Add recipe to remove unused constructor and method parameters

[iddeepak]

What’s changed?

I’ve added a new recipe class, RemoveUnusedParams, that automatically removes parameters from Java methods when they’re declared but never referenced in the method body. It still respects:

• @OverRide methods (both explicit and those detected across the codebase)
• Native methods
• Parameters with their own annotations (e.g. @Deprecated)
• Constructors, varargs, interfaces, and other edge cases

Alongside the main recipe, I’ve expanded the unit tests to cover:

• Basic removal of unused parameters
• Preservation of used, overridden, and annotated parameters
• Constructors with unused arguments
• Varargs methods
• Native declarations
• Interface methods (no change expected)

What’s your motivation?

Over time, code tends to accumulate unused parameters—leftovers from refactoring, changing requirements, or evolving APIs. They add noise, make signatures harder to read, and can confuse future maintainers. This recipe:

1. Keeps signatures lean, showing exactly what each method actually needs
2. Automates cleanup, reducing manual PR churn
3. Helps enforce consistency across a large codebase

Anything in particular you'd like reviewers to focus on?

• Override detection: Does the scan/visitor logic reliably catch all overridden methods?
• Edge-case coverage: Any real-world patterns (e.g. multi-parameter annotations, complex varargs, inner-class overrides) that might slip through?
• Performance: The recipe now uses a single JavaIsoVisitor pass—does it still scale on large projects?

Anyone you would like to review specifically?

• @Pankraz76

Have you considered any alternatives or workarounds?

• Keeping the original “shadow-stack” approach to detect name shadowing more precisely—but in practice it added complexity without significant benefit.
• Using a dedicated MethodMatcher or type-based override detection; this felt like overkill for a simple annotation check.

Any additional context

• This work is driven by feedback on Issue #559.
• All existing tests pass, and I’ve verified the new cases locally with mvn test.
• I’ve also run the IntelliJ auto-formatter to keep the style consistent.

Checklist

• I’ve added unit tests to cover both positive and negative cases
• I’ve read and applied the recipe conventions and best practices
• I’ve used the IntelliJ IDEA auto-formatter on affected files

[Pankraz76]

well done!

try polish.

[Pankraz76]

This one done:

• https://pmd.github.io/pmd/pmd_rules_java_bestpractices.html#unusedformalparameter

Do we cover generic assignment as well? Might be dedicated recipe, to give options.

• https://pmd.github.io/pmd/pmd_rules_java_bestpractices.html#unusedassignment

[github-actions]

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[iddeepak]

This one done:

• https://pmd.github.io/pmd/pmd_rules_java_bestpractices.html#unusedformalparameter

Do we cover generic assignment as well? Might be dedicated recipe, to give options.

• https://pmd.github.io/pmd/pmd_rules_java_bestpractices.html#unusedassignment

RemoveUnusedParams only handles unused parameters. Unused assignments would need their own recipe

[github-actions]

Some suggestions could not be made:

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[Pankraz76]

try avoid feature envy (& DRY) giving single point of truth (SPOT)

[Pankraz76]

new test case - cover constructor as well.

[github-actions]

Some suggestions could not be made:

• src/main/resources/META-INF/rewrite/examples.yml
  • lines 328-345
  • lines 660-659
  • lines 705-721
  • lines 1254-1273
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  • lines 2251-2250
  • lines 2337-2336
  • lines 2352-2364
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[Pankraz76]

last polish.

Done very well, could already merge.

[github-actions]

Some suggestions could not be made:

• src/main/resources/META-INF/rewrite/examples.yml
  • lines 328-345
  • lines 660-659
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  • lines 1254-1273
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  • lines 2251-2250
  • lines 2337-2336
  • lines 2352-2364
  • lines 2801-2800
  • lines 2820-2831

[timtebeek]

Thanks already! Couple fixes applied just now, and a few more hints added where more work is needed. Let me know if you'd like to continue this yourself.

[iddeepak]

Thanks already! Couple fixes applied just now, and a few more hints added where more work is needed. Let me know if you'd like to continue this yourself.

Thank you for the updates and guidance! I’m tied up with some other work as well, but I’ll tackle the remaining items as soon as I have some free time. Please feel free to continue in the meantime.

[iddeepak]

Hey @timtebeek, thanks for flagging those edge cases—avoidDirectConflict, avoidInheritedConflict, and cascadeRemoveUnusedArguments. I’ll revisit the pruning logic with those in mind. In the meantime, if you have any suggestions on how to handle them, Let me know your thoughts!
@Pankraz76

[Pankraz76]

you are really talented, keep pushing @iddeepak.

[github-actions]

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