Merge #816

816: Prelude & Edition 2015 import resolution r=matklad a=flodiebold

I implemented the prelude import, but it turned out to be useless without being able to resolve any of the imports in the prelude :sweat_smile: So I had to add some edition handling and handle 2015-style imports (at least the simplified scheme proposed in rust-lang/rust#57745). So now finally `Option` resolves :smile: 

One remaining problem is that we don't actually know the edition for sysroot crates. They're currently hardcoded to 2015, but there's already a bunch of PRs upgrading the editions of various rustc crates, so we'll have to detect the edition somehow, or just change the hardcoding to 2018 later, I guess...

~Also currently missing is completion for prelude names, though that shouldn't be hard to add. And `Vec` still doesn't resolve, so I need to look into that.~

Co-authored-by: Florian Diebold <[email protected]>

2 files changed, 120 insertions, 8 deletions

diff --git a/crates/ra_hir/src/nameres/lower.rs b/crates/ra_hir/src/nameres/lower.rs
index 3cd496d7f..81d80654c 100644
--- a/crates/ra_hir/src/nameres/lower.rs
+++ b/crates/ra_hir/src/nameres/lower.rs
@@ -2,13 +2,13 @@ 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;
 
 use crate::{
-    SourceItemId, Path, PathKind, ModuleSource, Name,
+    SourceItemId, Path, 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_prelude: bool,
     pub(super) is_extern_crate: bool,
 }
 
@@ -179,18 +180,14 @@ impl LoweredModule {
                 self.add_use_item(source_map, it);
             }
             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 path = Path::from_name_ref(name_ref);
                     let alias = it.alias().and_then(|a| a.name()).map(AsName::as_name);
                     self.imports.alloc(ImportData {
                         path,
                         alias,
                         is_glob: false,
+                        is_prelude: false,
                         is_extern_crate: true,
                     });
                 }
@@ -214,11 +211,14 @@ 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..6402c89c0 100644
--- a/crates/ra_hir/src/nameres/tests.rs
+++ b/crates/ra_hir/src/nameres/tests.rs
@@ -266,6 +266,45 @@ fn glob_across_crates() {
 }
 
 #[test]
+fn edition_2015_imports() {
+    let mut db = MockDatabase::with_files(
+        "
+        //- /main.rs
+        mod foo;
+        mod bar;
+
+        //- /bar.rs
+        struct Bar;
+
+        //- /foo.rs
+        use bar::Bar;
+        use other_crate::FromLib;
+
+        //- /lib.rs
+        struct FromLib;
+    ",
+    );
+    db.set_crate_graph_from_fixture(crate_graph! {
+        "main": ("/main.rs", "2015", ["other_crate"]),
+        "other_crate": ("/lib.rs", "2018", []),
+    });
+    let foo_id = db.file_id_of("/foo.rs");
+
+    let module = crate::source_binder::module_from_file_id(&db, foo_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
+            FromLib: t v
+        ",
+    );
+}
+
+#[test]
 fn module_resolution_works_for_non_standard_filenames() {
     let mut db = MockDatabase::with_files(
         "
@@ -297,6 +336,43 @@ 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(
@@ -467,6 +543,42 @@ fn extern_crate_rename() {
 }
 
 #[test]
+fn extern_crate_rename_2015_edition() {
+    let mut db = 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;
+        ",
+    );
+    db.set_crate_graph_from_fixture(crate_graph! {
+        "main": ("/main.rs", "2015", ["alloc"]),
+        "alloc": ("/lib.rs", []),
+    });
+    let sync_id = db.file_id_of("/sync.rs");
+
+    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
+        ",
+    );
+}
+
+#[test]
 fn import_across_source_roots() {
     let mut db = MockDatabase::with_files(
         "