constify a couple thread_local statics

compiler/rustc_data_structures/src/sync/worker_local.rs

@@ -42,7 +42,7 @@ pub struct Registry(Arc<RegistryData>);
 thread_local! {
     /// The registry associated with the thread.
     /// This allows the `WorkerLocal` type to clone the registry in its constructor.
-    static REGISTRY: OnceCell<Registry> = OnceCell::new();
+    static REGISTRY: OnceCell<Registry> = const { OnceCell::new() };
 }
 
 struct ThreadData {

compiler/rustc_errors/src/markdown/term.rs

@@ -9,9 +9,9 @@ const DEFAULT_COLUMN_WIDTH: usize = 140;
 
 thread_local! {
     /// Track the position of viewable characters in our buffer
-    static CURSOR: Cell<usize> = Cell::new(0);
+    static CURSOR: Cell<usize> = const { Cell::new(0) };
     /// Width of the terminal
-    static WIDTH: Cell<usize> = Cell::new(DEFAULT_COLUMN_WIDTH);
+    static WIDTH: Cell<usize> = const { Cell::new(DEFAULT_COLUMN_WIDTH) };
 }
 
 /// Print to terminal output to a buffer

library/proc_macro/src/bridge/client.rs

@@ -284,7 +284,7 @@ impl<'a> scoped_cell::ApplyL<'a> for BridgeStateL {
 
 thread_local! {
     static BRIDGE_STATE: scoped_cell::ScopedCell<BridgeStateL> =
-        scoped_cell::ScopedCell::new(BridgeState::NotConnected);
+        const { scoped_cell::ScopedCell::new(BridgeState::NotConnected) };
 }
 
 impl BridgeState<'_> {

library/proc_macro/src/bridge/server.rs

@@ -152,7 +152,7 @@ thread_local! {
     /// This is required as the thread-local state in the proc_macro client does
     /// not handle being re-entered, and will invalidate all `Symbol`s when
     /// entering a nested macro.
-    static ALREADY_RUNNING_SAME_THREAD: Cell<bool> = Cell::new(false);
+    static ALREADY_RUNNING_SAME_THREAD: Cell<bool> = const { Cell::new(false) };
 }
 
 /// Keep `ALREADY_RUNNING_SAME_THREAD` (see also its documentation)