Done in #6847 , but there is room for performance improvement.

We want to keep the code as simple as possible and process the current 2 loops in 1 loop for duplicates detection.

https://github.com/tc39/proposal-duplicate-named-capturing-groups
https://tc39.es/ecma262/#sec-mightbothparticipate

For now, /(?<a>.)(?<a>.)/ is invalid syntax, name a is duplicated.

With this change, we can use the same name if they are splitted by | and in the same Disjunction like /(?<a>.)|(?<a>.)/.

But it still not allowed in some cases like /(?<n>|(?<n>))/, /(?<n>(?<n>)|)/, /((?<n>)|(?<n>))(?<n>)/, etc...

You need to track nesting level and | to mange scope.

TODOs

• Update count capturing parens logic to allow duplicates in certain cases

  • oxc/crates/oxc_regular_expression/src/parser/pattern_parser/state.rs

    Line 60 in 1282221

    fn parse_capturing_groups<'a>(

  • No need to change parser main logic
• Update README
  • https://github.com/oxc-project/oxc/blob/aa7718ab7bf0544b21564658a919307022f8824a/crates/oxc_regular_expression/README.md
• Update local tests
  • https://github.com/oxc-project/oxc/blob/aa7718ab7bf0544b21564658a919307022f8824a/crates/oxc_regular_expression/src/body_parser/mod.rs
• Enable conformance tests

  • oxc/tasks/coverage/src/test262/mod.rs

    Lines 103 to 104 in aa7718a

    	// ES2025 https://github.com/tc39/proposal-duplicate-named-capturing-groups
    	"regexp-duplicate-named-groups",