Add compile-time null safety

buildSrc/build.gradle.kts

@@ -6,6 +6,7 @@ repositories {
 
 dependencies {
     implementation("com.github.spotbugs.snom:spotbugs-gradle-plugin:5.2.5")
+    implementation("org.checkerframework:checkerframework-gradle-plugin:0.6.61")
 }
 
 gradlePlugin {
@@ -26,5 +27,9 @@ gradlePlugin {
             id = "com.navercorp.fixturemonkey.gradle.plugin.object-farm-maven-publish-conventions"
             implementationClass = "com.navercorp.fixturemonkey.gradle.plugin.ObjectFarmMavenPublishConventionsPlugin"
         }
+        register("checkerFrameworkConventionsPlugin") {
+            id = "com.navercorp.fixturemonkey.gradle.plugin.checker-framework-conventions"
+            implementationClass = "com.navercorp.fixturemonkey.gradle.plugin.CheckerFrameworkConventionsPlugin"
+        }
     }
 }

buildSrc/src/main/kotlin/com/navercorp/fixturemonkey/gradle/plugin/CheckerFrameworkConventionsPlugin.kt

@@ -0,0 +1,39 @@
+/*
+ * Fixture Monkey
+ *
+ * Copyright (c) 2021-present NAVER Corp.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.navercorp.fixturemonkey.gradle.plugin
+
+import org.checkerframework.gradle.plugin.CheckerFrameworkExtension
+import org.gradle.api.Plugin
+import org.gradle.api.Project
+import org.gradle.kotlin.dsl.getByType
+
+class CheckerFrameworkConventionsPlugin : Plugin<Project> {
+    override fun apply(project: Project) {
+        project.plugins.apply("org.checkerframework")
+
+        project.extensions.getByType<CheckerFrameworkExtension>().apply {
+            checkers = listOf("org.checkerframework.checker.nullness.NullnessChecker")
+            extraJavacArgs = listOf(
+                "-AsuppressWarnings=initialization,method.invocation,type.arguments"
+            )
+            excludeTests = true
+        }
+    }
+}
+

buildSrc/src/main/kotlin/com/navercorp/fixturemonkey/gradle/plugin/JavaConventionsPlugin.kt

@@ -23,6 +23,7 @@ import org.gradle.api.Project
 
 class JavaConventionsPlugin : Plugin<Project> {
     override fun apply(project: Project) {
+        CheckerFrameworkConventionsPlugin().apply(project)
         CheckstyleConventionsPlugin().apply(project)
         SpotbugsConventionsPlugin().apply(project)
         JacocoConventionsPlugin().apply(project)

fixture-monkey-api/build.gradle.kts

@@ -19,6 +19,9 @@ multiReleaseVersions.forEach { releaseVersion ->
                 .replaceFirstChar { it.lowercase() }
 
             configuration.extendsFrom(configurations.getByName(defaultVersionConfigurationName))
+
+            val checkerFrameworkExtension = project.extensions.findByType<org.checkerframework.gradle.plugin.CheckerFrameworkExtension>()
+            checkerFrameworkExtension?.skipCheckerFramework = true
         }
 }
 

fixture-monkey-api/src/main/java/com/navercorp/fixturemonkey/api/arbitrary/ContainerCombinableArbitrary.java

@@ -48,6 +48,7 @@ final class ContainerCombinableArbitrary<T> implements CombinableArbitrary<T> {
 	}
 
 	@Override
+	@SuppressWarnings("type.arguments.not.inferred")
 	public T combined() {
 		List<Object> combinedList = combinableArbitraryList.stream()
 			.map(CombinableArbitrary::combined)
@@ -57,6 +58,7 @@ public T combined() {
 	}
 
 	@Override
+	@SuppressWarnings({"return"})
 	public Object rawValue() {
 		List<Object> rawValues = combinableArbitraryList.stream()
 			.map(CombinableArbitrary::rawValue)
@@ -85,6 +87,7 @@ public boolean fixed() {
 	}
 
 	@Override
+	@SuppressWarnings("argument")
 	public CombinableArbitrary<T> unique() {
 		List<CombinableArbitrary<?>> uniqueCombinableArbitraryList = this.combinableArbitraryList.stream()
 			.map(arbitrary -> arbitrary.filter(it -> {

fixture-monkey-api/src/main/java/com/navercorp/fixturemonkey/api/arbitrary/FilteredCombinableArbitrary.java

@@ -123,7 +123,7 @@ public T combined() {
 		throw newRetryableFilterMissException(lastException);
 	}
 
