From f27268f319d402fcd68509e1836edaea8dc357ea Mon Sep 17 00:00:00 2001
From: Lukas Wirth <me@lukaswirth.dev>
Date: Thu, 12 Jun 2025 11:25:20 +0200
Subject: [PATCH] Ditch the unnecessary smallvec

---
 crates/hir-def/src/item_tree.rs       | 11 +++++------
 crates/hir-def/src/item_tree/lower.rs | 16 ++++++++++------
 2 files changed, 15 insertions(+), 12 deletions(-)

diff --git a/crates/hir-def/src/item_tree.rs b/crates/hir-def/src/item_tree.rs
index b295767399..9f8d7b9e31 100644
--- a/crates/hir-def/src/item_tree.rs
+++ b/crates/hir-def/src/item_tree.rs
@@ -53,7 +53,6 @@ use hir_expand::{
 use intern::Interned;
 use la_arena::Idx;
 use rustc_hash::FxHashMap;
-use smallvec::SmallVec;
 use span::{AstIdNode, Edition, ErasedFileAstId, FileAstId, SyntaxContext};
 use stdx::never;
 use syntax::{SyntaxKind, ast, match_ast};
@@ -89,11 +88,12 @@ impl fmt::Debug for RawVisibilityId {
 /// The item tree of a source file.
 #[derive(Debug, Default, Eq, PartialEq)]
 pub struct ItemTree {
-    top_level: SmallVec<[ModItemId; 1]>,
+    top_level: Box<[ModItemId]>,
     // Consider splitting this into top level RawAttrs and the map?
     attrs: FxHashMap<AttrOwner, RawAttrs>,
 
     vis: ItemVisibilities,
+    // FIXME: They values store the key, turn this into a FxHashSet<ModItem> instead?
     data: FxHashMap<FileAstId<ast::Item>, ModItem>,
 }
 
@@ -136,7 +136,7 @@ impl ItemTree {
             EMPTY
                 .get_or_init(|| {
                     Arc::new(ItemTree {
-                        top_level: SmallVec::new_const(),
+                        top_level: Box::new([]),
                         attrs: FxHashMap::default(),
                         data: FxHashMap::default(),
                         vis: ItemVisibilities { arena: Box::new([]) },
@@ -163,7 +163,7 @@ impl ItemTree {
             EMPTY
                 .get_or_init(|| {
                     Arc::new(ItemTree {
-                        top_level: SmallVec::new_const(),
+                        top_level: Box::new([]),
                         attrs: FxHashMap::default(),
                         data: FxHashMap::default(),
                         vis: ItemVisibilities { arena: Box::new([]) },
@@ -226,8 +226,7 @@ impl ItemTree {
     }
 
     fn shrink_to_fit(&mut self) {
-        let ItemTree { top_level, attrs, data, vis: _ } = self;
-        top_level.shrink_to_fit();
+        let ItemTree { top_level: _, attrs, data, vis: _ } = self;
         attrs.shrink_to_fit();
         data.shrink_to_fit();
     }
diff --git a/crates/hir-def/src/item_tree/lower.rs b/crates/hir-def/src/item_tree/lower.rs
index f3e71effe4..a7038356b3 100644
--- a/crates/hir-def/src/item_tree/lower.rs
+++ b/crates/hir-def/src/item_tree/lower.rs
@@ -33,6 +33,7 @@ pub(super) struct Ctx<'a> {
     source_ast_id_map: Arc<AstIdMap>,
     span_map: OnceCell<SpanMap>,
     file: HirFileId,
+    top_level: Vec<ModItemId>,
     visibilities: FxIndexSet<RawVisibility>,
 }
 
@@ -45,6 +46,7 @@ impl<'a> Ctx<'a> {
             file,
             span_map: OnceCell::new(),
             visibilities: FxIndexSet::default(),
+            top_level: Vec::new(),
         }
     }
 
@@ -53,14 +55,14 @@ impl<'a> Ctx<'a> {
     }
 
     pub(super) fn lower_module_items(mut self, item_owner: &dyn HasModuleItem) -> ItemTree {
-        self.tree.top_level =
-            item_owner.items().flat_map(|item| self.lower_mod_item(&item)).collect();
+        self.top_level = item_owner.items().flat_map(|item| self.lower_mod_item(&item)).collect();
         self.tree.vis.arena = self.visibilities.into_iter().collect();
+        self.tree.top_level = self.top_level.into_boxed_slice();
         self.tree
     }
 
     pub(super) fn lower_macro_stmts(mut self, stmts: ast::MacroStmts) -> ItemTree {
-        self.tree.top_level = stmts
+        self.top_level = stmts
             .statements()
             .filter_map(|stmt| {
                 match stmt {
@@ -84,18 +86,19 @@ impl<'a> Ctx<'a> {
             if let Some(call) = tail_macro.macro_call() {
                 cov_mark::hit!(macro_stmt_with_trailing_macro_expr);
                 if let Some(mod_item) = self.lower_mod_item(&call.into()) {
-                    self.tree.top_level.push(mod_item);
+                    self.top_level.push(mod_item);
                 }
             }
         }
 
         self.tree.vis.arena = self.visibilities.into_iter().collect();
+        self.tree.top_level = self.top_level.into_boxed_slice();
         self.tree
     }
 
     pub(super) fn lower_block(mut self, block: &ast::BlockExpr) -> ItemTree {
         self.tree.attrs.insert(AttrOwner::TopLevel, RawAttrs::new(self.db, block, self.span_map()));
-        self.tree.top_level = block
+        self.top_level = block
             .statements()
             .filter_map(|stmt| match stmt {
                 ast::Stmt::Item(item) => self.lower_mod_item(&item),
@@ -111,11 +114,12 @@ impl<'a> Ctx<'a> {
         if let Some(ast::Expr::MacroExpr(expr)) = block.tail_expr() {
             if let Some(call) = expr.macro_call() {
                 if let Some(mod_item) = self.lower_mod_item(&call.into()) {
-                    self.tree.top_level.push(mod_item);
+                    self.top_level.push(mod_item);
                 }
             }
         }
         self.tree.vis.arena = self.visibilities.into_iter().collect();
+        self.tree.top_level = self.top_level.into_boxed_slice();
         self.tree
     }