Auto merge of #115082 - Zoxc:syntax-context-decode-race, r=cjgillot

Fix races conditions with `SyntaxContext` decoding

This changes `SyntaxContext` decoding to work with concurrent decoding. The `remapped_ctxts` field now only stores `SyntaxContext` which have completed decoding, while the new `decoding` and `local_in_progress` keeps track of `SyntaxContext`s which are in process of being decoding and on which threads.

This fixes 2 issues with the current implementation. It can return an `SyntaxContext` which contains dummy data if another thread starts decoding before the first one has completely finished. Multiple threads could also allocate multiple `SyntaxContext`s for the same `raw_id`.

1 files changed, 6 insertions, 0 deletions

diff --git a/compiler/rustc_data_structures/src/sync/worker_local.rs b/compiler/rustc_data_structures/src/sync/worker_local.rs
index 8c84daf4f16..27d687c3cfe 100644
--- a/compiler/rustc_data_structures/src/sync/worker_local.rs
+++ b/compiler/rustc_data_structures/src/sync/worker_local.rs
@@ -171,3 +171,9 @@ impl<T> Deref for WorkerLocal<T> {
         unsafe { &self.locals.get_unchecked(self.registry.id().verify()).0 }
     }
 }
+
+impl<T: Default> Default for WorkerLocal<T> {
+    fn default() -> Self {
+        WorkerLocal::new(|_| T::default())
+    }
+}