Add AllowInternalUnstable enum to avoid Arc clones for static desugaring feature lists

compiler/rustc_ast_lowering/src/contract.rs

@@ -1,4 +1,4 @@
-use std::sync::Arc;
+use std::borrow::Cow;
 
 use rustc_hir::attrs::lang_items::LangItem;
 use thin_vec::thin_vec;
@@ -143,7 +143,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         let req_span = self.mark_span_with_reason(
             rustc_span::DesugaringKind::Contract,
             lowered_req.span,
-            Some(Arc::clone(&crate::ALLOW_CONTRACTS)),
+            Some(Cow::Borrowed(crate::ALLOW_CONTRACTS)),
         );
         let precond = self.expr_call_lang_item_fn_mut(
             req_span,
@@ -161,7 +161,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         let ens_span = self.mark_span_with_reason(
             rustc_span::DesugaringKind::Contract,
             ens_span,
-            Some(Arc::clone(&crate::ALLOW_CONTRACTS)),
+            Some(Cow::Borrowed(crate::ALLOW_CONTRACTS)),
         );
         let lowered_ens = self.lower_expr_mut(&ens);
         self.expr_call_lang_item_fn(

compiler/rustc_ast_lowering/src/expr.rs

@@ -1,6 +1,6 @@
+use std::borrow::Cow;
 use std::mem;
 use std::ops::ControlFlow;
-use std::sync::Arc;
 
 use rustc_ast::node_id::NodeMap;
 use rustc_ast::visit::{Visitor, walk_expr};
@@ -742,15 +742,15 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     this.mark_span_with_reason(
                         DesugaringKind::TryBlock,
                         expr.span,
-                        Some(Arc::clone(&crate::ALLOW_TRY_TRAIT)),
+                        Some(Cow::Borrowed(crate::ALLOW_TRY_TRAIT)),
                     ),
                     expr,
                 )
             } else {
                 let try_span = this.mark_span_with_reason(
                     DesugaringKind::TryBlock,
                     this.tcx.sess.source_map().end_point(body.span),
-                    Some(Arc::clone(&crate::ALLOW_TRY_TRAIT)),
+                    Some(Cow::Borrowed(crate::ALLOW_TRY_TRAIT)),
                 );
 
                 (try_span, this.expr_unit(try_span))
@@ -878,7 +878,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 let unstable_span = self.mark_span_with_reason(
                     DesugaringKind::Async,
                     self.lower_span(span),
-                    Some(Arc::clone(self.allow_gen_future())),
+                    Some(self.allow_gen_future()),
                 );
                 let resume_ty = self.make_lang_item_qpath(LangItem::ResumeTy, unstable_span, None);
                 let input_ty = hir::Ty {
@@ -1037,15 +1037,15 @@ impl<'hir> LoweringContext<'_, 'hir> {
         };
 
         let features = match await_kind {
-            FutureKind::Future if is_async_gen => Some(Arc::clone(&crate::ALLOW_ASYNC_GEN)),
+            FutureKind::Future if is_async_gen => Some(Cow::Borrowed(crate::ALLOW_ASYNC_GEN)),
             FutureKind::Future => None,
-            FutureKind::AsyncIterator => Some(Arc::clone(&crate::ALLOW_FOR_AWAIT)),
+            FutureKind::AsyncIterator => Some(Cow::Borrowed(crate::ALLOW_FOR_AWAIT)),
         };
         let span = self.mark_span_with_reason(DesugaringKind::Await, await_kw_span, features);
         let gen_future_span = self.mark_span_with_reason(
             DesugaringKind::Await,
             full_span,
-            Some(Arc::clone(self.allow_gen_future())),
+            Some(self.allow_gen_future()),
         );
         let expr_hir_id = expr.hir_id;
 
@@ -1727,7 +1727,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
             let desugar_span = self.mark_span_with_reason(
                 DesugaringKind::Async,
                 span,
-                Some(Arc::clone(&crate::ALLOW_ASYNC_GEN)),
+                Some(Cow::Borrowed(crate::ALLOW_ASYNC_GEN)),
             );
             let wrapped_yielded = self.expr_call_lang_item_fn(
                 desugar_span,
@@ -1946,13 +1946,13 @@ impl<'hir> LoweringContext<'_, 'hir> {
         let unstable_span = self.mark_span_with_reason(
             DesugaringKind::QuestionMark,
             span,
-            Some(Arc::clone(&crate::ALLOW_TRY_TRAIT)),
+            Some(Cow::Borrowed(crate::ALLOW_TRY_TRAIT)),
         );
         let try_span = self.tcx.sess.source_map().end_point(span);
         let try_span = self.mark_span_with_reason(
             DesugaringKind::QuestionMark,
             try_span,
-            Some(Arc::clone(&crate::ALLOW_TRY_TRAIT)),
+            Some(Cow::Borrowed(crate::ALLOW_TRY_TRAIT)),
         );
 
