Annotation processor for switch exhaustiveness checks in Java

This annotation processor allows you to check, that you cover all switch-cases for Enum switch statements.

Switch exhaustiveness has already been implemented in https://openjdk.org/jeps/361. However, there are a few "drawbacks" of it:

1. You need to use Java 14, whereas this annotation processor allows you to have Java 8.
2. JEP 361 is implemented for switch expressions (which is totally fine, though), whereas this annotation processor allows you to have switch statements instead of.

How to use in gradle

1. Include to your project and enable SwitchExhaustiveCheckerProcessor annotation processor. For example, for gradle:

repositories {
    // ...
    mavenCentral()
    // ...
}

dependencies {
    // ....
    compileOnly 'ru.hixon:switch-exhaustiveness-checker:1.2'
    annotationProcessor 'ru.hixon:switch-exhaustiveness-checker:1.2'
    // ...
}

2. Put annotation ru.hixon.switchexhaustivenesschecker.SwitchExhaustive to needed constructors, methods and classes:

import ru.hixon.switchexhaustivenesschecker.SwitchExhaustive;

@SwitchExhaustive
public class ClassWithEnum2ConstructorBad {

    public enum Enum2 {
        EnumVal1,
        EnumVal2
    }

    public void foo(Enum2 enum2) {
        switch (enum2) {
            case EnumVal1:
                break;
        }
    }
}

3. You should see an error, like this:

src/main/java/ClassWithEnum2ConstructorBad.java:11: error: Switch branches: [EnumVal2] in class: [ClassWithEnum2ConstructorBad], method: [foo] are not covered
    public void foo(Enum2 enum2) {

How to use in maven

1. Add optional dependency to your dependencies:

<dependencies>
    <dependency>
        <groupId>ru.hixon</groupId>
        <artifactId>switch-exhaustiveness-checker</artifactId>
        <version>1.2</version>
        <optional>true</optional>
    </dependency>
</dependencies>

2. Enable the annotation processor:

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.10.1</version>
            <configuration>
                <annotationProcessors>
                    <annotationProcessor>
                        ru.hixon.switchexhaustivenesschecker.SwitchExhaustiveCheckerProcessor
                    </annotationProcessor>
                </annotationProcessors>
            </configuration>
        </plugin>
    </plugins>
</build>

If you use Lombok, you need explicitly enable both annotation processors:

<build>
	<plugins>
		<plugin>
			<groupId>org.apache.maven.plugins</groupId>
			<artifactId>maven-compiler-plugin</artifactId>
			<version>3.10.1</version>
			<configuration>
				<annotationProcessorPaths>
					<path>
						<groupId>ru.hixon</groupId>
						<artifactId>switch-exhaustiveness-checker</artifactId>
						<version>1.2</version>
					</path>
					<path>
						<groupId>org.projectlombok</groupId>
						<artifactId>lombok</artifactId>
						<version>1.18.24</version>
					</path>
				</annotationProcessorPaths>
			</configuration>
		</plugin>
	</plugins>
</build>

3. Put annotation ru.hixon.switchexhaustivenesschecker.SwitchExhaustive to needed constructors, methods and classes:

import ru.hixon.switchexhaustivenesschecker.SwitchExhaustive;

@SwitchExhaustive
public class ClassWithEnum2ConstructorBad {

    public enum Enum2 {
        EnumVal1,
        EnumVal2
    }

    public ClassWithEnum2ConstructorBad(Enum2 enum2) {
        switch (enum2) {
            case EnumVal1:
                break;
        }
    }
}

How it works

An annotation processor SwitchExhaustiveCheckerProcessor processes all classes and methods, which are annotated by @SwitchExhaustive. The processor finds all switch statements, and after that verifies, that all cases for Enum-constants are covered.

The annotation processor is executed as one of compilation step. Hence you can be sure, that all cases for Enums are covered, if compilation process of your program has completed successfully.

How to build and upload a new version to maven central

1. Specify correct credentials in gradle.properties (you can find it in the root folder of project).
2. Execute ./gradlew clean build uploadArchives
3. Release the artifact - https://central.sonatype.org/publish/release/.

Credits

1. https://github.com/svbrunov - for helping with implementation of the processor.
2. https://github.com/skinny85/jilt - for an annotation processor example.