Merge pull request #461 from janeisklar/lombok-support-cached-hashcode

#460: Add support for @EqualsAndHashCode(cacheStrategy = LAZY)

Author: jqno

docs/_errormessages/significant-fields-equals-relies-on-foo-but-hashcode-does-not.md

@@ -51,4 +51,21 @@ EqualsVerifier.forClass(CachedHashCode.class)
     .withCachedHashCode("cachedHashCode", "calculateHashCode", new CachedHashCode());
 {% endhighlight %}
 
+Another scenario in which you might experience this error message is when using Lombok's `@EqualsAndHashCode` with `cacheStrategy=LAZY`: 
+
+{% highlight java %}
+@RequiredArgsConstructor
+@EqualsAndHashCode(cacheStrategy = EqualsAndHashCode.CacheStrategy.LAZY)
+public class CachedHashCode {
+  private final String foo;
+}
+{% endhighlight %}
+
+Using `.withLombokCachedHashCode` allows to test those classes as well: 
+
+{% highlight java %}
+EqualsVerifier.forClass(LazyPojo.class)
+    .withLombokCachedHashCode(new CachedHashCode("bar"));
+{% endhighlight %}
+
 For more help on how to use `withCachedHashCode`, read the [manual page about it](/equalsverifier/manual/caching-hashcodes).

src/main/java/nl/jqno/equalsverifier/api/SingleTypeEqualsVerifierApi.java

@@ -278,6 +278,20 @@ public SingleTypeEqualsVerifierApi<T> withCachedHashCode(
         return this;
     }
 
+    /**
+     * Signals that T uses Lombok to cache its hashCode, instead of re-calculating it each time the
+     * {@code hashCode()} method is called.
+     *
+     * @param example An instance of the class under test, to verify that the hashCode has been
+     *     initialized properly.
+     * @return {@code this}, for easy method chaining.
+     * @see #withCachedHashCode(String, String, T)
+     */
+    public SingleTypeEqualsVerifierApi<T> withLombokCachedHashCode(T example) {
+        cachedHashCodeInitializer = CachedHashCodeInitializer.lombokCachedHashcode(example);
+        return this;
+    }
+
     /**
      * Performs the verification of the contracts for {@code equals} and {@code hashCode} and throws
      * an {@link AssertionError} if there is a problem.

src/main/java/nl/jqno/equalsverifier/internal/util/CachedHashCodeInitializer.java

@@ -30,10 +30,19 @@ public class CachedHashCodeInitializer<T> {
     private final T example;
 
     private CachedHashCodeInitializer() {
-        this.passthrough = true;
-        this.cachedHashCodeField = null;
-        this.calculateMethod = null;
-        this.example = null;
+        this(true, null, null, null);
+    }
+
+    private CachedHashCodeInitializer(
+        boolean passthrough,
+        Field cachedHashCodeField,
+        Method calculateMethod,
+        T example
+    ) {
+        this.passthrough = passthrough;
+        this.cachedHashCodeField = cachedHashCodeField;
+        this.calculateMethod = calculateMethod;
+        this.example = example;
     }
 
     public CachedHashCodeInitializer(
@@ -44,14 +53,25 @@ public CachedHashCodeInitializer(
     ) {
         this.passthrough = false;
         this.cachedHashCodeField = findCachedHashCodeField(type, cachedHashCodeField);
-        this.calculateMethod = findCalculateHashCodeMethod(type, calculateHashCodeMethod);
+        this.calculateMethod = findCalculateHashCodeMethod(type, calculateHashCodeMethod, false);
         this.example = example;
     }
 
     public static <T> CachedHashCodeInitializer<T> passthrough() {
         return new CachedHashCodeInitializer<>();
     }
 
+    public static <T> CachedHashCodeInitializer<T> lombokCachedHashcode(T example) {
+        @SuppressWarnings("unchecked")
+        final Class<T> type = (Class<T>) example.getClass();
+        return new CachedHashCodeInitializer<>(
+            false,
+            findCachedHashCodeField(type, "$hashCodeCache"),
+            findCalculateHashCodeMethod(type, "hashCode", true),
+            example
+        );
+    }
+
     public boolean isPassthrough() {
         return passthrough;
     }
@@ -85,7 +105,7 @@ private void recomputeCachedHashCode(Object object) {
         );
     }
 
-    private Field findCachedHashCodeField(Class<?> type, String cachedHashCodeFieldName) {
+    private static Field findCachedHashCodeField(Class<?> type, String cachedHashCodeFieldName) {
         for (Field candidateField : FieldIterable.of(type)) {
             if (candidateField.getName().equals(cachedHashCodeFieldName)) {
                 if (
@@ -104,12 +124,16 @@ private Field findCachedHashCodeField(Class<?> type, String cachedHashCodeFieldN
         );
     }
 
