RemoveUnusedParams #560

iddeepak · 2025-05-16T04:14:22Z

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:

Keeps signatures lean, showing exactly what each method actually needs
Automates cleanup, reducing manual PR churn
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.

src/main/java/org/openrewrite/staticanalysis/RemoveUnusedParams.java

Pankraz76 · 2025-05-16T07:57:38Z

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

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src/main/java/org/openrewrite/staticanalysis/RemoveUnusedParams.java

src/test/java/org/openrewrite/staticanalysis/RemoveUnusedParamsTest.java

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src/test/java/org/openrewrite/staticanalysis/RemoveUnusedParamsTest.java

iddeepak · 2025-05-16T15:25:35Z

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

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src/main/java/org/openrewrite/staticanalysis/RemoveUnusedParams.java

…s.java Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Pankraz76

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

src/main/java/org/openrewrite/staticanalysis/RemoveUnusedParams.java

Pankraz76

new test case - cover constructor as well.

src/test/java/org/openrewrite/staticanalysis/RemoveUnusedParamsTest.java

Updated review comments Updated review comments Updated review comments Updated review comments Updated review comments Updated review comments Updated review comments Updated review comments Updated review comments Updated review comments Updated review comments Updated review comments Updated review comments Updated review comments Updated review comments Updated review comments Updated review comments

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src/main/java/org/openrewrite/staticanalysis/RemoveUnusedParams.java

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Pankraz76

last polish.

Done very well, could already merge.

src/main/java/org/openrewrite/staticanalysis/RemoveUnusedParams.java

src/test/java/org/openrewrite/staticanalysis/RemoveUnusedParamsTest.java

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src/main/java/org/openrewrite/staticanalysis/RemoveUnusedParams.java

Pankraz76

uncle bob would be proud.

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src/main/java/org/openrewrite/staticanalysis/RemoveUnusedParams.java

Pankraz76 · 2025-05-19T06:47:59Z

this could be follow up:

iddeepak · 2025-05-19T15:12:28Z

this could be follow up:

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

UnusedAssignment apache/maven#2350

@Pankraz76 Thanks! I’ve opened Issue #564 to track adding the UnusedAssignment recipe. Please feel free to drop any additional examples or feedback over there!

timtebeek · 2025-05-19T17:21:51Z

Thanks both! I'm not likely to get to a review this week with travel ahead, but perhaps @MBoegers can have a look while I'm out.

timtebeek

A quick first round of review; great that you worked out you need a scanning recipe already; My comments are mostly to make better use of utilities and conventions we have in the project.

src/main/java/org/openrewrite/staticanalysis/RemoveUnusedParams.java

timtebeek · 2025-05-19T17:24:05Z

src/main/java/org/openrewrite/staticanalysis/RemoveUnusedParams.java

+    private J.MethodDeclaration collectOverrideSignature(final J.MethodDeclaration m, final Accumulator acc) {
+        m.getLeadingAnnotations().stream()
+                .map(J.Annotation::getSimpleName)
+                .filter(OVERRIDE_ANNOTATION::equals)
+                .findAny()
+                .ifPresent(annotationName -> acc.add(buildSignature(m)));
+        return m;
+    }


Rather than look for an override annotation, we have a method called isOverride on the type that should be used here instead.

