Nope'n! Error Prone Checker

To satisfy the checker, a class must meet one of three criteria:

1. Be declared final.
2. Be declared abstract.
3. Be annotated with @Open from the com.jakewharton.nopen.annotation package.

Any class that is neither final nor abstract and lacks the @Open annotation will trigger an error: [Nopen] Classes should be explicitly marked final, abstract, or @Open.

import com.jakewharton.nopen.annotation.Open;

final class Foo {}          // Valid
abstract class Bar {}      // Valid
@Open class Baz {}         // Valid

class Bad {}               // Error: [Nopen] Classes should be explicitly marked final, abstract, or @Open

If you want to disable the Nopen check specifically for test compilation in a standard Java project, configure the compileTestJava task to set the severity to OFF.

import net.ltgt.gradle.errorprone.CheckSeverity

tasks.named("compileTestJava").configure {
  options.errorprone.check("Nopen", CheckSeverity.OFF)
}

In Android projects, you can disable the Nopen check for both testVariants and unitTestVariants by configuring their javaCompileProvider.

import net.ltgt.gradle.errorprone.CheckSeverity

android.testVariants.all { variant ->
  variant.javaCompileProvider.configure {
    options.errorprone.check("Nopen", CheckSeverity.OFF)
  }
}
android.unitTestVariants.all { variant ->
  variant.javaCompileProvider.configure {
    options.errorprone.check("Nopen", CheckSeverity.OFF)
  }
}

To use Nope'n!, add the annotations to your compileOnly configuration and the checker to your errorprone configuration using the net.ltgt.errorprone plugin.

dependencies {
  compileOnly 'com.jakewharton.nopen:nopen-annotations:1.0.1'
  errorprone 'com.jakewharton.nopen:nopen-checker:1.0.1'
}