how much would Arc cost?

Author: cyrgani

compiler/rustc_expand/src/proc_macro_server.rs

@@ -1,5 +1,5 @@
 use std::ops::{Bound, Range};
-use std::rc::Rc;
+use std::sync::Arc;
 
 use ast::token::IdentIsRaw;
 use rustc_ast as ast;
@@ -365,7 +365,7 @@ impl<'a, 'b> Rustc<'a, 'b> {
     pub(crate) fn ts_pm_to_rustc(&mut self, ts: BridgeTokenStream) -> tokenstream::TokenStream {
         let mut t = tokenstream::TokenStream::new(vec![]);
 
-        for tree in Rc::into_inner(ts.trees).expect("just decoded this `Rc`") {
+        for tree in Arc::into_inner(ts.trees).expect("just decoded this `Arc`") {
             use rustc_ast::token::*;
 
             // The code below is conservative, using `token_alone`/`Spacing::Alone`

library/proc_macro/src/bridge/client.rs

@@ -2,7 +2,7 @@
 
 use std::cell::RefCell;
 use std::marker::PhantomData;
-use std::rc::Rc;
+use std::sync::Arc as Rc;
 use std::sync::atomic::AtomicU32;
 
 use super::*;

library/proc_macro/src/bridge/mod.rs

@@ -10,8 +10,7 @@
 
 use std::hash::Hash;
 use std::ops::{Bound, Range};
-use std::rc::Rc;
-use std::sync::Once;
+use std::sync::{Arc as Rc, Once};
 use std::{fmt, marker, panic, thread};
 
 use crate::{Delimiter, Level};

library/proc_macro/src/bridge/rpc.rs

@@ -3,7 +3,7 @@
 use std::any::Any;
 use std::io::Write;
 use std::num::NonZero;
-use std::rc::Rc;
+use std::sync::Arc as Rc;
 
 use super::buffer::Buffer;
 

library/proc_macro/src/lib.rs

@@ -47,8 +47,8 @@ use core::ops::BitOr;
 use std::ffi::CStr;
 use std::ops::{Range, RangeBounds};
 use std::path::PathBuf;
-use std::rc::Rc;
 use std::str::FromStr;
+use std::sync::Arc as Rc;
 use std::{error, fmt};
 
 #[unstable(feature = "proc_macro_diagnostic", issue = "54140")]
@@ -378,7 +378,7 @@ extend_items!(Group Literal Punct Ident);
 /// Public implementation details for the `TokenStream` type, such as iterators.
 #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
 pub mod token_stream {
-    use std::rc::Rc;
+    use std::sync::Arc as Rc;
 
     use crate::{Group, Ident, Literal, Punct, TokenStream, TokenTree, bridge};