         // `Try::branch(<expr>)`
@@ -2049,7 +2049,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         let unstable_span = self.mark_span_with_reason(
             DesugaringKind::YeetExpr,
             span,
-            Some(Arc::clone(&crate::ALLOW_TRY_TRAIT)),
+            Some(Cow::Borrowed(crate::ALLOW_TRY_TRAIT)),
         );
 
         let from_yeet_expr = self.wrap_in_try_constructor(

compiler/rustc_ast_lowering/src/lib.rs

@@ -38,8 +38,9 @@
 #![recursion_limit = "256"]
 // tidy-alphabetical-end
 
+use std::borrow::Cow;
 use std::mem;
-use std::sync::{Arc, LazyLock};
+use std::sync::Arc;
 
 use rustc_ast::mut_visit::{self, MutVisitor};
 use rustc_ast::node_id::NodeMap;
@@ -325,25 +326,19 @@ struct LoweringContext<'a, 'hir> {
     attribute_parser: AttributeParser<'hir>,
 }
 
-macro_rules! allow {
-    ($($name:ident: $list:expr;)*) => {
-        $( static $name: LazyLock<Arc<[Symbol]>> = LazyLock::new(|| $list.into()); )*
-    }
-}
-
-allow! {
-    ALLOW_CONTRACTS: [sym::contracts_internals];
-    ALLOW_TRY_TRAIT: [sym::try_trait_v2, sym::try_trait_v2_residual, sym::yeet_desugar_details];
-    ALLOW_PATTERN_TYPE: [sym::pattern_types, sym::pattern_type_range_trait];
-    ALLOW_GEN_FUTURE: [sym::gen_future];
-    ALLOW_GEN_FUTURE_WITH_ASYNC_FN_TRACK_CALLER: [sym::gen_future, sym::closure_track_caller];
-    ALLOW_FOR_AWAIT: [sym::async_gen_internals, sym::async_iterator];
-    ALLOW_ASYNC_FN_TRAITS: [sym::async_fn_traits];
-    ALLOW_ASYNC_GEN: [sym::async_gen_internals];
-    // FIXME(gen_blocks): how does `closure_track_caller`/`async_fn_track_caller`
-    // interact with `gen`/`async gen` blocks
-    ALLOW_ASYNC_ITERATOR: [sym::gen_future, sym::async_iterator];
-}
+const ALLOW_CONTRACTS: &[Symbol] = &[sym::contracts_internals];
+const ALLOW_TRY_TRAIT: &[Symbol] =
+    &[sym::try_trait_v2, sym::try_trait_v2_residual, sym::yeet_desugar_details];
+const ALLOW_PATTERN_TYPE: &[Symbol] = &[sym::pattern_types, sym::pattern_type_range_trait];
+const ALLOW_GEN_FUTURE: &[Symbol] = &[sym::gen_future];
+const ALLOW_GEN_FUTURE_WITH_ASYNC_FN_TRACK_CALLER: &[Symbol] =
+    &[sym::gen_future, sym::closure_track_caller];
+const ALLOW_FOR_AWAIT: &[Symbol] = &[sym::async_gen_internals, sym::async_iterator];
+const ALLOW_ASYNC_FN_TRAITS: &[Symbol] = &[sym::async_fn_traits];
+const ALLOW_ASYNC_GEN: &[Symbol] = &[sym::async_gen_internals];
+// FIXME(gen_blocks): how does `closure_track_caller`/`async_fn_track_caller`
+// interact with `gen`/`async gen` blocks
+const ALLOW_ASYNC_ITERATOR: &[Symbol] = &[sym::gen_future, sym::async_iterator];
 
 impl<'a, 'hir> LoweringContext<'a, 'hir> {
     fn new(tcx: TyCtxt<'hir>, resolver: &'a ResolverAstLowering<'hir>, owner: NodeId) -> Self {
@@ -383,11 +378,11 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         self.tcx.dcx()
     }
 
