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, 54 insertions, 0 deletions

diff --git a/crates/ra_ide_api/src/completion/snapshots/completion_item__completes_prelude.snap b/crates/ra_ide_api/src/completion/snapshots/completion_item__completes_prelude.snap
new file mode 100644
index 000000000..2b5a1a8ea
--- /dev/null
+++ b/crates/ra_ide_api/src/completion/snapshots/completion_item__completes_prelude.snap
@@ -0,0 +1,54 @@
+---
+created: "2019-02-13T19:52:43.734834624Z"
+creator: [email protected]
+source: crates/ra_ide_api/src/completion/completion_item.rs
+expression: kind_completions
+---
+[
+    CompletionItem {
+        completion_kind: Reference,
+        label: "Option",
+        kind: Some(
+            Struct
+        ),
+        detail: None,
+        documentation: None,
+        lookup: None,
+        insert_text: None,
+        insert_text_format: PlainText,
+        source_range: [18; 18),
+        text_edit: None
+    },
+    CompletionItem {
+        completion_kind: Reference,
+        label: "foo",
+        kind: Some(
+            Function
+        ),
+        detail: Some(
+            "fn foo()"
+        ),
+        documentation: None,
+        lookup: None,
+        insert_text: Some(
+            "foo()$0"
+        ),
+        insert_text_format: Snippet,
+        source_range: [18; 18),
+        text_edit: None
+    },
+    CompletionItem {
+        completion_kind: Reference,
+        label: "std",
+        kind: Some(
+            Module
+        ),
+        detail: None,
+        documentation: None,
+        lookup: None,
+        insert_text: None,
+        insert_text_format: PlainText,
+        source_range: [18; 18),
+        text_edit: None
+    }
+]