From 67b57f69cac1ccf7fad3986fc0c6ee2022eebd06 Mon Sep 17 00:00:00 2001
From: Vadim Petrochenkov <vadim.petrochenkov@gmail.com>
Date: Tue, 15 Jul 2025 23:42:35 +0300
Subject: resolve: Make disambiguators for underscore bindings module-local

---
 compiler/rustc_resolve/src/lib.rs | 33 +++++++++++++++------------------
 1 file changed, 15 insertions(+), 18 deletions(-)

(limited to 'compiler/rustc_resolve/src/lib.rs')

diff --git a/compiler/rustc_resolve/src/lib.rs b/compiler/rustc_resolve/src/lib.rs
index 0d41a822e8a..948b67a3798 100644
--- a/compiler/rustc_resolve/src/lib.rs
+++ b/compiler/rustc_resolve/src/lib.rs
@@ -532,15 +532,26 @@ struct BindingKey {
     /// identifier.
     ident: Ident,
     ns: Namespace,
-    /// 0 if ident is not `_`, otherwise a value that's unique to the specific
-    /// `_` in the expanded AST that introduced this binding.
+    /// When we add an underscore binding (with ident `_`) to some module, this field has
+    /// a non-zero value that uniquely identifies this binding in that module.
+    /// For non-underscore bindings this field is zero.
+    /// When a key is constructed for name lookup (as opposed to name definition), this field is
+    /// also zero, even for underscore names, so for underscores the lookup will never succeed.
     disambiguator: u32,
 }
 
 impl BindingKey {
     fn new(ident: Ident, ns: Namespace) -> Self {
-        let ident = ident.normalize_to_macros_2_0();
-        BindingKey { ident, ns, disambiguator: 0 }
+        BindingKey { ident: ident.normalize_to_macros_2_0(), ns, disambiguator: 0 }
+    }
+
+    fn new_disambiguated(
+        ident: Ident,
+        ns: Namespace,
+        disambiguator: impl FnOnce() -> u32,
+    ) -> BindingKey {
+        let disambiguator = if ident.name == kw::Underscore { disambiguator() } else { 0 };
+        BindingKey { ident: ident.normalize_to_macros_2_0(), ns, disambiguator }
     }
 }
 
@@ -1087,8 +1098,6 @@ pub struct Resolver<'ra, 'tcx> {
     extern_module_map: RefCell<FxIndexMap<DefId, Module<'ra>>>,
     binding_parent_modules: FxHashMap<NameBinding<'ra>, Module<'ra>>,
 
-    underscore_disambiguator: u32,
-
     /// Maps glob imports to the names of items actually imported.
     glob_map: FxIndexMap<LocalDefId, FxIndexSet<Symbol>>,
     glob_error: Option<ErrorGuaranteed>,
@@ -1500,7 +1509,6 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             extern_crate_map: Default::default(),
             module_children: Default::default(),
             trait_map: NodeMap::default(),
-            underscore_disambiguator: 0,
             empty_module,
             local_module_map,
             extern_module_map: Default::default(),
@@ -1881,17 +1889,6 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         import_ids
     }
 
-    fn new_disambiguated_key(&mut self, ident: Ident, ns: Namespace) -> BindingKey {
-        let ident = ident.normalize_to_macros_2_0();
-        let disambiguator = if ident.name == kw::Underscore {
-            self.underscore_disambiguator += 1;
-            self.underscore_disambiguator
-        } else {
-            0
-        };
-        BindingKey { ident, ns, disambiguator }
-    }
-
     fn resolutions(&mut self, module: Module<'ra>) -> &'ra Resolutions<'ra> {
         if module.populate_on_access.get() {
             module.populate_on_access.set(false);
-- 
cgit 1.4.1-3-g733a5