-	@SuppressWarnings("unchecked")
+	@SuppressWarnings({"unchecked", "override.return", "argument"})
 	@Override
 	public T rawValue() {
 		T returned;
@@ -205,6 +205,7 @@ public CombinableArbitrary<T> unique() {
 		return combinableArbitrary.unique();
 	}
 
+	@SuppressWarnings("argument")
 	private RetryableFilterMissException newRetryableFilterMissException(@Nullable Throwable throwable) {
 		if (!(throwable instanceof RetryableFilterMissException)) {
 			return new RetryableFilterMissException(throwable);

fixture-monkey-api/src/main/java/com/navercorp/fixturemonkey/api/arbitrary/FixedCombinableArbitrary.java

@@ -22,6 +22,7 @@
 
 import org.apiguardian.api.API;
 import org.apiguardian.api.API.Status;
+import org.jspecify.annotations.Nullable;
 
 /**
  * It would generate a fixed value {@code object}.
@@ -40,6 +41,7 @@ public T combined() {
 	}
 
 	@Override
+	@SuppressWarnings("override.return")
 	public T rawValue() {
 		return object;
 	}
@@ -54,7 +56,7 @@ public boolean fixed() {
 	}
 
 	@Override
-	public boolean equals(Object obj) {
+	public boolean equals(@Nullable Object obj) {
 		if (this == obj) {
 			return true;
 		}

fixture-monkey-api/src/main/java/com/navercorp/fixturemonkey/api/arbitrary/LazyCombinableArbitrary.java

@@ -43,6 +43,7 @@ public T combined() {
 	}
 
 	@Override
+	@SuppressWarnings("return")
 	public Object rawValue() {
 		Object rawValue = introspected.getValue();
 		introspected.clear();

fixture-monkey-api/src/main/java/com/navercorp/fixturemonkey/api/arbitrary/MappedCombinableArbitrary.java

@@ -43,9 +43,9 @@ public U combined() {
 		return mapper.apply(combinableArbitrary.combined());
 	}
 
-	@SuppressWarnings("unchecked")
+	@SuppressWarnings({"unchecked", "return"})
 	@Override
-	public U rawValue() {
+	public Object rawValue() {
 		try {
 			return mapper.apply((T)combinableArbitrary.rawValue());
 		} catch (ClassCastException ex) {

fixture-monkey-api/src/main/java/com/navercorp/fixturemonkey/api/arbitrary/MonkeyStringArbitrary.java

@@ -32,6 +32,8 @@
 
 import org.apiguardian.api.API;
 import org.apiguardian.api.API.Status;
+import org.jspecify.annotations.NonNull;
+import org.jspecify.annotations.Nullable;
 
 import net.jqwik.api.Arbitrary;
 import net.jqwik.api.EdgeCases;
@@ -57,16 +59,17 @@ public final class MonkeyStringArbitrary implements StringArbitrary {
 	private CharacterArbitrary characterArbitrary = new DefaultCharacterArbitrary();
 
 	private int minLength = 0;
-	private Integer maxLength = null;
+	private @Nullable Integer maxLength = null;
 	private Predicate<Character> filter = c -> true;
+	@SuppressWarnings("assignment")
 	private RandomDistribution lengthDistribution = null;
 	private double repeatChars = 0.0;
 
 	@Override
 	public RandomGenerator<String> generator(int genSize) {
 		long maxUniqueChars = characterArbitrary
 			.exhaustive(maxLength())
-			.map(ExhaustiveGenerator::maxCount)
+			.<@NonNull Long>map(ExhaustiveGenerator::maxCount)
 			.orElse((long)maxLength());
 		return RandomGenerators.strings(
 			randomCharacterGenerator(),
@@ -82,6 +85,7 @@ public RandomGenerator<String> generator(int genSize, boolean withEdgeCases) {
 		return this.generator(genSize);
 	}
 
+	@SuppressWarnings("argument")
 	private int maxLength() {
 		return RandomGenerators.collectionMaxSize(minLength, maxLength);
 	}
@@ -250,7 +254,7 @@ public StringArbitrary excludeChars(char... charsToExclude) {
 	}
 
 	@Override
-	public boolean equals(Object obj) {
+	public boolean equals(@Nullable Object obj) {
 		if (this == obj) {
 			return true;
 		}

fixture-monkey-api/src/main/java/com/navercorp/fixturemonkey/api/arbitrary/NullInjectCombinableArbitrary.java

@@ -39,7 +39,7 @@ final class NullInjectCombinableArbitrary<T> implements CombinableArbitrary<T> {
 		this.nullProbability = nullProbability;
 	}
 
-	@SuppressWarnings("unchecked")
+	@SuppressWarnings({"unchecked", "argument"})
 	@Override
 	public T combined() {
 		T combined = combinableArbitrary.combined();
@@ -50,6 +50,7 @@ public T combined() {
 		return (T)injectNull(combined);
 	}
 
