5 files changed, 127 insertions, 40 deletions

diff --git a/crates/ra_hir/src/code_model_api.rs b/crates/ra_hir/src/code_model_api.rs
index 92ab0f692..a58bf8f87 100644
--- a/crates/ra_hir/src/code_model_api.rs
+++ b/crates/ra_hir/src/code_model_api.rs
@@ -134,7 +134,7 @@ impl Module {
     }
 
     /// Returns the crate this module is part of.
-    pub fn krate(&self, _db: &impl HirDatabase) -> Option<Crate> {
+    pub fn krate(&self, _db: &impl PersistentHirDatabase) -> Option<Crate> {
         Some(self.krate)
     }
 
diff --git a/crates/ra_hir/src/nameres.rs b/crates/ra_hir/src/nameres.rs
index 04cc693b3..681aa9a67 100644
--- a/crates/ra_hir/src/nameres.rs
+++ b/crates/ra_hir/src/nameres.rs
@@ -34,6 +34,7 @@ use crate::{
 /// module, the set of visible items.
 #[derive(Default, Debug, PartialEq, Eq)]
 pub struct ItemMap {
+    pub(crate) extern_prelude: FxHashMap<Name, ModuleDef>,
     per_module: ArenaMap<ModuleId, ModuleScope>,
 }
 
@@ -204,6 +205,7 @@ where
     }
 
     pub(crate) fn resolve(mut self) -> ItemMap {
+        self.populate_extern_prelude();
         for (&module_id, items) in self.input.iter() {
             self.populate_module(module_id, Arc::clone(items));
         }
@@ -227,29 +229,19 @@ where
         self.result
     }
 
+    fn populate_extern_prelude(&mut self) {
+        for dep in self.krate.dependencies(self.db) {
+            log::debug!("crate dep {:?} -> {:?}", dep.name, dep.krate);
+            if let Some(module) = dep.krate.root_module(self.db) {
+                self.result
+                    .extern_prelude
+                    .insert(dep.name.clone(), module.into());
+            }
+        }
+    }
+
     fn populate_module(&mut self, module_id: ModuleId, input: Arc<LoweredModule>) {
         let mut module_items = ModuleScope::default();
-
-        // Populate extern crates prelude
-        {
-            let root_id = module_id.crate_root(&self.module_tree);
-            let file_id = root_id.file_id(&self.module_tree);
-            let crate_graph = self.db.crate_graph();
-            if let Some(crate_id) = crate_graph.crate_id_for_crate_root(file_id.as_original_file())
-            {
-                let krate = Crate { crate_id };
-                for dep in krate.dependencies(self.db) {
-                    if let Some(module) = dep.krate.root_module(self.db) {
-                        let def = module.into();
-                        self.add_module_item(
-                            &mut module_items,
-                            dep.name.clone(),
-                            PerNs::types(def),
-                        );
-                    }
-                }
-            };
-        }
         for (import_id, import_data) in input.imports.iter() {
             if let Some(last_segment) = import_data.path.segments.iter().last() {
                 if !import_data.is_glob {
@@ -327,7 +319,16 @@ where
                 .alias
                 .clone()
                 .unwrap_or_else(|| last_segment.name.clone());
-            log::debug!("resolved import {:?} ({:?}) to {:?}", name, import, def,);
+            log::debug!("resolved import {:?} ({:?}) to {:?}", name, import, def);
+
