2 files changed, 44 insertions, 9 deletions

diff --git a/crates/ra_hir_def/src/nameres/collector.rs b/crates/ra_hir_def/src/nameres/collector.rs
index 30664278e..37d0f3093 100644
--- a/crates/ra_hir_def/src/nameres/collector.rs
+++ b/crates/ra_hir_def/src/nameres/collector.rs
@@ -20,7 +20,8 @@ use crate::{
     },
     path::{Path, PathKind},
     AdtId, AstId, AstItemDef, ConstId, CrateModuleId, EnumId, EnumVariantId, FunctionId,
-    LocationCtx, ModuleDefId, ModuleId, StaticId, StructId, TraitId, TypeAliasId, UnionId,
+    LocationCtx, ModuleDefId, ModuleId, StaticId, StructId, StructOrUnionId, TraitId, TypeAliasId,
+    UnionId,
 };
 
 pub(super) fn collect_defs(db: &impl DefDatabase2, mut def_map: CrateDefMap) -> CrateDefMap {
@@ -36,11 +37,12 @@ pub(super) fn collect_defs(db: &impl DefDatabase2, mut def_map: CrateDefMap) ->
         );
 
         // look for the prelude
-        if def_map.prelude.is_none() {
-            let map = db.crate_def_map(dep.crate_id);
-            if map.prelude.is_some() {
-                def_map.prelude = map.prelude;
-            }
+        // If the dependency defines a prelude, we overwrite an already defined
+        // prelude. This is necessary to import the "std" prelude if a crate
+        // depends on both "core" and "std".
+        let dep_def_map = db.crate_def_map(dep.crate_id);
+        if dep_def_map.prelude.is_some() {
+            def_map.prelude = dep_def_map.prelude;
         }
     }
 
@@ -665,12 +667,14 @@ where
                 PerNs::values(FunctionId::from_ast_id(ctx, ast_id).into())
             }
             raw::DefKind::Struct(ast_id) => {
-                let s = StructId::from_ast_id(ctx, ast_id).into();
+                let id = StructOrUnionId::from_ast_id(ctx, ast_id).into();
+                let s = StructId(id).into();
                 PerNs::both(s, s)
             }
             raw::DefKind::Union(ast_id) => {
-                let s = UnionId::from_ast_id(ctx, ast_id).into();
-                PerNs::both(s, s)
+                let id = StructOrUnionId::from_ast_id(ctx, ast_id).into();
+                let u = UnionId(id).into();
+                PerNs::both(u, u)
             }
             raw::DefKind::Enum(ast_id) => PerNs::types(EnumId::from_ast_id(ctx, ast_id).into()),
             raw::DefKind::Const(ast_id) => PerNs::values(ConstId::from_ast_id(ctx, ast_id).into()),
diff --git a/crates/ra_hir_def/src/nameres/tests.rs b/crates/ra_hir_def/src/nameres/tests.rs
index 52bd0aa91..256f7d4be 100644
--- a/crates/ra_hir_def/src/nameres/tests.rs
+++ b/crates/ra_hir_def/src/nameres/tests.rs
@@ -464,6 +464,37 @@ fn values_dont_shadow_extern_crates() {
 }
 
 #[test]
+fn std_prelude_takes_precedence_above_core_prelude() {
+    let map = def_map(
+        r#"
+        //- /main.rs crate:main deps:core,std
+        use {Foo, Bar};
+
+        //- /std.rs crate:std deps:core
+        #[prelude_import]
+        pub use self::prelude::*;
+        mod prelude {
+            pub struct Foo;
+            pub use core::prelude::Bar;
+        }
+
+        //- /core.rs crate:core
+        #[prelude_import]
+        pub use self::prelude::*;
+        mod prelude {
+            pub struct Bar;
+        }
+        "#,
+    );
+
+    assert_snapshot!(map, @r###"
+        ⋮crate
+        ⋮Bar: t v
+        ⋮Foo: t v
+    "###);
+}
+
+#[test]
 fn cfg_not_test() {
     let map = def_map(
         r#"