-    private Method findCalculateHashCodeMethod(Class<?> type, String calculateHashCodeMethodName) {
+    private static Method findCalculateHashCodeMethod(
+        Class<?> type,
+        String calculateHashCodeMethodName,
+        boolean acceptPublicMethod
+    ) {
         for (Class<?> currentClass : SuperclassIterable.ofIncludeSelf(type)) {
             try {
                 Method method = currentClass.getDeclaredMethod(calculateHashCodeMethodName);
                 if (
-                    !Modifier.isPublic(method.getModifiers()) &&
+                    (acceptPublicMethod || !Modifier.isPublic(method.getModifiers())) &&
                     method.getReturnType().equals(int.class)
                 ) {
                     method.setAccessible(true);

src/test/java/nl/jqno/equalsverifier/integration/extra_features/LombokLazyEqualsAndHashcodeTest.java

@@ -0,0 +1,127 @@
+package nl.jqno.equalsverifier.integration.extra_features;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.core.StringContains.containsString;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import nl.jqno.equalsverifier.EqualsVerifier;
+import nl.jqno.equalsverifier.Warning;
+import org.junit.jupiter.api.Test;
+
+// CHECKSTYLE OFF: LocalFinalVariableName
+// CHECKSTYLE OFF: MemberName
+// CHECKSTYLE OFF: NeedBraces
+
+public class LombokLazyEqualsAndHashcodeTest {
+
+    @Test
+    void testWithLombokCachedHashCode() {
+        EqualsVerifier
+            .forClass(LazyPojo.class)
+            .withLombokCachedHashCode(new LazyPojo("a", new Object()))
+            .suppress(Warning.STRICT_INHERITANCE)
+            .verify();
+    }
+
+    @Test
+    void testDefaultEqualsVerifierFailsForCachedLombokEqualsAndHashcode() {
+        final AssertionError error = assertThrows(
+            AssertionError.class,
+            () ->
+                EqualsVerifier
+                    .forClass(LazyPojo.class)
+                    .suppress(Warning.STRICT_INHERITANCE)
+                    .verify()
+        );
+        assertThat(
+            error.getMessage(),
+            containsString("hashCode relies on $hashCodeCache, but equals does not.")
+        );
+    }
+
+    @Test
+    void testDefaultEqualsVerifierFailsForCachedLombokEqualsAndHashcodeWhenUsingWithCachedHashCode() {
+        final IllegalArgumentException error = assertThrows(
+            IllegalArgumentException.class,
+            () ->
+                EqualsVerifier
+                    .forClass(LazyPojo.class)
+                    .suppress(Warning.STRICT_INHERITANCE)
+                    .withCachedHashCode(
+                        "$hashCodeCache",
+                        "hashCode",
+                        new LazyPojo("bar", new Object())
+                    )
+                    .verify()
+        );
+        assertThat(
+            error.getMessage(),
+            containsString(
+                "Cached hashCode: Could not find calculateHashCodeMethod: must be 'private int hashCode()'"
+            )
+        );
+    }
+
+    /**
+     * This class has been generated with Lombok (1.18.20). It is equivalent to:
+     * <pre>
+     *   &#64;RequiredArgsConstructor
+     *   &#64;EqualsAndHashCode(cacheStrategy = EqualsAndHashCode.CacheStrategy.LAZY)
+     *   public class LazyPojo {
+     *
+     *     private final String foo;
+     *
+     *     private final Object bar;
+     *   }
+     * </pre>
+     */
+    @SuppressWarnings({ "RedundantIfStatement", "EqualsReplaceableByObjectsCall" })
+    private static class LazyPojo {
+
+        private transient int $hashCodeCache;
+
+        private final String foo;
+        private final Object bar;
+
+        public LazyPojo(String foo, Object bar) {
+            this.foo = foo;
+            this.bar = bar;
+        }
+
+        @Override
+        public boolean equals(final Object o) {
+            if (o == this) return true;
+            if (!(o instanceof LazyPojo)) return false;
+            final LazyPojo other = (LazyPojo) o;
+            if (!other.canEqual(this)) return false;
+            final Object this$foo = this.foo;
+            final Object other$foo = other.foo;
+            if (this$foo == null ? other$foo != null : !this$foo.equals(other$foo)) return false;
+            final Object this$bar = this.bar;
+            final Object other$bar = other.bar;
+            if (this$bar == null ? other$bar != null : !this$bar.equals(other$bar)) return false;
+            return true;
+        }
+
+        protected boolean canEqual(Object other) {
+            return other instanceof LazyPojo;
+        }
+
+        @Override
+        public int hashCode() {
+            if (this.$hashCodeCache != 0) {
+                return this.$hashCodeCache;
+            } else {
+                final int PRIME = 59;
+                int result = 1;
+                final Object $foo = this.foo;
+                result = result * PRIME + ($foo == null ? 43 : $foo.hashCode());
+                final Object $bar = this.bar;
+                result = result * PRIME + ($bar == null ? 43 : $bar.hashCode());
+
+                this.$hashCodeCache = result;
+                return result;
+            }
+        }
+    }
+}