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perf(parser): fast-path leaf expressions before delimiters (#28432)
Parse leaf operands once and use token kinds to detect completed expressions, sharing continuation handling with normal expression parsing. Local 14-fixture benchmarks show ~2.4% less parse time with identifier hashes off and ~2.6% with hashes on; `typescript.js` uses ~4.8% fewer instructions. AI-assisted.
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@@ -1402,11 +1402,9 @@ impl<'a, C: Config> ParserImpl<'a, C> {
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let lhs = if kind == Kind::Ident {
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// Identifiers cannot start a unary or prefix-update expression. Parse their
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// suffixes directly, keeping pure annotations inside the postfix update.
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let lhs = self.with_pure_comments(|p| {
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let primary = p.parse_identifier_expression();
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p.parse_lhs_expression_rest(lhs_start, primary)
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});
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self.parse_postfix_update_expression(lhs_start, lhs)
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let pure_comments = self.lexer.trivia_builder.previous_token_pure_comments();
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let primary = self.parse_identifier_expression();
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self.parse_primary_expression_rest(lhs_start, primary, pure_comments)
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} else if self.ctx.has_in() && kind == Kind::PrivateIdentifier {
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// [+In] PrivateIdentifier in ShiftExpression[?Yield, ?Await]
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self.parse_private_in_expression(lhs_start, lhs_precedence)
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@@ -1416,30 +1414,10 @@ impl<'a, C: Config> ParserImpl<'a, C> {
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{
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self.parse_unary_expression_or_higher(lhs_start)
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} else {
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// Most operands start with a primary expression. Skip unary/update dispatch, and
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// only enter member/call parsing when the following token can extend the primary.
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// Most operands start with a primary expression. Skip unary/update dispatch.
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let pure_comments = self.lexer.trivia_builder.previous_token_pure_comments();
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let primary = self.parse_primary_expression();
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let mut lhs = if matches!(
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self.cur_kind(),
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Kind::Dot
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| Kind::LBrack
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| Kind::LParen
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| Kind::QuestionDot
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| Kind::NoSubstitutionTemplate
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| Kind::TemplateHead
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| Kind::Bang
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| Kind::LAngle
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| Kind::ShiftLeft
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) {
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self.parse_lhs_expression_rest(lhs_start, primary)
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} else {
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primary
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};
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if let Some(comments) = pure_comments {
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self.apply_pure_comments_to_call(comments, &mut lhs);
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}
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self.parse_postfix_update_expression(lhs_start, lhs)
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self.parse_primary_expression_rest(lhs_start, primary, pure_comments)
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};
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if kind_to_precedence(self.cur_kind()).is_none() {
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@@ -1448,6 +1426,36 @@ impl<'a, C: Config> ParserImpl<'a, C> {
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self.parse_binary_expression_rest(lhs_start, lhs, lhs_parenthesized, lhs_precedence)
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}
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#[expect(clippy::inline_always)]
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#[inline(always)]
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fn parse_primary_expression_rest(
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&mut self,
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start: u32,
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primary: Expression<'a>,
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pure_comments: Option<(u32, NonZeroU32)>,
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) -> Expression<'a> {
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let mut lhs = if matches!(
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self.cur_kind(),
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Kind::Dot
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| Kind::LBrack
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| Kind::LParen
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| Kind::QuestionDot
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| Kind::NoSubstitutionTemplate
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| Kind::TemplateHead
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| Kind::Bang
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| Kind::LAngle
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| Kind::ShiftLeft
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) {
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self.parse_lhs_expression_rest(start, primary)
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} else {
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primary
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};
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if let Some(comments) = pure_comments {
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self.apply_pure_comments_to_call(comments, &mut lhs);
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}
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self.parse_postfix_update_expression(start, lhs)
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}
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/// Section 13.6 - 13.13 Binary Expression
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fn parse_binary_expression_rest(
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&mut self,
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@@ -1628,42 +1636,71 @@ impl<'a, C: Config> ParserImpl<'a, C> {
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) -> Expression<'a> {
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let no_side_effects_comments =
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self.lexer.trivia_builder.previous_token_no_side_effects_comments();
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// [+Yield] YieldExpression
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if self.is_yield_expression() {
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return self.parse_yield_expression();
