perf: Pre-allocate some buffers in parsing

Author: Veykril

crates/parser/src/input.rs

@@ -97,7 +97,7 @@ impl Input {
         let b_idx = n % (bits::BITS as usize);
         (idx, b_idx)
     }
-    fn len(&self) -> usize {
+    pub fn len(&self) -> usize {
         self.kind.len()
     }
 }

crates/parser/src/lexed_str.rs

@@ -150,7 +150,12 @@ struct Converter<'a> {
 impl<'a> Converter<'a> {
     fn new(edition: Edition, text: &'a str) -> Self {
         Self {
-            res: LexedStr { text, kind: Vec::new(), start: Vec::new(), error: Vec::new() },
+            res: LexedStr {
+                text,
+                kind: Vec::with_capacity(text.len() / 3),
+                start: Vec::with_capacity(text.len() / 3),
+                error: Vec::new(),
+            },
             offset: 0,
             edition,
         }

crates/parser/src/parser.rs

@@ -32,7 +32,7 @@ const PARSER_STEP_LIMIT: usize = if cfg!(debug_assertions) { 150_000 } else { 15
 
 impl<'t> Parser<'t> {
     pub(super) fn new(inp: &'t Input) -> Parser<'t> {
-        Parser { inp, pos: 0, events: Vec::new(), steps: Cell::new(0) }
+        Parser { inp, pos: 0, events: Vec::with_capacity(2 * inp.len()), steps: Cell::new(0) }
     }
 
     pub(crate) fn finish(self) -> Vec<Event> {

crates/span/src/ast_id.rs

@@ -603,8 +603,9 @@ impl AstIdMap {
         // After all, the block will then contain the *outer* item, so we allocate
         // an ID for it anyway.
         let mut blocks = Vec::new();
-        let mut curr_layer = vec![(node.clone(), None)];
-        let mut next_layer = vec![];
+        let mut curr_layer = Vec::with_capacity(32);
+        curr_layer.push((node.clone(), None));
+        let mut next_layer = Vec::with_capacity(32);
         while !curr_layer.is_empty() {
             curr_layer.drain(..).for_each(|(node, parent_idx)| {
                 let mut preorder = node.preorder();