Hacktoberfest 2026: the issues maintainers tagged for October, open and beginner-friendly. Browse Hacktoberfest issues

Local variable names in inner class methods aren't fixed when they conflict with outer names

Open
#86 3 comments 0 reactions 0 assignees View on GitHub

Nobody has claimed this yet.

Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
35/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
java
Domain
compilers

Research direction

Start with the FernFlower-Patches/0037-Do-not-rebuild-variable-names-in-lambdas.patch context, then inspect VarNamesCollector.setNewOuterNames and getFreeName(). Compare the current behavior with the earlier naming behavior described in the issue. Done means conflicting local names in inner methods are handled correctly without breaking the nested-scope behavior.

Written by the indexing model from the issue text.

Description

This is due to https://github.com/MinecraftForge/ForgeFlower/blob/master/FernFlower-Patches/0037-Do-not-rebuild-variable-names-in-lambdas.patch

For background on what that code is doing (re: the patch message):
That allows the decompiler to fix variable names in a nested class or lambda expression which clashes with the name of an outer variable.

What's happening is it's checking the names for the current method against the variable names defined in the outer scope. That's why setNewOuterNames is passed to VarNamesCollector, then checked for in VarNamesCollector.getFreeName() - the outer names are compared against the names for the nested method.

What FernFlower's code originally did was append x to local variable names when conflicts came up - but now it doesn't do that because of that patch. Considering that's the only thing that method is actually doing I don't know what the patch is actually trying to fix. The commit which added the patch said it fixes #88, but there is no issue 88 yet.

This comes up relatively infrequently, and I guess never in MCP due to how LVT is handled, but it causes an issue with my usage. This quick and dirty fix is because of this issue - previous versions of FernFlower would rename the inner i variable to ix. https://github.com/PaperMC/Paper/blob/mappings/mojang/Spigot-Server-Patches/0266-Optimize-BlockPosition-helper-methods.patch#L113-L134

Dominant language
No language data
Stars
110
Forks
49
PR merge metrics
No merged PRs in 30d

Contributor guide

No contributing guide indexed for this repository

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

More from MinecraftForge/ForgeFlower

All issues in MinecraftForge/ForgeFlower

Similar issues

More Compilers issues

Get new issues in your inbox

A short digest of beginner-friendly GitHub issues.