timtebeek · 2025-05-19T17:27:54Z

src/main/java/org/openrewrite/staticanalysis/RemoveUnusedParams.java

+    private boolean isShadowed(final String name, final Deque<Set<String>> shadowStack) {
+        return shadowStack.stream().anyMatch(scope -> scope.contains(name));
+    }
+
+    private boolean isDeclaredAsParameter(final String name, final J.MethodDeclaration m) {
+        return m.getParameters().stream()
+                .filter(p -> p instanceof J.VariableDeclarations)
+                .flatMap(p -> ((J.VariableDeclarations) p).getVariables().stream())
+                .anyMatch(v -> v.getSimpleName().equals(name));
+    }
+
+    private List<Statement> filterUnusedParameters(final J.MethodDeclaration m, final Set<String> usedParams) {
+        return m.getParameters().stream()
+                .flatMap(param -> param instanceof J.VariableDeclarations ?
+                        filterDeclaration((J.VariableDeclarations) param, usedParams)
+                        : Stream.of(param))
+                .collect(Collectors.toList());
+    }
+
+    private Stream<Statement> filterDeclaration(final J.VariableDeclarations decl, final Set<String> usedParams) {
+        return Optional.of(decl)
+                .filter(d -> !d.getLeadingAnnotations().isEmpty())
+                .map(d -> Stream.<Statement>of(d))
+                .orElseGet(() -> pruneByUsage(decl, usedParams));
+    }
+
+    private Stream<Statement> pruneByUsage(final J.VariableDeclarations decl, final Set<String> usedParams) {
+        return Optional.of(collectUsedParameters(decl, usedParams))
+                .filter(kept -> !kept.isEmpty())
+                .map(kept -> Stream.<Statement>of(decl.withVariables(kept)))
+                .orElseGet(Stream::empty);
+    }
+
+    private List<J.VariableDeclarations.NamedVariable> collectUsedParameters(final J.VariableDeclarations decl, final Set<String> usedParams) {
+        return decl.getVariables().stream()
+                .filter(v -> usedParams.contains(v.getSimpleName()))
+                .collect(Collectors.toList());
+    }


In general we try to avoid the streams API for as much as possible, especially when applied to every LST element of a particular type, as it leads to poor performance at scale with a lot of object allocations. Keep in kind that we're targeting Java 8 still, so any performance improvements in newer Java versions do not automatically apply.

Understood, I replaced those streams with plain loops

might consider rule for this, with checkstyle custom imports. This is never ending story other way.

Sorry forgot about stream limitation. Its random impl. detail, at least functional method scope can be obtained.

This case could be new a migration recipe as well.

In both ways: giving lambda from list and backwards like seen here.

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github-actions · 2025-05-19T19:18:42Z

src/main/java/org/openrewrite/staticanalysis/RemoveUnusedParams.java

+import java.time.Duration;
+import java.util.ArrayDeque;


Suggested change

import java.time.Duration;

import java.util.ArrayDeque;

import java.util.ArrayDeque;

github-actions · 2025-05-19T19:18:42Z

src/main/java/org/openrewrite/staticanalysis/RemoveUnusedParams.java

+        return m.getBody() != null
+                && m.getMethodType() != null
+                && !m.hasModifier(J.Modifier.Type.Native)
+                && m.getLeadingAnnotations().isEmpty()
+                && !acc.contains(buildSignature(m));
+    }
+


Suggested change

return m.getBody() != null

&& m.getMethodType() != null

&& !m.hasModifier(J.Modifier.Type.Native)

&& m.getLeadingAnnotations().isEmpty()

&& !acc.contains(buildSignature(m));

}

return m.getBody() != null &&

m.getMethodType() != null &&

!m.hasModifier(J.Modifier.Type.Native) &&

m.getLeadingAnnotations().isEmpty() &&

!acc.contains(buildSignature(m));

return m.getSimpleName() + "#" +

m.getMethodType().getParameterTypes().stream()

timtebeek · 2025-05-19T19:19:36Z

src/main/java/org/openrewrite/staticanalysis/RemoveUnusedParams.java

+        return m.getSimpleName() + "#"
+                + m.getMethodType().getParameterTypes().stream()
+                .map(Object::toString)
+                .collect(Collectors.joining(","));


Please use MethodMatcher.methodPattern here instead of composing this yourself.

Add RemoveUnusedParams recipe

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Parameter 'request' is never used apache/maven#2338

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[POC] rewrite-maven-plugin: Introduce OpenRewrite by Moderne apache/maven#2322

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Merge branch 'main' into feature/RemoveUnusedParams

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RemoveUnusedAssignments #564

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RemoveUnusedParams #560

RemoveUnusedParams #560

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	import java.time.Duration;
	import java.util.ArrayDeque;
	import java.util.ArrayDeque;

RemoveUnusedParams #560

Are you sure you want to change the base?

RemoveUnusedParams #560

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iddeepak commented May 16, 2025

What’s changed?

What’s your motivation?

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

Anyone you would like to review specifically?

Have you considered any alternatives or workarounds?

Any additional context

Checklist

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