4 files changed, 27 insertions, 12 deletions

diff --git a/crates/ra_hir/src/attr.rs b/crates/ra_hir/src/attr.rs
index 84c36b8da..a8a7e9006 100644
--- a/crates/ra_hir/src/attr.rs
+++ b/crates/ra_hir/src/attr.rs
@@ -45,10 +45,15 @@ impl Attr {
 
     pub(crate) fn from_attrs_owner(
         file_id: HirFileId,
-        owner: &impl AttrsOwner,
+        owner: &dyn AttrsOwner,
         db: &impl AstDatabase,
-    ) -> Arc<[Attr]> {
-        owner.attrs().flat_map(|ast| Attr::from_src(Source { file_id, ast }, db)).collect()
+    ) -> Option<Arc<[Attr]>> {
+        let mut attrs = owner.attrs().peekable();
+        if attrs.peek().is_none() {
+            // Avoid heap allocation
+            return None;
+        }
+        Some(attrs.flat_map(|ast| Attr::from_src(Source { file_id, ast }, db)).collect())
     }
 
     pub(crate) fn is_simple_atom(&self, name: &str) -> bool {
diff --git a/crates/ra_hir/src/impl_block.rs b/crates/ra_hir/src/impl_block.rs
index 7877c3171..55dfc393b 100644
--- a/crates/ra_hir/src/impl_block.rs
+++ b/crates/ra_hir/src/impl_block.rs
@@ -213,7 +213,9 @@ impl ModuleImplBlocks {
             match item {
                 ast::ItemOrMacro::Item(ast::ModuleItem::ImplBlock(impl_block_ast)) => {
                     let attrs = Attr::from_attrs_owner(file_id, &impl_block_ast, db);
-                    if attrs.iter().any(|attr| attr.is_cfg_enabled(cfg_options) == Some(false)) {
+                    if attrs.map_or(false, |attrs| {
+                        attrs.iter().any(|attr| attr.is_cfg_enabled(cfg_options) == Some(false))
+                    }) {
                         continue;
                     }
 
@@ -228,7 +230,9 @@ impl ModuleImplBlocks {
                 ast::ItemOrMacro::Item(_) => (),
                 ast::ItemOrMacro::Macro(macro_call) => {
                     let attrs = Attr::from_attrs_owner(file_id, &macro_call, db);
-                    if attrs.iter().any(|attr| attr.is_cfg_enabled(cfg_options) == Some(false)) {
+                    if attrs.map_or(false, |attrs| {
+                        attrs.iter().any(|attr| attr.is_cfg_enabled(cfg_options) == Some(false))
+                    }) {
                         continue;
                     }
 
diff --git a/crates/ra_hir/src/nameres/collector.rs b/crates/ra_hir/src/nameres/collector.rs
index 1d79cbd8c..cef2dc9d2 100644
--- a/crates/ra_hir/src/nameres/collector.rs
+++ b/crates/ra_hir/src/nameres/collector.rs
@@ -7,7 +7,6 @@ use rustc_hash::FxHashMap;
 use test_utils::tested_by;
 
 use crate::{
-    attr::Attr,
     db::DefDatabase,
     ids::{AstItemDef, LocationCtx, MacroCallId, MacroCallLoc, MacroDefId, MacroFileKind},
     name::MACRO_RULES,
@@ -715,8 +714,12 @@ where
         }
     }
 
-    fn is_cfg_enabled(&self, attrs: &[Attr]) -> bool {
-        attrs.iter().all(|attr| attr.is_cfg_enabled(&self.def_collector.cfg_options) != Some(false))
+    fn is_cfg_enabled(&self, attrs: &raw::Attrs) -> bool {
+        attrs.as_ref().map_or(true, |attrs| {
+            attrs
+                .iter()
+                .all(|attr| attr.is_cfg_enabled(&self.def_collector.cfg_options) != Some(false))
+        })
     }
 }
 
diff --git a/crates/ra_hir/src/nameres/raw.rs b/crates/ra_hir/src/nameres/raw.rs
index f02d4eb7a..623b343c4 100644
--- a/crates/ra_hir/src/nameres/raw.rs
+++ b/crates/ra_hir/src/nameres/raw.rs
@@ -120,9 +120,12 @@ impl Index<Macro> for RawItems {
     }
 }
 
+// Avoid heap allocation on items without attributes.
+pub(super) type Attrs = Option<Arc<[Attr]>>;
+
 #[derive(Debug, PartialEq, Eq, Clone)]
 pub(super) struct RawItem {
-    pub(super) attrs: Arc<[Attr]>,
+    pub(super) attrs: Attrs,
     pub(super) kind: RawItemKind,
 }
 
@@ -390,7 +393,7 @@ impl<DB: AstDatabase> RawItemsCollector<&DB> {
     fn push_import(
         &mut self,
         current_module: Option<Module>,
-        attrs: Arc<[Attr]>,
+        attrs: Attrs,
         data: ImportData,
         source: ImportSourcePtr,
     ) {
@@ -399,7 +402,7 @@ impl<DB: AstDatabase> RawItemsCollector<&DB> {
         self.push_item(current_module, attrs, RawItemKind::Import(import))
     }
 
-    fn push_item(&mut self, current_module: Option<Module>, attrs: Arc<[Attr]>, kind: RawItemKind) {
+    fn push_item(&mut self, current_module: Option<Module>, attrs: Attrs, kind: RawItemKind) {
         match current_module {
             Some(module) => match &mut self.raw_items.modules[module] {
                 ModuleData::Definition { items, .. } => items,
@@ -410,7 +413,7 @@ impl<DB: AstDatabase> RawItemsCollector<&DB> {
         .push(RawItem { attrs, kind })
     }
 
-    fn parse_attrs(&self, item: &impl ast::AttrsOwner) -> Arc<[Attr]> {
+    fn parse_attrs(&self, item: &impl ast::AttrsOwner) -> Attrs {
         Attr::from_attrs_owner(self.file_id, item, self.db)
     }
 }