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]>

1 files changed, 2 insertions, 1 deletions

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" ]