Auto merge of #30294 - jseyfried:fix_shadowed_use_visibility, r=nrc

This fixes a bug in which the visibility of a use declaration defining a name in one namespace (e.g. the value namespace) is overridden by a later use declaration defining the same name in the other namespace (e.g. the type namespace). For example,
```rust
fn f() {}
pub mod bar {}

mod foo {
    use f; // This import should not be visible outside `foo`,
    pub use bar as f; // but it visible outside of `foo` because of this import.
}

fn main() { foo::f(); }
```
As the example demonstrates, this is a [breaking-change], but it looks unlikely to cause breakage in practice, and any breakage can be fixed by correcting visibility modifiers.

Author: bors

src/librustc_resolve/build_reduced_graph.rs

@@ -16,7 +16,7 @@
 use DefModifiers;
 use resolve_imports::ImportDirective;
 use resolve_imports::ImportDirectiveSubclass::{self, SingleImport, GlobImport};
-use resolve_imports::ImportResolution;
+use resolve_imports::{ImportResolution, ImportResolutionPerNamespace};
 use Module;
 use Namespace::{TypeNS, ValueNS};
 use NameBindings;
@@ -822,22 +822,23 @@ impl<'a, 'b:'a, 'tcx:'b> GraphBuilder<'a, 'b, 'tcx> {
 
                 let mut import_resolutions = module_.import_resolutions.borrow_mut();
                 match import_resolutions.get_mut(&target) {
-                    Some(resolution) => {
+                    Some(resolution_per_ns) => {
                         debug!("(building import directive) bumping reference");
-                        resolution.outstanding_references += 1;
+                        resolution_per_ns.outstanding_references += 1;
 
                         // the source of this name is different now
-                        resolution.type_id = id;
-                        resolution.value_id = id;
-                        resolution.is_public = is_public;
+                        let resolution =
+                            ImportResolution { id: id, is_public: is_public, target: None };
+                        resolution_per_ns[TypeNS] = resolution.clone();
+                        resolution_per_ns[ValueNS] = resolution;
                         return;
                     }
                     None => {}
                 }
                 debug!("(building import directive) creating new");
-                let mut resolution = ImportResolution::new(id, is_public);
-                resolution.outstanding_references = 1;
-                import_resolutions.insert(target, resolution);
+                let mut import_resolution_per_ns = ImportResolutionPerNamespace::new(id, is_public);
+                import_resolution_per_ns.outstanding_references = 1;
+                import_resolutions.insert(target, import_resolution_per_ns);
             }
             GlobImport => {
                 // Set the glob flag. This tells us that we don't know the

src/librustc_resolve/lib.rs

@@ -96,7 +96,7 @@ use std::mem::replace;
 use std::rc::{Rc, Weak};
 use std::usize;
 
-use resolve_imports::{Target, ImportDirective, ImportResolution};
+use resolve_imports::{Target, ImportDirective, ImportResolutionPerNamespace};
 use resolve_imports::Shadowable;
 
 // NB: This module needs to be declared first so diagnostics are
@@ -328,7 +328,7 @@ fn resolve_error<'b, 'a: 'b, 'tcx: 'a>(resolver: &'b Resolver<'a, 'tcx>,
                                              .import_resolutions
                                              .borrow()
                                              .get(&name) {
-                let item = resolver.ast_map.expect_item(directive.value_id);
+                let item = resolver.ast_map.expect_item(directive.value_ns.id);
                 resolver.session.span_note(item.span, "constant imported here");
             }
         }
@@ -793,7 +793,7 @@ pub struct Module {
     anonymous_children: RefCell<NodeMap<Rc<Module>>>,
 
     // The status of resolving each import in this module.
-    import_resolutions: RefCell<HashMap<Name, ImportResolution>>,
+    import_resolutions: RefCell<HashMap<Name, ImportResolutionPerNamespace>>,
 
