unstable(feature = "thread_local_internals", issue = "none")]
 #[rustc_macro_transparency = "semitransparent"]
 pub macro thread_local_inner {
-    // used to generate the `LocalKey` value for const-initialized thread locals
+    // NOTE: we cannot import `LocalKey`, `LazyStorage` or `EagerStorage` with a `use` because that
+    // can shadow user provided type or type alias with a matching name. Please update the shadowing
+    // test in `tests/thread.rs` if these types are renamed.
+
+    // Used to generate the `LocalKey` value for const-initialized thread locals.
     (@key $t:ty, const $init:expr) => {{
         const __INIT: $t = $init;
 
         unsafe {
-            use $crate::mem::needs_drop;
-            use $crate::thread::LocalKey;
-            use $crate::thread::local_impl::EagerStorage;
-
-            LocalKey::new(const {
-                if needs_drop::<$t>() {
+            $crate::thread::LocalKey::new(const {
+                if $crate::mem::needs_drop::<$t>() {
                     |_| {
                         #[thread_local]
-                        static VAL: EagerStorage<$t> = EagerStorage::new(__INIT);
+                        static VAL: $crate::thread::local_impl::EagerStorage<$t>
+                            = $crate::thread::local_impl::EagerStorage::new(__INIT);
                         VAL.get()
                     }
                 } else {
@@ -84,21 +85,19 @@ pub macro thread_local_inner {
         }
 
         unsafe {
-            use $crate::mem::needs_drop;
-            use $crate::thread::LocalKey;
-            use $crate::thread::local_impl::LazyStorage;
-
-            LocalKey::new(const {
-                if needs_drop::<$t>() {
+            $crate::thread::LocalKey::new(const {
+                if $crate::mem::needs_drop::<$t>() {
                     |init| {
                         #[thread_local]
-                        static VAL: LazyStorage<$t, ()> = LazyStorage::new();
+                        static VAL: $crate::thread::local_impl::LazyStorage<$t, ()>
+                            = $crate::thread::local_impl::LazyStorage::new();
                         VAL.get_or_init(init, __init)
                     }
                 } else {
                     |init| {
                         #[thread_local]
-                        static VAL: LazyStorage<$t, !> = LazyStorage::new();
+                        static VAL: $crate::thread::local_impl::LazyStorage<$t, !>
+                            = $crate::thread::local_impl::LazyStorage::new();
                         VAL.get_or_init(init, __init)
                     }
                 }

diff --git a/std/src/sys/thread_local/os.rs b/std/src/sys/thread_local/os.rs
@@ -15,19 +15,24 @@ pub macro thread_local_inner {
         $crate::thread::local_impl::thread_local_inner!(@key $t, { const INIT_EXPR: $t = $init; INIT_EXPR })
     },
 
-    // used to generate the `LocalKey` value for `thread_local!`
+    // NOTE: we cannot import `Storage` or `LocalKey` with a `use` because that can shadow user
+    // provided type or type alias with a matching name. Please update the shadowing test in
+    // `tests/thread.rs` if these types are renamed.
+
+    // used to generate the `LocalKey` value for `thread_local!`.
     (@key $t:ty, $init:expr) => {{
         #[inline]
         fn __init() -> $t { $init }
 
+        // NOTE: this cannot import `LocalKey` or `Storage` with a `use` because that can shadow
+        // user provided type or type alias with a matching name. Please update the shadowing test
+        // in `tests/thread.rs` if these types are renamed.
         unsafe {
-            use $crate::thread::LocalKey;
-            use $crate::thread::local_impl::Storage;
-
             // Inlining does not work on windows-gnu due to linking errors around
             // dllimports. See https://github.com/rust-lang/rust/issues/109797.
-            LocalKey::new(#[cfg_attr(windows, inline(never))] |init| {
-                static VAL: Storage<$t> = Storage::new();
+            $crate::thread::LocalKey::new(#[cfg_attr(windows, inline(never))] |init| {
+                static VAL: $crate::thread::local_impl::Storage<$t>
+                    = $crate::thread::local_impl::Storage::new();
                 VAL.get(init, __init)
             })
         }

diff --git a/std/tests/thread.rs b/std/tests/thread.rs
@@ -38,6 +38,29 @@ fn thread_local_containing_const_statements() {
     assert_eq!(REFCELL.take(), 1);
 }
 
+#[test]
+fn thread_local_hygeiene() {
+    // Previously `thread_local_inner!` had use imports for `LocalKey`, `Storage`, `EagerStorage`
+    // and `LazyStorage`. The use imports will shadow a user-provided type or type alias if the
+    // user-provided type or type alias has the same name. Make sure that this does not happen. See
+    // <https://github.com/rust-lang/rust/issues/131863>.
+    //
+    // NOTE: if the internal implementation details change (i.e. get renamed), this test should be
+    // updated.
+
+    #![allow(dead_code)]
+    type LocalKey = ();
+    type Storage = ();
+    type LazyStorage = ();
+    type EagerStorage = ();
+    thread_local! {
+        static A: LocalKey = const { () };
+        static B: Storage = const { () };
+        static C: LazyStorage = const { () };
+        static D: EagerStorage = const { () };
+    }
+}
+
 #[test]
 // Include an ignore list on purpose, so that new platforms don't miss it
 #[cfg_attr(