Parallel rustc needs synchronizing smart pointer cloning

src/librustc/hir/lowering.rs

@@ -44,6 +44,7 @@ use crate::middle::cstore::CrateStore;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_data_structures::indexed_vec::IndexVec;
 use rustc_data_structures::thin_vec::ThinVec;
+use rustc_data_structures::sync::Lrc;
 use crate::session::Session;
 use crate::session::config::nightly_options;
 use crate::util::common::FN_OUTPUT_NAME;
@@ -52,7 +53,6 @@ use crate::util::nodemap::{DefIdMap, NodeMap};
 use std::collections::{BTreeSet, BTreeMap};
 use std::fmt::Debug;
 use std::mem;
-use std::rc::Rc;
 use smallvec::SmallVec;
 use syntax::attr;
 use syntax::ast;
@@ -688,7 +688,7 @@ impl<'a> LoweringContext<'a> {
         &self,
         reason: CompilerDesugaringKind,
         span: Span,
-        allow_internal_unstable: Option<Rc<[Symbol]>>,
+        allow_internal_unstable: Option<Lrc<[Symbol]>>,
     ) -> Span {
         let mark = Mark::fresh(Mark::root());
         mark.set_expn_info(source_map::ExpnInfo {

src/libsyntax/ext/base.rs

@@ -622,7 +622,7 @@ pub enum SyntaxExtension {
     ProcMacro {
         expander: Box<dyn ProcMacro + sync::Sync + sync::Send>,
         /// Whitelist of unstable features that are treated as stable inside this macro
-        allow_internal_unstable: Option<Rc<[Symbol]>>,
+        allow_internal_unstable: Option<Lrc<[Symbol]>>,
         edition: Edition,
     },
 
@@ -642,7 +642,7 @@ pub enum SyntaxExtension {
         /// directly use `#[unstable]` things.
         ///
         /// Only allows things that require a feature gate in the given whitelist
-        allow_internal_unstable: Option<Rc<[Symbol]>>,
+        allow_internal_unstable: Option<Lrc<[Symbol]>>,
         /// Whether the contents of the macro can use `unsafe`
         /// without triggering the `unsafe_code` lint.
         allow_internal_unsafe: bool,
@@ -660,7 +660,7 @@ pub enum SyntaxExtension {
     IdentTT {
         expander: Box<dyn IdentMacroExpander + sync::Sync + sync::Send>,
         span: Option<Span>,
-        allow_internal_unstable: Option<Rc<[Symbol]>>,
+        allow_internal_unstable: Option<Lrc<[Symbol]>>,
     },
 
     /// An attribute-like procedural macro. TokenStream -> TokenStream.

src/libsyntax_pos/hygiene.rs

@@ -12,8 +12,8 @@ use crate::symbol::{keywords, Symbol};
 
 use serialize::{Encodable, Decodable, Encoder, Decoder};
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_data_structures::sync::Lrc;
 use std::{fmt, mem};
-use std::rc::Rc;
 
 /// A SyntaxContext represents a chain of macro expansions (represented by marks).
 #[derive(Clone, Copy, PartialEq, Eq, Default, PartialOrd, Ord, Hash)]
@@ -554,7 +554,7 @@ pub struct ExpnInfo {
     /// List of #[unstable]/feature-gated features that the macro is allowed to use
     /// internally without forcing the whole crate to opt-in
     /// to them.
-    pub allow_internal_unstable: Option<Rc<[Symbol]>>,
+    pub allow_internal_unstable: Option<Lrc<[Symbol]>>,
     /// Whether the macro is allowed to use `unsafe` internally
     /// even if the user crate has `#![forbid(unsafe_code)]`.
     pub allow_internal_unsafe: bool,