     // The number of unresolved globs that this module exports.
     glob_count: Cell<usize>,
@@ -912,7 +912,7 @@ bitflags! {
 // Records a possibly-private value, type, or module definition.
 #[derive(Debug)]
 struct NsDef {
-    modifiers: DefModifiers, // see note in ImportResolution about how to use this
+    modifiers: DefModifiers, // see note in ImportResolutionPerNamespace about how to use this
     def_or_module: DefOrModule,
     span: Option<Span>,
 }
@@ -1491,7 +1491,7 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
         // adjacent import statements are processed as though they mutated the
         // current scope.
         if let Some(import_resolution) = module_.import_resolutions.borrow().get(&name) {
-            match (*import_resolution).target_for_namespace(namespace) {
+            match import_resolution[namespace].target.clone() {
                 None => {
                     // Not found; continue.
                     debug!("(resolving item in lexical scope) found import resolution, but not \
@@ -1501,7 +1501,7 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                 Some(target) => {
                     debug!("(resolving item in lexical scope) using import resolution");
                     // track used imports and extern crates as well
-                    let id = import_resolution.id(namespace);
+                    let id = import_resolution[namespace].id;
                     self.used_imports.insert((id, namespace));
                     self.record_import_use(id, name);
                     if let Some(DefId{krate: kid, ..}) = target.target_module.def_id() {
@@ -1712,21 +1712,23 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
 
         // Check the list of resolved imports.
         match module_.import_resolutions.borrow().get(&name) {
-            Some(import_resolution) if allow_private_imports || import_resolution.is_public => {
+            Some(import_resolution) if allow_private_imports ||
+                                       import_resolution[namespace].is_public => {
 
-                if import_resolution.is_public && import_resolution.outstanding_references != 0 {
+                if import_resolution[namespace].is_public &&
+                   import_resolution.outstanding_references != 0 {
                     debug!("(resolving name in module) import unresolved; bailing out");
                     return Indeterminate;
                 }
-                match import_resolution.target_for_namespace(namespace) {
+                match import_resolution[namespace].target.clone() {
                     None => {
                         debug!("(resolving name in module) name found, but not in namespace {:?}",
                                namespace);
                     }
                     Some(target) => {
                         debug!("(resolving name in module) resolved to import");
                         // track used imports and extern crates as well
-                        let id = import_resolution.id(namespace);
+                        let id = import_resolution[namespace].id;
                         self.used_imports.insert((id, namespace));
                         self.record_import_use(id, name);
                         if let Some(DefId{krate: kid, ..}) = target.target_module.def_id() {
@@ -3651,17 +3653,17 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
 
             // Look for imports.
             for (_, import) in search_module.import_resolutions.borrow().iter() {
-                let target = match import.target_for_namespace(TypeNS) {
+                let target = match import.type_ns.target {
                     None => continue,
-                    Some(target) => target,
+                    Some(ref target) => target,
                 };
                 let did = match target.binding.def() {
                     Some(DefTrait(trait_def_id)) => trait_def_id,
                     Some(..) | None => continue,
                 };
                 if self.trait_item_map.contains_key(&(name, did)) {
                     add_trait_info(&mut found_traits, did, name);
-                    let id = import.type_id;
+                    let id = import.type_ns.id;
                     self.used_imports.insert((id, TypeNS));
                     let trait_name = self.get_trait_name(did);
                     self.record_import_use(id, trait_name);
@@ -3734,7 +3736,7 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
         let import_resolutions = module_.import_resolutions.borrow();
         for (&name, import_resolution) in import_resolutions.iter() {
             let value_repr;
-            match import_resolution.target_for_namespace(ValueNS) {
+            match import_resolution.value_ns.target {
                 None => {
                     value_repr = "".to_string();
                 }
@@ -3745,7 +3747,7 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
             }
 
             let type_repr;
-            match import_resolution.target_for_namespace(TypeNS) {
+            match import_resolution.type_ns.target {
                 None => {
                     type_repr = "".to_string();
                 }

src/librustc_resolve/record_exports.rs

@@ -130,13 +130,14 @@ impl<'a, 'b, 'tcx> ExportRecorder<'a, 'b, 'tcx> {
 
     fn add_exports_for_module(&mut self, exports: &mut Vec<Export>, module_: &Module) {
         for (name, import_resolution) in module_.import_resolutions.borrow().iter() {
-            if !import_resolution.is_public {
-                continue;
-            }
             let xs = [TypeNS, ValueNS];
             for &ns in &xs {
-                match import_resolution.target_for_namespace(ns) {
-                    Some(target) => {
+                if !import_resolution[ns].is_public {
+                    continue;
+                }
+
+                match import_resolution[ns].target {
+                    Some(ref target) => {
                         debug!("(computing exports) maybe export '{}'", name);
                         self.add_export_of_namebinding(exports, *name, &target.binding)
                     }