+            // extern crates in the crate root are special-cased to insert entries into the extern prelude: rust-lang/rust#54658
+            if let Some(root_module) = self.krate.root_module(self.db) {
+                if import.is_extern_crate && module_id == root_module.module_id {
+                    if let Some(def) = def.take_types() {
+                        self.result.extern_prelude.insert(name.clone(), def);
+                    }
+                }
+            }
             self.update(module_id, |items| {
                 let res = Resolution {
                     def,
@@ -389,24 +390,53 @@ impl ItemMap {
         original_module: Module,
         path: &Path,
     ) -> (PerNs<ModuleDef>, ReachedFixedPoint) {
-        let mut curr_per_ns: PerNs<ModuleDef> = PerNs::types(match path.kind {
-            PathKind::Crate => original_module.crate_root(db).into(),
-            PathKind::Self_ | PathKind::Plain => original_module.into(),
+        let mut segments = path.segments.iter().enumerate();
+        let mut curr_per_ns: PerNs<ModuleDef> = match path.kind {
+            PathKind::Crate => PerNs::types(original_module.crate_root(db).into()),
+            PathKind::Self_ => PerNs::types(original_module.into()),
+            PathKind::Plain => {
+                let segment = match segments.next() {
+                    Some((_, segment)) => segment,
+                    None => return (PerNs::none(), ReachedFixedPoint::Yes),
+                };
+                // Resolve in:
+                //  - current module / scope
+                //  - extern prelude
+                match self[original_module.module_id].items.get(&segment.name) {
+                    Some(res) if !res.def.is_none() => res.def,
+                    _ => {
+                        if let Some(def) = self.extern_prelude.get(&segment.name) {
+                            PerNs::types(*def)
+                        } else {
+                            return (PerNs::none(), ReachedFixedPoint::No);
+                        }
+                    }
+                }
+            }
             PathKind::Super => {
                 if let Some(p) = original_module.parent(db) {
-                    p.into()
+                    PerNs::types(p.into())
                 } else {
                     log::debug!("super path in root module");
                     return (PerNs::none(), ReachedFixedPoint::Yes);
                 }
             }
             PathKind::Abs => {
-                // TODO: absolute use is not supported
-                return (PerNs::none(), ReachedFixedPoint::Yes);
+                // 2018-style absolute path -- only extern prelude
+                let segment = match segments.next() {
+                    Some((_, segment)) => segment,
+                    None => return (PerNs::none(), ReachedFixedPoint::Yes),
+                };
+                if let Some(def) = self.extern_prelude.get(&segment.name) {
+                    log::debug!("absolute path {:?} resolved to crate {:?}", path, def);
+                    PerNs::types(*def)
+                } else {
+                    return (PerNs::none(), ReachedFixedPoint::No); // extern crate declarations can add to the extern prelude
+                }
             }
-        });
+        };
 
