[mathiasrw]

Closes #799

Stacked on #805.

Change

• A named group is a variable in --js code, with rr_ in front: rr_year for (?<year>…). rr_year_ has a space at the end, like the other variables. The prefix keeps them apart from the other variables, so no name of a group can clash. (This PR used _ as the prefix. Access named groups from --js code to close #825 #832 changed it to rr_.)

> echo -n '2024-05' | rexreplace '(?<year>\d{4})-(?<month>\d\d)' 'rr_month + "/" + rr_year' --js
05/2024

• A named group that took no part in the match is undefined.
• When the code uses a named group, it runs once per match, like for $0 and $1.
• Fix: with a named group in the pattern, the position of the match became an extra group variable ($3 was 0 with two groups). Now only the match and the groups get a variable, like --output-match already did.

Tests

yarn test-ci passes: the demo on Node and Bun, and 1019 Bun tests. test/fix/799.test.js is new.