7 files changed, 99 insertions, 12 deletions

diff --git a/crates/ra_hir/src/marks.rs b/crates/ra_hir/src/marks.rs
index 50d4e824c..16852a6a1 100644
--- a/crates/ra_hir/src/marks.rs
+++ b/crates/ra_hir/src/marks.rs
@@ -6,4 +6,5 @@ test_utils::marks!(
     type_var_resolves_to_int_var
     glob_enum
     glob_across_crates
+    std_prelude
 );
diff --git a/crates/ra_hir/src/nameres.rs b/crates/ra_hir/src/nameres.rs
index ffb20d564..2ba6038c6 100644
--- a/crates/ra_hir/src/nameres.rs
+++ b/crates/ra_hir/src/nameres.rs
@@ -34,6 +34,10 @@ use crate::{
 /// module, the set of visible items.
 #[derive(Default, Debug, PartialEq, Eq)]
 pub struct ItemMap {
+    /// The prelude module for this crate. This either comes from an import
+    /// marked with the `prelude_import` attribute, or (in the normal case) from
+    /// a dependency (`std` or `core`).
+    prelude: Option<Module>,
     pub(crate) extern_prelude: FxHashMap<Name, ModuleDef>,
     per_module: ArenaMap<ModuleId, ModuleScope>,
 }
@@ -211,6 +215,13 @@ where
             if let Some(module) = dep.krate.root_module(self.db) {
                 self.result.extern_prelude.insert(dep.name.clone(), module.into());
             }
+            // look for the prelude
+            if self.result.prelude.is_none() {
+                let item_map = self.db.item_map(dep.krate);
+                if item_map.prelude.is_some() {
+                    self.result.prelude = item_map.prelude;
+                }
+            }
         }
     }
 
@@ -279,7 +290,10 @@ where
             log::debug!("glob import: {:?}", import);
             match def.take_types() {
                 Some(ModuleDef::Module(m)) => {
-                    if m.krate != self.krate {
+                    if import.is_prelude {
+                        tested_by!(std_prelude);
+                        self.result.prelude = Some(m);
+                    } else if m.krate != self.krate {
                         tested_by!(glob_across_crates);
                         // glob import from other crate => we can just import everything once
                         let item_map = self.db.item_map(m.krate);
@@ -434,12 +448,40 @@ impl ItemMap {
         self.resolve_path_fp(db, original_module, path).0
     }
 
-    pub(crate) fn resolve_name_in_module(&self, module: Module, name: &Name) -> PerNs<ModuleDef> {
+    fn resolve_in_prelude(
+        &self,
+        db: &impl PersistentHirDatabase,
+        original_module: Module,
+        name: &Name,
+    ) -> PerNs<ModuleDef> {
+        if let Some(prelude) = self.prelude {
+            let resolution = if prelude.krate == original_module.krate {
+                self[prelude.module_id].items.get(name).cloned()
+            } else {
+                db.item_map(prelude.krate)[prelude.module_id].items.get(name).cloned()
+            };
+            resolution.map(|r| r.def).unwrap_or_else(PerNs::none)
+        } else {
+            PerNs::none()
+        }
+    }
+
+    pub(crate) fn resolve_name_in_module(
+        &self,
+        db: &impl PersistentHirDatabase,
+        module: Module,
+        name: &Name,
+    ) -> PerNs<ModuleDef> {
+        // Resolve in:
+        //  - current module / scope
+        //  - extern prelude
+        //  - std prelude
         let from_scope = self[module.module_id].items.get(name).map_or(PerNs::none(), |it| it.def);
         let from_extern_prelude =
             self.extern_prelude.get(name).map_or(PerNs::none(), |&it| PerNs::types(it));
+        let from_prelude = self.resolve_in_prelude(db, module, name);
 
-        from_scope.or(from_extern_prelude)
+        from_scope.or(from_extern_prelude).or(from_prelude)
     }
 
     // Returns Yes if we are sure that additions to `ItemMap` wouldn't change
@@ -459,7 +501,7 @@ impl ItemMap {
                     Some((_, segment)) => segment,
                     None => return (PerNs::none(), ReachedFixedPoint::Yes),
                 };
-                self.resolve_name_in_module(original_module, &segment.name)
+                self.resolve_name_in_module(db, original_module, &segment.name)
             }
             PathKind::Super => {
                 if let Some(p) = original_module.parent(db) {
diff --git a/crates/ra_hir/src/nameres/lower.rs b/crates/ra_hir/src/nameres/lower.rs
index 3cd496d7f..922dbe9c1 100644
--- a/crates/ra_hir/src/nameres/lower.rs
+++ b/crates/ra_hir/src/nameres/lower.rs
@@ -2,7 +2,7 @@ use std::sync::Arc;
 
 use ra_syntax::{
     AstNode, SourceFile, TreeArc, AstPtr,
-    ast::{self, ModuleItemOwner, NameOwner},
+    ast::{self, ModuleItemOwner, NameOwner, AttrsOwner},
 };
 use ra_arena::{Arena, RawId, impl_arena_id, map::ArenaMap};
 use rustc_hash::FxHashMap;
@@ -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_prelude: bool,
     pub(super) is_extern_crate: bool,
 }
 