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}
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// `() => {}`, `(x) => {}`
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if matches!(self.cur_kind(), Kind::LParen | Kind::LAngle | Kind::Async)
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&& let Some(mut arrow_expr) = self.try_parse_parenthesized_arrow_function_expression(
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allow_return_type_in_arrow_function,
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)
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{
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if let Some(comments) = no_side_effects_comments
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&& let Expression::ArrowFunctionExpression(func) = &mut arrow_expr
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{
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func.pure = true;
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self.lexer.trivia_builder.mark_no_side_effects_comments_applied(comments);
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}
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return arrow_expr;
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}
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// `async x => {}`
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if self.at(Kind::Async)
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&& let Some(mut arrow_expr) = self.try_parse_async_simple_arrow_function_expression(
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allow_return_type_in_arrow_function,
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)
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{
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if let Some(comments) = no_side_effects_comments
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&& let Expression::ArrowFunctionExpression(func) = &mut arrow_expr
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{
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func.pure = true;
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self.lexer.trivia_builder.mark_no_side_effects_comments_applied(comments);
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}
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return arrow_expr;
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}
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let start = self.cur_start();
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let lhs_parenthesized = self.at(Kind::LParen);
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let lhs = self.parse_binary_expression_or_higher(Precedence::Comma);
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let kind = self.cur_kind();
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let lhs = if matches!(kind, Kind::Ident | Kind::This) || kind.is_literal() {
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let pure_comments = self.lexer.trivia_builder.previous_token_pure_comments();
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let primary = match kind {
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Kind::Ident => self.parse_plain_identifier_expression(),
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Kind::This => self.parse_this_expression(),
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_ => self.parse_literal_expression(),
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};
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// The leaf is complete when the next token is an expression delimiter.
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if matches!(
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self.cur_kind(),
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Kind::Comma
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| Kind::RParen
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| Kind::RBrack
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| Kind::RCurly
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| Kind::Semicolon
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| Kind::Colon
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) {
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return primary;
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}
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let lhs = self.parse_primary_expression_rest(start, primary, pure_comments);
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if kind_to_precedence(self.cur_kind()).is_none() {
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lhs
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} else {
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self.parse_binary_expression_rest(start, lhs, false, Precedence::Comma)
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}
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} else {
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// [+Yield] YieldExpression
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if self.is_yield_expression() {
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return self.parse_yield_expression();
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}
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// `() => {}`, `(x) => {}`
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if matches!(self.cur_kind(), Kind::LParen | Kind::LAngle | Kind::Async)
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&& let Some(mut arrow_expr) = self
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.try_parse_parenthesized_arrow_function_expression(
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allow_return_type_in_arrow_function,
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)
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{
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if let Some(comments) = no_side_effects_comments
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&& let Expression::ArrowFunctionExpression(func) = &mut arrow_expr
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{
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func.pure = true;
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self.lexer.trivia_builder.mark_no_side_effects_comments_applied(comments);
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}
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return arrow_expr;
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}
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// `async x => {}`
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if self.at(Kind::Async)
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&& let Some(mut arrow_expr) = self.try_parse_async_simple_arrow_function_expression(
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allow_return_type_in_arrow_function,
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)
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{
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if let Some(comments) = no_side_effects_comments
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&& let Expression::ArrowFunctionExpression(func) = &mut arrow_expr
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{
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func.pure = true;
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self.lexer.trivia_builder.mark_no_side_effects_comments_applied(comments);
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}
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return arrow_expr;
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}
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self.parse_binary_expression_or_higher(Precedence::Comma)
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};
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let lhs_parenthesized_span = lhs_parenthesized.then(|| self.end_span(start));
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let kind = self.cur_kind();
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