-    fn allow_gen_future(&self) -> &Arc<[Symbol]> {
+    fn allow_gen_future(&self) -> Cow<'static, [Symbol]> {
         if self.tcx.features().async_fn_track_caller() {
-            &ALLOW_GEN_FUTURE_WITH_ASYNC_FN_TRACK_CALLER
+            Cow::Borrowed(ALLOW_GEN_FUTURE_WITH_ASYNC_FN_TRACK_CALLER)
         } else {
-            &ALLOW_GEN_FUTURE
+            Cow::Borrowed(ALLOW_GEN_FUTURE)
         }
     }
 }
@@ -1053,7 +1048,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         &self,
         reason: DesugaringKind,
         span: Span,
-        allow_internal_unstable: Option<Arc<[Symbol]>>,
+        allow_internal_unstable: Option<Cow<'static, [Symbol]>>,
     ) -> Span {
         self.tcx.with_stable_hashing_context(|hcx| {
             span.mark_with_reason(allow_internal_unstable, reason, span.edition(), hcx)
@@ -2095,7 +2090,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         let (opaque_ty_node_id, allowed_features) = match coro.kind {
             CoroutineKind::Async | CoroutineKind::Gen => (coro.return_impl_trait_id, None),
             CoroutineKind::AsyncGen => {
-                (coro.return_impl_trait_id, Some(Arc::clone(&ALLOW_ASYNC_ITERATOR)))
+                (coro.return_impl_trait_id, Some(Cow::Borrowed(ALLOW_ASYNC_ITERATOR)))
             }
         };
 

compiler/rustc_ast_lowering/src/pat.rs

@@ -1,4 +1,4 @@
-use std::sync::Arc;
+use std::borrow::Cow;
 
 use rustc_ast::*;
 use rustc_hir::attrs::lang_items::LangItem;
@@ -482,7 +482,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         let unstable_span = self.mark_span_with_reason(
             DesugaringKind::PatTyRange,
             span,
-            Some(Arc::clone(&crate::ALLOW_PATTERN_TYPE)),
+            Some(Cow::Borrowed(crate::ALLOW_PATTERN_TYPE)),
         );
         let anon_const = self.with_new_scopes(span, |this| {
             let def_id = this.local_def_id(e.id);
@@ -535,7 +535,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         let unstable_span = self.mark_span_with_reason(
             DesugaringKind::PatTyRange,
             self.lower_span(span),
-            Some(Arc::clone(&crate::ALLOW_PATTERN_TYPE)),
+            Some(Cow::Borrowed(crate::ALLOW_PATTERN_TYPE)),
         );
         let span = self.lower_span(base_type);
 

compiler/rustc_ast_lowering/src/path.rs

@@ -1,4 +1,4 @@
-use std::sync::Arc;
+use std::borrow::Cow;
 
 use rustc_ast::{self as ast, *};
 use rustc_errors::StashKey;
@@ -75,7 +75,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         let bound_modifier_allowed_features = if let Res::Def(DefKind::Trait, async_def_id) = res
             && self.tcx.async_fn_trait_kind_from_def_id(async_def_id).is_some()
         {
-            Some(Arc::clone(&crate::ALLOW_ASYNC_FN_TRAITS))
+            Some(Cow::Borrowed(crate::ALLOW_ASYNC_FN_TRAITS))
         } else {
             None
         };
@@ -260,7 +260,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         // Additional features ungated with a bound modifier like `async`.
         // This is passed down to the implicit associated type binding in
         // parenthesized bounds.
-        bound_modifier_allowed_features: Option<Arc<[Symbol]>>,
+        bound_modifier_allowed_features: Option<Cow<'static, [Symbol]>>,
     ) -> hir::PathSegment<'hir> {
         debug!("path_span: {:?}, lower_path_segment(segment: {:?})", path_span, segment);
         let (mut generic_args, infer_args) = if let Some(generic_args) = segment.args.as_deref() {
@@ -507,7 +507,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         &mut self,
         data: &ParenthesizedArgs,
         itctx: ImplTraitContext,
-        bound_modifier_allowed_features: Option<Arc<[Symbol]>>,
+        bound_modifier_allowed_features: Option<Cow<'static, [Symbol]>>,
     ) -> (GenericArgsCtor<'hir>, bool) {
         // Switch to `PassThrough` mode for anonymous lifetimes; this
         // means that we permit things like `&Ref<T>`, where `Ref` has

compiler/rustc_data_structures/src/stable_hash.rs

@@ -428,6 +428,13 @@ impl<T: ?Sized + StableHash> StableHash for ::std::sync::Arc<T> {
     }
 }
 
