Fix use tree desugaring

crates/ra_hir/src/nameres/tests.rs

@@ -78,6 +78,35 @@ fn item_map_smoke_test() {
     );
 }
 
+#[test]
+fn use_trees() {
+    let (item_map, module_id) = item_map(
+        "
+        //- /lib.rs
+        mod foo;
+
+        use crate::foo::bar::{Baz, Quux};
+        <|>
+
+        //- /foo/mod.rs
+        pub mod bar;
+
+        //- /foo/bar.rs
+        pub struct Baz;
+        pub enum Quux {};
+    ",
+    );
+    check_module_item_map(
+        &item_map,
+        module_id,
+        "
+            Baz: t v
+            Quux: t
+            foo: t
+        ",
+    );
+}
+
 #[test]
 fn re_exports() {
     let (item_map, module_id) = item_map(

crates/ra_hir/src/path.rs

@@ -150,7 +150,7 @@ fn convert_path(prefix: Option<Path>, path: &ast::Path) -> Option<Path> {
     let prefix = if let Some(qual) = path.qualifier() {
         Some(convert_path(prefix, qual)?)
     } else {
-        None
+        prefix
     };
     let segment = path.segment()?;
     let res = match segment.kind()? {