Auto merge of #31857 - jseyfried:fix_scoping, r=nikomatsakis

This fixes a bug (#31845) introduced in #31105 in which lexical scopes contain items from all anonymous module ancestors, even if the path to the anonymous module includes a normal module:
```rust
fn f() {
    fn g() {}
    mod foo {
        fn h() {
           g(); // This erroneously resolves on nightly
        }
    }
}
```

This is a [breaking-change] on nightly but not on stable or beta.
r? @nikomatsakis

src/librustc_resolve/lib.rs

@@ -731,8 +731,8 @@ enum RibKind<'a> {
     // We're in a constant item. Can't refer to dynamic stuff.
     ConstantItemRibKind,
 
-    // We passed through an anonymous module.
-    AnonymousModuleRibKind(Module<'a>),
+    // We passed through a module.
+    ModuleRibKind(Module<'a>),
 }
 
 #[derive(Copy, Clone)]
@@ -1680,16 +1680,20 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
     fn with_scope<F>(&mut self, id: NodeId, f: F)
         where F: FnOnce(&mut Resolver)
     {
-        let orig_module = self.current_module;
+        if let Some(module) = self.current_module.module_children.borrow().get(&id) {
+            // Move down in the graph.
+            let orig_module = ::std::mem::replace(&mut self.current_module, module);
+            self.value_ribs.push(Rib::new(ModuleRibKind(module)));
+            self.type_ribs.push(Rib::new(ModuleRibKind(module)));
 
-        // Move down in the graph.
-        if let Some(module) = orig_module.module_children.borrow().get(&id) {
-            self.current_module = module;
+            f(self);
+
+            self.current_module = orig_module;
+            self.value_ribs.pop();
+            self.type_ribs.pop();
+        } else {
+            f(self);
         }
-
-        f(self);
-
-        self.current_module = orig_module;
     }
 
     /// Searches the current set of local scopes for labels.
@@ -2266,8 +2270,8 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
 
         if let Some(anonymous_module) = anonymous_module {
             debug!("(resolving block) found anonymous module, moving down");
-            self.value_ribs.push(Rib::new(AnonymousModuleRibKind(anonymous_module)));
-            self.type_ribs.push(Rib::new(AnonymousModuleRibKind(anonymous_module)));
+            self.value_ribs.push(Rib::new(ModuleRibKind(anonymous_module)));
+            self.type_ribs.push(Rib::new(ModuleRibKind(anonymous_module)));
             self.current_module = anonymous_module;
         } else {
             self.value_ribs.push(Rib::new(NormalRibKind));
@@ -2811,8 +2815,9 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
         }
 
         if check_ribs {
-            if let Some(def) = self.resolve_identifier_in_local_ribs(identifier, namespace) {
-                return Some(def);
+            match self.resolve_identifier_in_local_ribs(identifier, namespace, record_used) {
+                Some(def) => return Some(def),
+                None => {}
             }
         }
 
@@ -2844,7 +2849,7 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
             Def::Local(_, node_id) => {
                 for rib in ribs {
                     match rib.kind {
-                        NormalRibKind | AnonymousModuleRibKind(..) => {
+                        NormalRibKind | ModuleRibKind(..) => {
                             // Nothing to do. Continue.
                         }
                         ClosureRibKind(function_id) => {
@@ -2893,7 +2898,7 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                 for rib in ribs {
                     match rib.kind {
                         NormalRibKind | MethodRibKind | ClosureRibKind(..) |
-                        AnonymousModuleRibKind(..) => {
+                        ModuleRibKind(..) => {
                             // Nothing to do. Continue.
                         }
                         ItemRibKind => {
@@ -3024,7 +3029,8 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
 
     fn resolve_identifier_in_local_ribs(&mut self,
                                         ident: hir::Ident,
-                                        namespace: Namespace)
+                                        namespace: Namespace,
+                                        record_used: bool)
                                         -> Option<LocalDef> {
         // Check the local set of ribs.
         let name = match namespace { ValueNS => ident.name, TypeNS => ident.unhygienic_name };
@@ -3051,16 +3057,18 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                 }
             }
 
-            if let AnonymousModuleRibKind(module) = self.get_ribs(namespace)[i].kind {
+            if let ModuleRibKind(module) = self.get_ribs(namespace)[i].kind {
                 if let Success(binding) = self.resolve_name_in_module(module,
                                                                       ident.unhygienic_name,
                                                                       namespace,
                                                                       true,
-                                                                      true) {
+                                                                      record_used) {
                     if let Some(def) = binding.def() {
                         return Some(LocalDef::from_def(def));
                     }
                 }
+                // We can only see through anonymous modules
+                if module.def.is_some() { return None; }
             }
         }
 

src/test/compile-fail/issue-31845.rs

@@ -0,0 +1,22 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Checks lexical scopes cannot see through normal module boundries
+
+fn f() {
+    fn g() {}
+    mod foo {
+        fn h() {
+           g(); //~ ERROR unresolved name
+        }
+    }
+}
+
+fn main() {}

src/test/compile-fail/lint-unused-imports.rs

@@ -69,6 +69,13 @@ mod bar {
     }
 }
 
+fn g() {
+    use self::g; //~ ERROR unused import
+    fn f() {
+        self::g();
+    }
+}
+
 fn main() {
     cal(foo::Point{x:3, y:9});
     let mut a = 3;