mozilla/rhino

Write an OpenRewrite rule to migrate to Rhino 2.0

Open

#2,363 opened on Apr 12, 2026

View on GitHub
 (2 comments) (0 reactions) (0 assignees)JavaScript (812 forks)batch import
good first issue

Repository metrics

Stars
 (3,728 stars)
PR merge metrics
 (Avg merge 6d 16h) (15 merged PRs in 30d)

Description

With the current work on the "master" branch we have finally reached the point where existing Rhino code will need to change, specifically to use the new VarScope class to represent the scope in every call instead of Scriptable. This is a big change, although one that doesn't require a ton of thinking!

OpenRewrite is a great framework well-suited to applying these kinds of changes automatically -- we recently used it in this project to convert from Junit 4 to 5, for example. It accomplished this deterministic task with much less drama and prompting and a lot less money spent than trying to solve that same problem using your favorite LLM.

Contributor guide

Research direction
Study OpenRewrite recipes for automated code migration. Identify all places in Rhino codebase where Scriptable is used as scope parameter and need to be replaced with VarScope. Create a recipe using OpenRewrite's refaster template or Java template to perform the transformation. Validate with tests.
Tech stack
javajavascript
Domain
backend
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
JavaOpenRewrite
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20