resolver: Move local_modules from ResolverArenas to Resolver

Thus avoiding a `RefCell`.

compiler/rustc_resolve/src/check_unused.rs

@@ -507,7 +507,7 @@ impl Resolver<'_, '_> {
 
         let unused_imports = visitor.unused_imports;
         let mut check_redundant_imports = FxIndexSet::default();
-        for module in self.arenas.local_modules().iter() {
+        for module in &self.local_modules {
             for (_key, resolution) in self.resolutions(*module).borrow().iter() {
                 if let Some(binding) = resolution.borrow().best_binding()
                     && let NameBindingKind::Import { import, .. } = binding.kind

compiler/rustc_resolve/src/imports.rs

@@ -8,7 +8,7 @@ use rustc_data_structures::intern::Interned;
 use rustc_errors::codes::*;
 use rustc_errors::{Applicability, MultiSpan, pluralize, struct_span_code_err};
 use rustc_hir::def::{self, DefKind, PartialRes};
-use rustc_hir::def_id::DefId;
+use rustc_hir::def_id::{DefId, LocalDefIdMap};
 use rustc_middle::metadata::{ModChild, Reexport};
 use rustc_middle::span_bug;
 use rustc_middle::ty::Visibility;
@@ -572,9 +572,11 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
     }
 
     pub(crate) fn finalize_imports(&mut self) {
-        for module in self.arenas.local_modules().iter() {
-            self.finalize_resolutions_in(*module);
+        let mut module_children = Default::default();
+        for module in &self.local_modules {
+            self.finalize_resolutions_in(*module, &mut module_children);
         }
+        self.module_children = module_children;
 
         let mut seen_spans = FxHashSet::default();
         let mut errors = vec![];
@@ -651,7 +653,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
     }
 
     pub(crate) fn lint_reexports(&mut self, exported_ambiguities: FxHashSet<NameBinding<'ra>>) {
-        for module in self.arenas.local_modules().iter() {
+        for module in &self.local_modules {
             for (key, resolution) in self.resolutions(*module).borrow().iter() {
                 let resolution = resolution.borrow();
                 let Some(binding) = resolution.best_binding() else { continue };
@@ -1548,7 +1550,11 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
 
     // Miscellaneous post-processing, including recording re-exports,
     // reporting conflicts, and reporting unresolved imports.
-    fn finalize_resolutions_in(&mut self, module: Module<'ra>) {
+    fn finalize_resolutions_in(
+        &self,
+        module: Module<'ra>,
+        module_children: &mut LocalDefIdMap<Vec<ModChild>>,
+    ) {
         // Since import resolution is finished, globs will not define any more names.
         *module.globs.borrow_mut(self) = Vec::new();
 
@@ -1573,7 +1579,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
 
         if !children.is_empty() {
             // Should be fine because this code is only called for local modules.
-            self.module_children.insert(def_id.expect_local(), children);
+            module_children.insert(def_id.expect_local(), children);
         }
     }
 }

compiler/rustc_resolve/src/lib.rs

@@ -1145,6 +1145,8 @@ pub struct Resolver<'ra, 'tcx> {
     /// some AST passes can generate identifiers that only resolve to local or
     /// lang items.
     empty_module: Module<'ra>,
+    /// All local modules, including blocks.
+    local_modules: Vec<Module<'ra>>,
     /// Eagerly populated map of all local non-block modules.
     local_module_map: FxIndexMap<LocalDefId, Module<'ra>>,
     /// Lazily populated cache of modules loaded from external crates.
@@ -1298,7 +1300,6 @@ pub struct Resolver<'ra, 'tcx> {
 #[derive(Default)]
 pub struct ResolverArenas<'ra> {
     modules: TypedArena<ModuleData<'ra>>,
-    local_modules: RefCell<Vec<Module<'ra>>>,
     imports: TypedArena<ImportData<'ra>>,
     name_resolutions: TypedArena<RefCell<NameResolution<'ra>>>,
     ast_paths: TypedArena<ast::Path>,
@@ -1341,28 +1342,20 @@ impl<'ra> ResolverArenas<'ra> {
         span: Span,
         no_implicit_prelude: bool,
     ) -> Module<'ra> {
-        let (def_id, self_binding) = match kind {
-            ModuleKind::Def(def_kind, def_id, _) => (
-                Some(def_id),
-                Some(self.new_pub_res_binding(Res::Def(def_kind, def_id), span, LocalExpnId::ROOT)),
-            ),
-            ModuleKind::Block => (None, None),
+        let self_binding = match kind {
+            ModuleKind::Def(def_kind, def_id, _) => {
+                Some(self.new_pub_res_binding(Res::Def(def_kind, def_id), span, LocalExpnId::ROOT))
+            }
+            ModuleKind::Block => None,
         };
-        let module = Module(Interned::new_unchecked(self.modules.alloc(ModuleData::new(
+        Module(Interned::new_unchecked(self.modules.alloc(ModuleData::new(
             parent,
             kind,
             expn_id,
             span,
             no_implicit_prelude,
             self_binding,
-        ))));
-        if def_id.is_none_or(|def_id| def_id.is_local()) {
-            self.local_modules.borrow_mut().push(module);
-        }
-        module
-    }
-    fn local_modules(&'ra self) -> std::cell::Ref<'ra, Vec<Module<'ra>>> {
-        self.local_modules.borrow()
+        ))))
     }
     fn alloc_name_binding(&'ra self, name_binding: NameBindingData<'ra>) -> NameBinding<'ra> {
         Interned::new_unchecked(self.dropless.alloc(name_binding))
@@ -1505,7 +1498,6 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         arenas: &'ra ResolverArenas<'ra>,
     ) -> Resolver<'ra, 'tcx> {
         let root_def_id = CRATE_DEF_ID.to_def_id();
-        let mut local_module_map = FxIndexMap::default();
         let graph_root = arenas.new_module(
             None,
             ModuleKind::Def(DefKind::Mod, root_def_id, None),
@@ -1513,7 +1505,8 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             crate_span,
             attr::contains_name(attrs, sym::no_implicit_prelude),
         );
-        local_module_map.insert(CRATE_DEF_ID, graph_root);
+        let local_modules = vec![graph_root];
+        let local_module_map = FxIndexMap::from_iter([(CRATE_DEF_ID, graph_root)]);
         let empty_module = arenas.new_module(
             None,
             ModuleKind::Def(DefKind::Mod, root_def_id, None),
@@ -1591,6 +1584,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             module_children: Default::default(),
             trait_map: NodeMap::default(),
             empty_module,
+            local_modules,
             local_module_map,
             extern_module_map: Default::default(),
             block_map: Default::default(),
@@ -1694,6 +1688,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         no_implicit_prelude: bool,
     ) -> Module<'ra> {
         let module = self.arenas.new_module(parent, kind, expn_id, span, no_implicit_prelude);
+        self.local_modules.push(module);
         if let Some(def_id) = module.opt_def_id() {
             self.local_module_map.insert(def_id.expect_local(), module);
         }