resolve: Collapse macro_rules scope chains on the fly

compiler/rustc_resolve/src/lib.rs

@@ -64,7 +64,7 @@ use diagnostics::{extend_span_to_previous_binding, find_span_of_binding_until_ne
 use diagnostics::{ImportSuggestion, LabelSuggestion, Suggestion};
 use imports::{Import, ImportKind, ImportResolver, NameResolution};
 use late::{HasGenericParams, PathSource, Rib, RibKind::*};
-use macros::{MacroRulesBinding, MacroRulesScope};
+use macros::{MacroRulesBinding, MacroRulesScope, MacroRulesScopeRef};
 
 type Res = def::Res<NodeId>;
 
@@ -100,7 +100,7 @@ impl Determinacy {
 enum Scope<'a> {
     DeriveHelpers(ExpnId),
     DeriveHelpersCompat,
-    MacroRules(MacroRulesScope<'a>),
+    MacroRules(MacroRulesScopeRef<'a>),
     CrateRoot,
     Module(Module<'a>),
     RegisteredAttrs,
@@ -133,18 +133,18 @@ enum ScopeSet {
 pub struct ParentScope<'a> {
     module: Module<'a>,
     expansion: ExpnId,
-    macro_rules: MacroRulesScope<'a>,
+    macro_rules: MacroRulesScopeRef<'a>,
     derives: &'a [ast::Path],
 }
 
 impl<'a> ParentScope<'a> {
     /// Creates a parent scope with the passed argument used as the module scope component,
     /// and other scope components set to default empty values.
-    pub fn module(module: Module<'a>) -> ParentScope<'a> {
+    pub fn module(module: Module<'a>, resolver: &Resolver<'a>) -> ParentScope<'a> {
         ParentScope {
             module,
             expansion: ExpnId::root(),
-            macro_rules: MacroRulesScope::Empty,
+            macro_rules: resolver.arenas.alloc_macro_rules_scope(MacroRulesScope::Empty),
             derives: &[],
         }
     }
@@ -974,7 +974,10 @@ pub struct Resolver<'a> {
     invocation_parent_scopes: FxHashMap<ExpnId, ParentScope<'a>>,
     /// `macro_rules` scopes *produced* by expanding the macro invocations,
     /// include all the `macro_rules` items and other invocations generated by them.
-    output_macro_rules_scopes: FxHashMap<ExpnId, MacroRulesScope<'a>>,
+    output_macro_rules_scopes: FxHashMap<ExpnId, MacroRulesScopeRef<'a>>,
+    /// References to all `MacroRulesScope::Invocation(invoc_id)`s, used to update such scopes
+    /// when their corresponding `invoc_id`s get expanded.
+    invocation_macro_rules_scopes: FxHashMap<ExpnId, FxHashSet<MacroRulesScopeRef<'a>>>,
     /// Helper attributes that are in scope for the given expansion.
     helper_attrs: FxHashMap<ExpnId, Vec<Ident>>,
 
@@ -1043,6 +1046,9 @@ impl<'a> ResolverArenas<'a> {
     fn alloc_name_resolution(&'a self) -> &'a RefCell<NameResolution<'a>> {
         self.name_resolutions.alloc(Default::default())
     }
+    fn alloc_macro_rules_scope(&'a self, scope: MacroRulesScope<'a>) -> MacroRulesScopeRef<'a> {
+        PtrKey(self.dropless.alloc(Cell::new(scope)))
+    }
     fn alloc_macro_rules_binding(
         &'a self,
         binding: MacroRulesBinding<'a>,
@@ -1230,14 +1236,11 @@ impl<'a> Resolver<'a> {
         let (registered_attrs, registered_tools) =
             macros::registered_attrs_and_tools(session, &krate.attrs);
 
-        let mut invocation_parent_scopes = FxHashMap::default();
-        invocation_parent_scopes.insert(ExpnId::root(), ParentScope::module(graph_root));
-
         let features = session.features_untracked();
         let non_macro_attr =
             |mark_used| Lrc::new(SyntaxExtension::non_macro_attr(mark_used, session.edition()));
 
-        Resolver {
+        let mut resolver = Resolver {
             session,
 
             definitions,
@@ -1304,8 +1307,9 @@ impl<'a> Resolver<'a> {
             dummy_ext_bang: Lrc::new(SyntaxExtension::dummy_bang(session.edition())),
             dummy_ext_derive: Lrc::new(SyntaxExtension::dummy_derive(session.edition())),
             non_macro_attrs: [non_macro_attr(false), non_macro_attr(true)],
-            invocation_parent_scopes,
+            invocation_parent_scopes: Default::default(),
             output_macro_rules_scopes: Default::default(),
+            invocation_macro_rules_scopes: Default::default(),
             helper_attrs: Default::default(),
             local_macro_def_scopes: FxHashMap::default(),
             name_already_seen: FxHashMap::default(),
@@ -1332,7 +1336,12 @@ impl<'a> Resolver<'a> {
             invocation_parents,
             next_disambiguator: Default::default(),
             trait_impl_items: Default::default(),
-        }
+        };
+
+        let root_parent_scope = ParentScope::module(graph_root, &resolver);
+        resolver.invocation_parent_scopes.insert(ExpnId::root(), root_parent_scope);
+
+        resolver
     }
 
     pub fn next_node_id(&mut self) -> NodeId {
@@ -1702,7 +1711,7 @@ impl<'a> Resolver<'a> {
                 }
                 Scope::DeriveHelpers(..) => Scope::DeriveHelpersCompat,
                 Scope::DeriveHelpersCompat => Scope::MacroRules(parent_scope.macro_rules),
-                Scope::MacroRules(macro_rules_scope) => match macro_rules_scope {
+                Scope::MacroRules(macro_rules_scope) => match macro_rules_scope.get() {
                     MacroRulesScope::Binding(binding) => {
                         Scope::MacroRules(binding.parent_macro_rules_scope)
                     }
@@ -3199,7 +3208,7 @@ impl<'a> Resolver<'a> {
             }
         };
         let module = self.get_module(module_id);
-        let parent_scope = &ParentScope::module(module);
+        let parent_scope = &ParentScope::module(module, self);
         let res = self.resolve_ast_path(&path, ns, parent_scope).map_err(|_| ())?;
         Ok((path, res))
     }