@@ -191,6 +192,7 @@ impl LoweredModule {
                         path,
                         alias,
                         is_glob: false,
+                        is_prelude: false,
                         is_extern_crate: true,
                     });
                 }
@@ -214,11 +216,14 @@ impl LoweredModule {
     }
 
     fn add_use_item(&mut self, source_map: &mut ImportSourceMap, item: &ast::UseItem) {
+        let is_prelude =
+            item.attrs().any(|attr| attr.as_atom().map(|s| s == "prelude_import").unwrap_or(false));
         Path::expand_use_item(item, |path, segment, alias| {
             let import = self.imports.alloc(ImportData {
                 path,
                 alias,
                 is_glob: segment.is_none(),
+                is_prelude,
                 is_extern_crate: false,
             });
             if let Some(segment) = segment {
diff --git a/crates/ra_hir/src/nameres/tests.rs b/crates/ra_hir/src/nameres/tests.rs
index 6dbe759d1..68ebe963a 100644
--- a/crates/ra_hir/src/nameres/tests.rs
+++ b/crates/ra_hir/src/nameres/tests.rs
@@ -297,6 +297,43 @@ fn module_resolution_works_for_non_standard_filenames() {
 }
 
 #[test]
+fn std_prelude() {
+    covers!(std_prelude);
+    let mut db = MockDatabase::with_files(
+        "
+        //- /main.rs
+        use Foo::*;
+
+        //- /lib.rs
+        mod prelude;
+        #[prelude_import]
+        use prelude::*;
+
+        //- /prelude.rs
+        pub enum Foo { Bar, Baz };
+    ",
+    );
+    db.set_crate_graph_from_fixture(crate_graph! {
+        "main": ("/main.rs", ["test_crate"]),
+        "test_crate": ("/lib.rs", []),
+    });
+    let main_id = db.file_id_of("/main.rs");
+
+    let module = crate::source_binder::module_from_file_id(&db, main_id).unwrap();
+    let krate = module.krate(&db).unwrap();
+    let item_map = db.item_map(krate);
+
+    check_module_item_map(
+        &item_map,
+        module.module_id,
+        "
+            Bar: t v
+            Baz: t v
+        ",
+    );
+}
+
+#[test]
 fn name_res_works_for_broken_modules() {
     covers!(name_res_works_for_broken_modules);
     let (item_map, module_id) = item_map(
diff --git a/crates/ra_hir/src/resolve.rs b/crates/ra_hir/src/resolve.rs
index 40c860cf4..fde4d6580 100644
--- a/crates/ra_hir/src/resolve.rs
+++ b/crates/ra_hir/src/resolve.rs
@@ -56,10 +56,10 @@ pub enum Resolution {
 }
 
 impl Resolver {
-    pub fn resolve_name(&self, name: &Name) -> PerNs<Resolution> {
+    pub fn resolve_name(&self, db: &impl HirDatabase, name: &Name) -> PerNs<Resolution> {
         let mut resolution = PerNs::none();
         for scope in self.scopes.iter().rev() {
-            resolution = resolution.or(scope.resolve_name(name));
+            resolution = resolution.or(scope.resolve_name(db, name));
             if resolution.is_both() {
                 return resolution;
             }
@@ -69,9 +69,9 @@ impl Resolver {
 
     pub fn resolve_path(&self, db: &impl HirDatabase, path: &Path) -> PerNs<Resolution> {
         if let Some(name) = path.as_ident() {
-            self.resolve_name(name)
+            self.resolve_name(db, name)
         } else if path.is_self() {
-            self.resolve_name(&Name::self_param())
+            self.resolve_name(db, &Name::self_param())
         } else {
             let (item_map, module) = match self.module() {
                 Some(m) => m,
@@ -143,13 +143,13 @@ impl Resolver {
 }
 
 impl Scope {
-    fn resolve_name(&self, name: &Name) -> PerNs<Resolution> {
+    fn resolve_name(&self, db: &impl HirDatabase, name: &Name) -> PerNs<Resolution> {
         match self {
             Scope::ModuleScope(m) => {
                 if let Some(KnownName::SelfParam) = name.as_known_name() {
                     PerNs::types(Resolution::Def(m.module.into()))
                 } else {
-                    m.item_map.resolve_name_in_module(m.module, name).map(Resolution::Def)
+                    m.item_map.resolve_name_in_module(db, m.module, name).map(Resolution::Def)
                 }
             }
             Scope::GenericParams(gp) => match gp.find_by_name(name) {
diff --git a/crates/ra_syntax/src/ast/generated.rs b/crates/ra_syntax/src/ast/generated.rs
index 5df3f2ccf..7c5e8ce5e 100644
--- a/crates/ra_syntax/src/ast/generated.rs
+++ b/crates/ra_syntax/src/ast/generated.rs
@@ -4210,6 +4210,7 @@ impl ToOwned for UseItem {
 }
 
 
+impl ast::AttrsOwner for UseItem {}
 impl UseItem {
     pub fn use_tree(&self) -> Option<&UseTree> {
         super::child_opt(self)
diff --git a/crates/ra_syntax/src/grammar.ron b/crates/ra_syntax/src/grammar.ron
index 2e4b2d776..304bc5909 100644
--- a/crates/ra_syntax/src/grammar.ron
+++ b/crates/ra_syntax/src/grammar.ron
@@ -596,7 +596,8 @@ Grammar(
             options: [ "Pat", "TypeRef" ],
         ),
         "UseItem": (
-            options: [ "UseTree" ]
+            traits: ["AttrsOwner"],
+            options: [ "UseTree" ],
         ),
         "UseTree": (
             options: [ "Path", "UseTreeList", "Alias" ]