From 8bff414abcd2ab8c3487085bb58cd5b8bea5436a Mon Sep 17 00:00:00 2001
From: Chayim Refael Friedman <chayimfr@gmail.com>
Date: Fri, 25 Apr 2025 17:18:14 +0300
Subject: [PATCH] Preallocate `parser::Input`

---
 crates/parser/src/input.rs                  | 9 ++++++++-
 crates/parser/src/shortcuts.rs              | 2 +-
 crates/syntax-bridge/src/to_parser_input.rs | 2 +-
 3 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/crates/parser/src/input.rs b/crates/parser/src/input.rs
index cabdff214d..4490956f97 100644
--- a/crates/parser/src/input.rs
+++ b/crates/parser/src/input.rs
@@ -12,7 +12,6 @@ type bits = u64;
 /// `Tokens` doesn't include whitespace and comments. Main input to the parser.
 ///
 /// Struct of arrays internally, but this shouldn't really matter.
-#[derive(Default)]
 pub struct Input {
     kind: Vec<SyntaxKind>,
     joint: Vec<bits>,
@@ -21,6 +20,14 @@ pub struct Input {
 
 /// `pub` impl used by callers to create `Tokens`.
 impl Input {
+    #[inline]
+    pub fn with_capacity(capacity: usize) -> Self {
+        Self {
+            kind: Vec::with_capacity(capacity),
+            joint: Vec::with_capacity(capacity / size_of::<bits>()),
+            contextual_kind: Vec::with_capacity(capacity),
+        }
+    }
     #[inline]
     pub fn push(&mut self, kind: SyntaxKind) {
         self.push_impl(kind, SyntaxKind::EOF)
diff --git a/crates/parser/src/shortcuts.rs b/crates/parser/src/shortcuts.rs
index 32569d5c3f..e2baec890c 100644
--- a/crates/parser/src/shortcuts.rs
+++ b/crates/parser/src/shortcuts.rs
@@ -27,7 +27,7 @@ pub enum StrStep<'a> {
 impl LexedStr<'_> {
     pub fn to_input(&self, edition: Edition) -> crate::Input {
         let _p = tracing::info_span!("LexedStr::to_input").entered();
-        let mut res = crate::Input::default();
+        let mut res = crate::Input::with_capacity(self.len());
         let mut was_joint = false;
         for i in 0..self.len() {
             let kind = self.kind(i);
diff --git a/crates/syntax-bridge/src/to_parser_input.rs b/crates/syntax-bridge/src/to_parser_input.rs
index 0dcb2be316..021dc6595f 100644
--- a/crates/syntax-bridge/src/to_parser_input.rs
+++ b/crates/syntax-bridge/src/to_parser_input.rs
@@ -12,7 +12,7 @@ pub fn to_parser_input<Ctx: Copy + fmt::Debug + PartialEq + Eq + Hash>(
     buffer: tt::TokenTreesView<'_, SpanData<Ctx>>,
     span_to_edition: &mut dyn FnMut(Ctx) -> Edition,
 ) -> parser::Input {
-    let mut res = parser::Input::default();
+    let mut res = parser::Input::with_capacity(buffer.len());
 
     let mut current = buffer.cursor();
     let mut syntax_context_to_edition_cache = FxHashMap::default();