Don't allocate DefDatabase::crate_lang_items if its empty

crates/hir-def/src/attr.rs

@@ -355,7 +355,7 @@ fn parse_comma_sep<S>(subtree: &tt::Subtree<S>) -> Vec<SmolStr> {
 }
 
 impl AttrsWithOwner {
-    pub(crate) fn attrs_with_owner(db: &dyn DefDatabase, owner: AttrDefId) -> Self {
+    pub fn attrs_with_owner(db: &dyn DefDatabase, owner: AttrDefId) -> Self {
         Self { attrs: db.attrs(owner), owner }
     }
 

crates/hir-def/src/db.rs

@@ -214,10 +214,6 @@ fn fields_attrs_source_map(
     #[salsa::invoke(lang_item::lang_attr_query)]
     fn lang_attr(&self, def: AttrDefId) -> Option<LangItem>;
 
-    #[salsa::transparent]
-    #[salsa::invoke(AttrsWithOwner::attrs_with_owner)]
-    fn attrs_with_owner(&self, def: AttrDefId) -> AttrsWithOwner;
-
     // endregion:attrs
 
     #[salsa::invoke(LangItems::lang_item_query)]
@@ -241,7 +237,7 @@ fn fields_attrs_source_map(
     // endregion:visibilities
 
     #[salsa::invoke(LangItems::crate_lang_items_query)]
-    fn crate_lang_items(&self, krate: CrateId) -> Arc<LangItems>;
+    fn crate_lang_items(&self, krate: CrateId) -> Option<Arc<LangItems>>;
 
     fn crate_supports_no_std(&self, crate_id: CrateId) -> bool;
 }

crates/hir-def/src/lang_item.rs

@@ -87,7 +87,10 @@ pub fn target(&self, item: LangItem) -> Option<LangItemTarget> {
     }
 
     /// Salsa query. This will look for lang items in a specific crate.
-    pub(crate) fn crate_lang_items_query(db: &dyn DefDatabase, krate: CrateId) -> Arc<LangItems> {
+    pub(crate) fn crate_lang_items_query(
+        db: &dyn DefDatabase,
+        krate: CrateId,
+    ) -> Option<Arc<LangItems>> {
         let _p = profile::span("crate_lang_items_query");
 
         let mut lang_items = LangItems::default();
@@ -150,7 +153,11 @@ pub(crate) fn crate_lang_items_query(db: &dyn DefDatabase, krate: CrateId) -> Ar
             }
         }
 
-        Arc::new(lang_items)
+        if lang_items.items.is_empty() {
+            None
+        } else {
+            Some(Arc::new(lang_items))
+        }
     }
 
     /// Salsa query. Look for a lang item, starting from the specified crate and recursively
@@ -161,9 +168,9 @@ pub(crate) fn lang_item_query(
         item: LangItem,
     ) -> Option<LangItemTarget> {
         let _p = profile::span("lang_item_query");
-        let lang_items = db.crate_lang_items(start_crate);
-        let start_crate_target = lang_items.items.get(&item);
-        if let Some(&target) = start_crate_target {
+        if let Some(target) =
+            db.crate_lang_items(start_crate).and_then(|it| it.items.get(&item).copied())
+        {
             return Some(target);
         }
         db.crate_graph()[start_crate]

crates/hir/src/attrs.rs

@@ -35,7 +35,7 @@ macro_rules! impl_has_attrs {
         impl HasAttrs for $def {
             fn attrs(self, db: &dyn HirDatabase) -> AttrsWithOwner {
                 let def = AttrDefId::$def_id(self.into());
-                db.attrs_with_owner(def)
+                AttrsWithOwner::attrs_with_owner(db.upcast(), def)
             }
             fn attr_id(self) -> AttrDefId {
                 AttrDefId::$def_id(self.into())