3 files changed, 66 insertions, 8 deletions

diff --git a/crates/ra_hir_def/src/nameres/collector.rs b/crates/ra_hir_def/src/nameres/collector.rs
index 7e6083961..37d0f3093 100644
--- a/crates/ra_hir_def/src/nameres/collector.rs
+++ b/crates/ra_hir_def/src/nameres/collector.rs
@@ -1,8 +1,9 @@
 //! FIXME: write short doc here
 
 use hir_expand::{
+    builtin_macro::find_builtin_macro,
     name::{self, AsName, Name},
-    HirFileId, MacroCallId, MacroCallLoc, MacroDefId, MacroFileKind,
+    HirFileId, MacroCallId, MacroCallLoc, MacroDefId, MacroDefKind, MacroFileKind,
 };
 use ra_cfg::CfgOptions;
 use ra_db::{CrateId, FileId};
@@ -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;
         }
     }
 
@@ -691,10 +693,30 @@ where
     fn collect_macro(&mut self, mac: &raw::MacroData) {
         let ast_id = AstId::new(self.file_id, mac.ast_id);
 
+        // Case 0: builtin macros
+        if mac.builtin {
+            if let Some(name) = &mac.name {
+                let krate = self.def_collector.def_map.krate;
+                if let Some(macro_id) = find_builtin_macro(name, krate, ast_id) {
+                    self.def_collector.define_macro(
+                        self.module_id,
+                        name.clone(),
+                        macro_id,
+                        mac.export,
+                    );
+                    return;
+                }
+            }
+        }
+
         // Case 1: macro rules, define a macro in crate-global mutable scope
         if is_macro_rules(&mac.path) {
             if let Some(name) = &mac.name {
-                let macro_id = MacroDefId { ast_id, krate: self.def_collector.def_map.krate };
+                let macro_id = MacroDefId {
+                    ast_id,
+                    krate: self.def_collector.def_map.krate,
+                    kind: MacroDefKind::Declarative,
+                };
                 self.def_collector.define_macro(self.module_id, name.clone(), macro_id, mac.export);
             }
             return;
diff --git a/crates/ra_hir_def/src/nameres/raw.rs b/crates/ra_hir_def/src/nameres/raw.rs
index 369376f30..f52002bc0 100644
--- a/crates/ra_hir_def/src/nameres/raw.rs
+++ b/crates/ra_hir_def/src/nameres/raw.rs
@@ -200,6 +200,7 @@ pub(super) struct MacroData {
     pub(super) path: Path,
     pub(super) name: Option<Name>,
     pub(super) export: bool,
+    pub(super) builtin: bool,
 }
 
 struct RawItemsCollector {
@@ -367,7 +368,11 @@ impl RawItemsCollector {
         // FIXME: cfg_attr
         let export = m.attrs().filter_map(|x| x.simple_name()).any(|name| name == "macro_export");
 
-        let m = self.raw_items.macros.alloc(MacroData { ast_id, path, name, export });
+        // FIXME: cfg_attr
+        let builtin =
+            m.attrs().filter_map(|x| x.simple_name()).any(|name| name == "rustc_builtin_macro");
+
+        let m = self.raw_items.macros.alloc(MacroData { ast_id, path, name, export, builtin });
         self.push_item(current_module, attrs, RawItemKind::Macro(m));
     }
 
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#"