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refactor(parser): remove token lookahead in type parsing #11241

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graphite-app merged 1 commit into from
May 23, 2025
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refactor(parser): remove token lookahead in type parsing #11241

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77 changes: 52 additions & 25 deletions crates/oxc_parser/src/ts/types.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -87,7 +87,13 @@ impl<'a> ParserImpl<'a> {
if self.at(Kind::LParen) && self.lookahead(Self::is_unambiguously_start_of_function_type) {
return true;
}
self.at(Kind::New) || (self.at(Kind::Abstract) && self.peek_at(Kind::New))
self.at(Kind::New)
|| (self.at(Kind::Abstract) && self.lookahead(Self::is_next_token_new_keyword))
}

fn is_next_token_new_keyword(&mut self) -> bool {
self.bump_any();
self.at(Kind::New)
}

fn is_unambiguously_start_of_function_type(&mut self) -> bool {
Expand Down Expand Up @@ -363,7 +369,7 @@ impl<'a> ParserImpl<'a> {
self.parse_literal_type_node(/* negative */ false)
}
Kind::Minus => {
if self.peek_kind().is_number() {
if self.lookahead(Self::is_next_token_number) {
self.parse_literal_type_node(/* negative */ true)
} else {
self.parse_type_reference()
Expand All @@ -378,10 +384,17 @@ impl<'a> ParserImpl<'a> {
let span = self.start_span();
self.bump_any(); // bump `this`
let this_type = self.ast.ts_this_type(self.end_span(span));
if self.peek_at(Kind::Is) && !self.peek_token().is_on_new_line() {
return self.parse_this_type_predicate(this_type);
// TODO: rewind should not be necessary here, but it causes a regression in the
// conformance test suite otherwise
let checkpoint = self.checkpoint();
self.bump_any();
let kind = self.cur_kind();
self.rewind(checkpoint);
if kind == Kind::Is && !self.cur_token().is_on_new_line() {
self.parse_this_type_predicate(this_type)
} else {
TSType::TSThisType(self.alloc(this_type))
}
TSType::TSThisType(self.alloc(this_type))
}
Kind::Typeof => {
self.parse_type_query()
Expand All @@ -397,8 +410,7 @@ impl<'a> ParserImpl<'a> {
Kind::LParen => self.parse_parenthesized_type(),
Kind::Import => TSType::TSImportType(self.parse_ts_import_type()),
Kind::Asserts => {
let peek_token = self.peek_token();
if peek_token.kind().is_identifier_name() && !peek_token.is_on_new_line() {
if self.lookahead(Self::is_next_token_identifier_or_keyword_on_same_line) {
self.parse_asserts_type_predicate()
} else {
self.parse_type_reference()
Expand All @@ -409,6 +421,16 @@ impl<'a> ParserImpl<'a> {
}
}

fn is_next_token_identifier_or_keyword_on_same_line(&mut self) -> bool {
self.bump_any();
self.cur_kind().is_identifier_name() && !self.cur_token().is_on_new_line()
}

fn is_next_token_number(&mut self) -> bool {
self.bump_any();
self.cur_kind().is_number()
}

fn parse_keyword_and_no_dot(&mut self) -> TSType<'a> {
let span = self.start_span();
let ty = match self.cur_kind() {
Expand Down Expand Up @@ -502,7 +524,7 @@ impl<'a> ParserImpl<'a> {
| Kind::NoSubstitutionTemplate
| Kind::TemplateHead => true,
Kind::Function => !in_start_of_parameter,
Kind::Minus => !in_start_of_parameter && self.peek_kind().is_number(),
Kind::Minus => !in_start_of_parameter && self.lookahead(Self::is_next_token_number),
Kind::LParen => {
!in_start_of_parameter
&& self.lookahead(Self::is_start_of_parenthesized_or_function_type)
Expand All @@ -512,23 +534,20 @@ impl<'a> ParserImpl<'a> {
}

fn is_start_of_mapped_type(&mut self) -> bool {
if !self.at(Kind::LCurly) {
return false;
}

if self.peek_at(Kind::Plus) || self.peek_at(Kind::Minus) {
return self.nth_at(2, Kind::Readonly);
self.bump_any();
if self.at(Kind::Plus) || self.at(Kind::Minus) {
self.bump_any();
return self.at(Kind::Readonly);
}

let mut offset = 1;
self.bump(Kind::Readonly);

if self.nth_at(offset, Kind::Readonly) {
offset += 1;
if !self.eat(Kind::LBrack) && self.cur_kind().is_identifier_name() {
return false;
}

self.nth_at(offset, Kind::LBrack)
&& self.nth_kind(offset + 1).is_identifier_name()
&& self.nth_at(offset + 2, Kind::In)
self.bump_any();
self.at(Kind::In)
}

fn next_token_is_start_of_type(&mut self) -> bool {
Expand Down Expand Up @@ -903,7 +922,7 @@ impl<'a> ParserImpl<'a> {
if self.at(Kind::Colon) {
return true;
}
self.at(Kind::Question) && self.peek_at(Kind::Colon)
self.eat(Kind::Question) && self.at(Kind::Colon)
}

fn parse_tuple_element_type(&mut self) -> TSTupleElement<'a> {
Expand Down Expand Up @@ -1078,7 +1097,12 @@ impl<'a> ParserImpl<'a> {
}

pub(crate) fn is_next_at_type_member_name(&mut self) -> bool {
self.peek_kind().is_literal_property_name() || self.peek_at(Kind::LBrack)
self.lookahead(Self::is_next_at_type_member_name_worker)
}

fn is_next_at_type_member_name_worker(&mut self) -> bool {
self.bump_any();
self.cur_kind().is_literal_property_name() || self.at(Kind::LBrack)
}

pub(crate) fn parse_ts_call_signature_member(&mut self) -> TSSignature<'a> {
Expand Down Expand Up @@ -1356,10 +1380,13 @@ impl<'a> ParserImpl<'a> {
| Kind::New
| Kind::Slash
| Kind::SlashEq => true,
Kind::Import => {
matches!(self.peek_kind(), Kind::LParen | Kind::LAngle | Kind::Dot)
}
Kind::Import => self.lookahead(Self::is_next_token_paren_less_than_or_dot),
_ => false,
}
}

fn is_next_token_paren_less_than_or_dot(&mut self) -> bool {
self.bump_any();
matches!(self.cur_kind(), Kind::LParen | Kind::LAngle | Kind::Dot)
}
}
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