UnusedMethod flags @JsonValue methods as unused (original) (raw)

We have a couple of private static nested classes and enums with @JsonValue methods, mostly in tests. The UnusedMethod bug pattern flags those as unused, unlike the @JsonCreator methods.

Steps to reproduce

JsonValueExample.java

import java.util.Locale; import com.fasterxml.jackson.annotation.JsonCreator; import com.fasterxml.jackson.annotation.JsonValue;

public class JsonValueExample { private JsonValueExample() {}

private enum FooBar { FOO, BAR;

@JsonValue
String value() {
  return name().toLowerCase(Locale.ROOT);
}

@JsonCreator
static FooBar of(String value) {
  return valueOf(value.toUpperCase(Locale.ROOT));
}

} }

curl -LO https://repo1.maven.org/maven2/com/google/errorprone/error_prone_core/2.13.1/error_prone_core-2.13.1-with-dependencies.jar
curl -LO https://repo1.maven.org/maven2/com/fasterxml/jackson/core/jackson-annotations/2.13.1/jackson-annotations-2.13.1.jar

javac \
  -J--add-exports=jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED \
  -J--add-exports=jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED \
  -J--add-exports=jdk.compiler/com.sun.tools.javac.main=ALL-UNNAMED \
  -J--add-exports=jdk.compiler/com.sun.tools.javac.model=ALL-UNNAMED \
  -J--add-exports=jdk.compiler/com.sun.tools.javac.parser=ALL-UNNAMED \
  -J--add-exports=jdk.compiler/com.sun.tools.javac.processing=ALL-UNNAMED \
  -J--add-exports=jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED \
  -J--add-exports=jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED \
  -J--add-opens=jdk.compiler/com.sun.tools.javac.code=ALL-UNNAMED \
  -J--add-opens=jdk.compiler/com.sun.tools.javac.comp=ALL-UNNAMED \
  -cp jackson-annotations-2.13.1.jar \
  -XDcompilePolicy=simple \
  -processorpath error_prone_core-2.13.1-with-dependencies.jar \
  '-Xplugin:ErrorProne -XepDisableAllChecks -Xep:UnusedMethod:ERROR' \
  JsonValueExample.java

JsonValueExample.java:13: error: [UnusedMethod] Method 'value' is never used.
    String value() {
           ^
    (see https://errorprone.info/bugpattern/UnusedMethod)
  Did you mean 'BAR'?
1 error

A potential solution would be adding com.fasterxml.jackson.annotation.JsonValue to exempted annotations similar to JsonCreator.

Let me know if that makes sense; I can create a PR, as well.