+impl<B: ?Sized + StableHash + ToOwned> StableHash for ::std::borrow::Cow<'_, B> {
+    #[inline]
+    fn stable_hash<Hcx: StableHashCtxt>(&self, hcx: &mut Hcx, hasher: &mut StableHasher) {
+        (**self).stable_hash(hcx, hasher);
+    }
+}
+
 impl StableHash for str {
     #[inline]
     fn stable_hash<Hcx: StableHashCtxt>(&self, hcx: &mut Hcx, hasher: &mut StableHasher) {

compiler/rustc_expand/src/base.rs

@@ -1,4 +1,5 @@
 use std::any::Any;
+use std::borrow::Cow;
 use std::default::Default;
 use std::iter;
 use std::path::PathBuf;
@@ -777,7 +778,7 @@ pub struct SyntaxExtension {
     /// Span of the macro definition.
     pub span: Span,
     /// List of unstable features that are treated as stable inside this macro.
-    pub allow_internal_unstable: Option<Arc<[Symbol]>>,
+    pub allow_internal_unstable: Option<Cow<'static, [Symbol]>>,
     /// The macro's stability info.
     pub stability: Option<Stability>,
     /// The macro's deprecation info.
@@ -913,7 +914,9 @@ impl SyntaxExtension {
             span,
             allow_internal_unstable: (!allow_internal_unstable.is_empty())
                 // FIXME(jdonszelmann): avoid the into_iter/collect?
-                .then(|| allow_internal_unstable.iter().map(|i| i.0).collect::<Vec<_>>().into()),
+                .then(|| {
+                    Cow::Owned(allow_internal_unstable.iter().map(|i| i.0).collect::<Vec<_>>())
+                }),
             stability,
             deprecation: find_attr!(
                 attrs,
@@ -1045,7 +1048,7 @@ pub trait ResolverExpand {
         &mut self,
         call_site: Span,
         pass: AstPass,
-        features: &[Symbol],
+        features: &'static [Symbol],
         parent_module_id: Option<NodeId>,
     ) -> LocalExpnId;
 

compiler/rustc_resolve/src/macros.rs

@@ -1,6 +1,7 @@
 //! A bunch of methods and structures more or less related to resolving macros and
 //! interface provided by `Resolver` to macro expander.
 
+use std::borrow::Cow;
 use std::mem;
 use std::sync::Arc;
 
@@ -226,7 +227,7 @@ impl<'ra, 'tcx> ResolverExpand for Resolver<'ra, 'tcx> {
         &mut self,
         call_site: Span,
         pass: AstPass,
-        features: &[Symbol],
+        features: &'static [Symbol],
         parent_module_id: Option<NodeId>,
     ) -> LocalExpnId {
         let parent_module = parent_module_id
@@ -237,7 +238,7 @@ impl<'ra, 'tcx> ResolverExpand for Resolver<'ra, 'tcx> {
                     ExpnKind::AstPass(pass),
                     call_site,
                     self.tcx.sess.edition(),
-                    features.into(),
+                    Cow::Borrowed(features),
                     None,
                     parent_module,
                 ),

compiler/rustc_span/src/hygiene.rs

@@ -24,9 +24,9 @@
 // because getting it wrong can lead to nested `HygieneData::with` calls that
 // trigger runtime aborts. (Fortunately these are obvious and easy to fix.)
 
+use std::borrow::Cow;
 use std::cell::RefCell;
 use std::hash::Hash;
-use std::sync::Arc;
 use std::{fmt, iter, mem};
 
 use rustc_data_structures::fingerprint::Fingerprint;
@@ -963,7 +963,7 @@ impl Span {
     /// allowed inside this span.
     pub fn mark_with_reason(
         self,
-        allow_internal_unstable: Option<Arc<[Symbol]>>,
+        allow_internal_unstable: Option<Cow<'static, [Symbol]>>,
         reason: DesugaringKind,
         edition: Edition,
         hcx: impl StableHashCtxt,
@@ -1019,7 +1019,7 @@ pub struct ExpnData {
     /// 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<Arc<[Symbol]>>,
+    pub allow_internal_unstable: Option<Cow<'static, [Symbol]>>,
     /// Edition of the crate in which the macro is defined.
     pub edition: Edition,
     /// The `DefId` of the macro being invoked,
@@ -1048,7 +1048,7 @@ impl ExpnData {
         parent: ExpnId,
         call_site: Span,
         def_site: Span,
-        allow_internal_unstable: Option<Arc<[Symbol]>>,
+        allow_internal_unstable: Option<Cow<'static, [Symbol]>>,
         edition: Edition,
         macro_def_id: Option<DefId>,
         parent_module: Option<ModId>,
@@ -1103,7 +1103,7 @@ impl ExpnData {
         kind: ExpnKind,
         call_site: Span,
         edition: Edition,
-        allow_internal_unstable: Arc<[Symbol]>,
+        allow_internal_unstable: Cow<'static, [Symbol]>,
         macro_def_id: Option<DefId>,
         parent_module: Option<ModId>,
     ) -> ExpnData {