+	@SuppressWarnings("return")
 	@Override
 	public Object rawValue() {
 		Object rawValue = combinableArbitrary.rawValue();

fixture-monkey-api/src/main/java/com/navercorp/fixturemonkey/api/arbitrary/ObjectCombinableArbitrary.java

@@ -43,6 +43,7 @@ final class ObjectCombinableArbitrary<T> implements CombinableArbitrary<T> {
 		this.combinator = combinator;
 	}
 
+	@SuppressWarnings("argument")
 	@Override
 	public T combined() {
 		Map<ArbitraryProperty, Object> combinedPropertyValuesByArbitraryProperty = new HashMap<>();
@@ -54,6 +55,7 @@ public T combined() {
 		return combinator.apply(combinedPropertyValuesByArbitraryProperty);
 	}
 
+	@SuppressWarnings({"return", "argument"})
 	@Override
 	public Object rawValue() {
 		Map<ArbitraryProperty, Object> rawPropertyValuesByArbitraryProperty = new HashMap<>();

fixture-monkey-api/src/main/java/com/navercorp/fixturemonkey/api/arbitrary/StringCombinableArbitraryDelegator.java

@@ -68,6 +68,7 @@ public StringCombinableArbitrary filter(int tries, Predicate<String> predicate)
 	}
 
 	@Override
+	@SuppressWarnings("argument")
 	public StringCombinableArbitrary filterCharacter(int tries, Predicate<Character> predicate) {
 		return this.filter(tries, it -> it.chars().mapToObj(Character.class::cast).allMatch(predicate));
 	}

fixture-monkey-api/src/main/java/com/navercorp/fixturemonkey/api/arbitrary/UniqueCombinableArbitrary.java

@@ -40,6 +40,7 @@ final class UniqueCombinableArbitrary<T> implements CombinableArbitrary<T> {
 	}
 
 	@Override
+	@SuppressWarnings("argument")
 	public T combined() {
 		return combinableArbitrary.filter(
 			it -> {
@@ -53,6 +54,7 @@ public T combined() {
 	}
 
 	@Override
+	@SuppressWarnings("argument")
 	public Object rawValue() {
 		return combinableArbitrary.filter(
 			it -> {

fixture-monkey-api/src/main/java/com/navercorp/fixturemonkey/api/container/ConcurrentLruCache.java

@@ -24,6 +24,7 @@
 
 import org.apiguardian.api.API;
 import org.apiguardian.api.API.Status;
+import org.jspecify.annotations.Nullable;
 
 /**
  * It is the Concurrent Least Recently Used cache.
@@ -32,8 +33,8 @@
  * @param <K> key of the cache
  * @param <V> value of the cache
  */
-@SuppressWarnings("NullableProblems")
 @API(since = "0.5.10", status = Status.MAINTAINED)
+@SuppressWarnings({"contracts", "override", "return"})
 public final class ConcurrentLruCache<K, V> implements Map<K, V> {
 	private final Map<K, V> lruCache;
 
@@ -62,7 +63,7 @@ public boolean containsValue(Object value) {
 	}
 
 	@Override
-	public V get(Object key) {
+	public @Nullable V get(Object key) {
 		return lruCache.get(key);
 	}
 

fixture-monkey-api/src/main/java/com/navercorp/fixturemonkey/api/container/DefaultDecomposedContainerValueFactory.java

@@ -50,6 +50,7 @@ public DefaultDecomposedContainerValueFactory(
 	}
 
 	@Override
+	@SuppressWarnings("argument")
 	public DecomposableJavaContainer from(Object container) {
 		Class<?> actualType = container.getClass();
 

fixture-monkey-api/src/main/java/com/navercorp/fixturemonkey/api/context/MonkeyContext.java

@@ -25,6 +25,7 @@
 
 import org.apiguardian.api.API;
 import org.apiguardian.api.API.Status;
+import org.jspecify.annotations.Nullable;
 
 import com.navercorp.fixturemonkey.api.ObjectBuilder;
 import com.navercorp.fixturemonkey.api.arbitrary.CombinableArbitrary;
@@ -69,7 +70,7 @@ public static MonkeyContextBuilder builder(FixtureMonkeyOptions fixtureMonkeyOpt
 		return new MonkeyContextBuilder(fixtureMonkeyOptions);
 	}
 
-	public CombinableArbitrary<?> getCachedArbitrary(Property property) {
+	public @Nullable CombinableArbitrary<?> getCachedArbitrary(Property property) {
 		CombinableArbitrary<?> javaTypeCombinableArbitrary = javaArbitrariesByProperty.get(property);
 		if (javaTypeCombinableArbitrary != null) {
 			return javaTypeCombinableArbitrary;

fixture-monkey-api/src/main/java/com/navercorp/fixturemonkey/api/context/MonkeyGeneratorContext.java