-        for (i, segment) in path.segments.iter().enumerate() {
+        for (i, segment) in segments {
             let curr = match curr_per_ns.as_ref().take_types() {
                 Some(r) => r,
                 None => {
diff --git a/crates/ra_hir/src/nameres/lower.rs b/crates/ra_hir/src/nameres/lower.rs
index df87f520f..7e6e48ae0 100644
--- a/crates/ra_hir/src/nameres/lower.rs
+++ b/crates/ra_hir/src/nameres/lower.rs
@@ -8,7 +8,7 @@ use ra_arena::{Arena, RawId, impl_arena_id, map::ArenaMap};
 use rustc_hash::FxHashMap;
 
 use crate::{
-    SourceItemId, Path, ModuleSource, Name,
+    SourceItemId, Path, PathKind, ModuleSource, Name,
     HirFileId, MacroCallLoc, AsName, PerNs, Function,
     ModuleDef, Module, Struct, Enum, Const, Static, Trait, Type,
     ids::LocationCtx, PersistentHirDatabase,
@@ -23,6 +23,7 @@ pub(super) struct ImportData {
     pub(super) path: Path,
     pub(super) alias: Option<Name>,
     pub(super) is_glob: bool,
+    pub(super) is_extern_crate: bool,
 }
 
 /// A set of items and imports declared inside a module, without relation to
@@ -186,8 +187,22 @@ impl LoweredModule {
             ast::ModuleItemKind::UseItem(it) => {
                 self.add_use_item(source_map, it);
             }
-            ast::ModuleItemKind::ExternCrateItem(_) => {
-                // TODO
+            ast::ModuleItemKind::ExternCrateItem(it) => {
+                // Lower `extern crate x` to `use ::x`. This is kind of cheating
+                // and only works if we always interpret absolute paths in the
+                // 2018 style; otherwise `::x` could also refer to a module in
+                // the crate root.
+                if let Some(name_ref) = it.name_ref() {
+                    let mut path = Path::from_name_ref(name_ref);
+                    path.kind = PathKind::Abs;
+                    let alias = it.alias().and_then(|a| a.name()).map(AsName::as_name);
+                    self.imports.alloc(ImportData {
+                        path,
+                        alias,
+                        is_glob: false,
+                        is_extern_crate: true,
+                    });
+                }
             }
             ast::ModuleItemKind::ConstDef(it) => {
                 if let Some(name) = it.name() {
@@ -215,6 +230,7 @@ impl LoweredModule {
                 path,
                 alias,
                 is_glob: segment.is_none(),
+                is_extern_crate: false,
             });
             if let Some(segment) = segment {
                 source_map.insert(import, segment)
diff --git a/crates/ra_hir/src/nameres/tests.rs b/crates/ra_hir/src/nameres/tests.rs
index 81c8a4f12..0654dbaa1 100644
--- a/crates/ra_hir/src/nameres/tests.rs
+++ b/crates/ra_hir/src/nameres/tests.rs
@@ -329,7 +329,49 @@ fn item_map_across_crates() {
         module.module_id,
         "
             Baz: t v
-            test_crate: t
+        ",
+    );
+}
+
+#[test]
+fn extern_crate_rename() {
+    let (mut db, sr) = MockDatabase::with_files(
+        "
+        //- /main.rs
+        extern crate alloc as alloc_crate;
+
+        mod alloc;
+        mod sync;
+
+        //- /sync.rs
+        use alloc_crate::Arc;
+
+        //- /lib.rs
+        struct Arc;
+    ",
+    );
+    let main_id = sr.files[RelativePath::new("/main.rs")];
+    let sync_id = sr.files[RelativePath::new("/sync.rs")];
+    let lib_id = sr.files[RelativePath::new("/lib.rs")];
+
+    let mut crate_graph = CrateGraph::default();
+    let main_crate = crate_graph.add_crate_root(main_id);
+    let lib_crate = crate_graph.add_crate_root(lib_id);
+    crate_graph
+        .add_dep(main_crate, "alloc".into(), lib_crate)
+        .unwrap();
+
+    db.set_crate_graph(Arc::new(crate_graph));
+
+    let module = crate::source_binder::module_from_file_id(&db, sync_id).unwrap();
+    let krate = module.krate(&db).unwrap();
+    let item_map = db.item_map(krate);
+
+    check_module_item_map(
+        &item_map,
+        module.module_id,
+        "
+            Arc: t v
         ",
     );
 }
@@ -361,8 +403,6 @@ fn import_across_source_roots() {
 
     let main_id = sr2.files[RelativePath::new("/main.rs")];
 
-    eprintln!("lib = {:?}, main = {:?}", lib_id, main_id);
-
     let mut crate_graph = CrateGraph::default();
     let main_crate = crate_graph.add_crate_root(main_id);
     let lib_crate = crate_graph.add_crate_root(lib_id);
@@ -381,7 +421,6 @@ fn import_across_source_roots() {
         module.module_id,
         "
             C: t v
-            test_crate: t
         ",
     );
 }
@@ -423,7 +462,6 @@ fn reexport_across_crates() {
         module.module_id,
         "
             Baz: t v
-            test_crate: t
         ",
     );
 }
diff --git a/crates/ra_hir/src/resolve.rs b/crates/ra_hir/src/resolve.rs
index 6c87d0df7..5ca7bacb5 100644
--- a/crates/ra_hir/src/resolve.rs
+++ b/crates/ra_hir/src/resolve.rs
@@ -197,7 +197,10 @@ impl Scope {
                     .entries()
                     .for_each(|(name, res)| {
                         f(name.clone(), res.def.map(Resolution::Def));
-                    })
+                    });
+                m.item_map.extern_prelude.iter().for_each(|(name, def)| {
+                    f(name.clone(), PerNs::types(Resolution::Def(*def)));
+                });
             }
             Scope::GenericParams(gp) => {
                 for param in &gp.params {