@@ -24,6 +24,7 @@
 
 import org.apiguardian.api.API;
 import org.apiguardian.api.API.Status;
+import org.jspecify.annotations.Nullable;
 
 import com.navercorp.fixturemonkey.api.generator.ArbitraryGeneratorContext;
 import com.navercorp.fixturemonkey.api.property.PropertyPath;
@@ -40,7 +41,8 @@ public MonkeyGeneratorContext(SortedMap<PropertyPath, Set<Object>> uniqueSetsByP
 		this.uniqueSetsByProperty = uniqueSetsByProperty;
 	}
 
-	public synchronized boolean isUniqueAndCheck(PropertyPath property, Object value) {
+	@SuppressWarnings("argument")
+	public synchronized boolean isUniqueAndCheck(PropertyPath property, @Nullable Object value) {
 		Set<Object> set = uniqueSetsByProperty.computeIfAbsent(property, p -> new HashSet<>());
 		boolean unique = !set.contains(value);
 		if (unique) {

fixture-monkey-api/src/main/java/com/navercorp/fixturemonkey/api/expression/ExpressionGenerator.java

@@ -28,6 +28,7 @@
 @API(since = "0.4.0", status = Status.MAINTAINED)
 @FunctionalInterface
 public interface ExpressionGenerator extends PropertySelector {
+	@SuppressWarnings("nullness")
 	default String generate() {
 		return this.generate(Property::getName);
 	}

fixture-monkey-api/src/main/java/com/navercorp/fixturemonkey/api/expression/JavaGetterPropertyFieldNameResolver.java

@@ -41,6 +41,7 @@ public String resolveFieldName(Class<?> targetClass, String methodName) {
 		return null;
 	}
 
+	@Nullable
 	private static String stripPrefixPropertyName(Class<?> targetClass, String methodName, int prefixLength) {
 		char[] ch = methodName.toCharArray();
 		ch[prefixLength] = Character.toLowerCase(ch[prefixLength]);

fixture-monkey-api/src/main/java/com/navercorp/fixturemonkey/api/expression/JavaGetterPropertySelectors.java

@@ -40,7 +40,7 @@ abstract class JavaGetterPropertySelectors {
 	/**
 	 * It is for internal use only. It can be changed or removed at any time.
 	 **/
-	@SuppressWarnings("unchecked")
+	@SuppressWarnings({"unchecked", "dereference.of.nullable", "argument"})
 	static <T, R> JavaGetterMethodPropertySelector<T, R> resolvePropertySelector(
 		JavaGetterMethodReference<T, R> methodRef
 	) {

fixture-monkey-api/src/main/java/com/navercorp/fixturemonkey/api/generator/ArbitraryGeneratorContext.java

@@ -54,6 +54,7 @@ public final class ArbitraryGeneratorContext implements Traceable {
 	private final BiFunction<ArbitraryGeneratorContext, ArbitraryProperty, CombinableArbitrary<?>> resolveArbitrary;
 	private final MonkeyGeneratorContext monkeyGeneratorContext;
 	private final LazyArbitrary<PropertyPath> lazyPropertyPath;
+	@SuppressWarnings("methodref.receiver.bound")
 	private final LazyArbitrary<Map<ArbitraryProperty, CombinableArbitrary<?>>> arbitraryListByArbitraryProperty =
 		LazyArbitrary.lazy(this::initArbitraryListByArbitraryProperty);
 	private final int generateUniqueMaxTries;
@@ -124,6 +125,7 @@ public Map<String, CombinableArbitrary<?>> getCombinableArbitrariesByResolvedNam
 			.collect(toMap(it -> it.getKey().getObjectProperty().getResolvedPropertyName(), Entry::getValue));
 	}
 
+	@SuppressWarnings("return")
 	public Map<String, CombinableArbitrary<?>> getCombinableArbitrariesByPropertyName() {
 		return arbitraryListByArbitraryProperty.getValue().entrySet().stream()
 			.collect(toMap(it -> it.getKey().getObjectProperty().getProperty().getName(), Entry::getValue));
@@ -142,7 +144,7 @@ public boolean isRootContext() {
 		return this.property.getObjectProperty().isRoot();
 	}
 
-	public synchronized boolean isUniqueAndCheck(PropertyPath property, Object value) {
+	public synchronized boolean isUniqueAndCheck(PropertyPath property, @Nullable Object value) {
 		return monkeyGeneratorContext.isUniqueAndCheck(property, value);
 	}