Implement error-prone for basic analysis

build.gradle.kts

@@ -1,3 +1,5 @@
+import net.ltgt.gradle.errorprone.errorprone
+
 plugins {
     `java-library`
     `maven-publish`
@@ -6,6 +8,7 @@ plugins {
     id("org.spongepowered.gradle.event-impl-gen")
     id("org.cadixdev.licenser")
     id("org.jetbrains.gradle.plugin.idea-ext")
+    id("net.ltgt.errorprone")
 }
 
 repositories {
@@ -38,6 +41,8 @@ val ap by sourceSets.registering {
 
 // Project dependencies
 dependencies {
+    val errorproneVersion: String by project
+
     // Directly tied to what's available from Minecraft
     api("org.apache.logging.log4j:log4j-api:2.8.1")
     api("com.google.guava:guava:21.0") {
@@ -111,6 +116,13 @@ dependencies {
         exclude(group = "com.google.inject", module = "guice")
     }
 
+    // Compile-time static analysis
+    compileOnly("com.google.errorprone:error_prone_annotations:$errorproneVersion")
+    errorprone("com.google.errorprone:error_prone_core:$errorproneVersion")
+    if (!JavaVersion.current().isJava9Compatible) { // for building with JDK 8
+        errorproneJavac("com.google.errorprone:javac:9+181-r4173-1")
+    }
+
     // Math library
     api("org.spongepowered:math:2.0.0-SNAPSHOT")
 
@@ -192,6 +204,12 @@ tasks {
         if (JavaVersion.current().isJava10Compatible) {
             options.release.set(8)
         }
+
+        options.errorprone {
+            disable("FutureReturnValueIgnored") // this check doesn't handle CompletableFuture properly
+            disable("EqualsGetClass") // conflicts with IntelliJ defaults
+            disable("MissingSummary") // TODO: Re-enable this check once Javadoc is in a better state
+        }
     }
 
     test {

gradle.properties

@@ -5,3 +5,5 @@ projectUrl=https://www.spongepowered.org
 projectDescription=A plugin API for Minecraft: Java Edition
 
 org.gradle.parallel=true
+
+errorproneVersion=2.6.0

settings.gradle.kts

@@ -10,5 +10,6 @@ pluginManagement {
         id("org.spongepowered.gradle.event-impl-gen") version "7.0.0"
         id("org.cadixdev.licenser") version "0.6.0"
         id("org.jetbrains.gradle.plugin.idea-ext") version "1.0"
+        id("net.ltgt.errorprone") version "2.0.1"
     }
 }

src/main/java/org/spongepowered/api/ResourceKey.java

@@ -213,6 +213,7 @@ default Builder namespace(PluginContainer container) {
          * @return The built resource key
          * @throws IllegalStateException If {@link Builder#namespace(String)} or {@link Builder#value(String)} are not set.
          */
+        @Override
         ResourceKey build() throws IllegalStateException;
     }
 

src/main/java/org/spongepowered/api/ResourceKeyed.java

@@ -28,6 +28,7 @@
 
 public interface ResourceKeyed extends Keyed {
 
+    @Override
     ResourceKey key();
 
 }

src/main/java/org/spongepowered/api/advancement/DisplayInfo.java

@@ -222,6 +222,7 @@ default Builder icon(ItemStack itemStack) {
          *
          * @return The display info
          */
+        @Override
         DisplayInfo build();
 
     }

src/main/java/org/spongepowered/api/advancement/criteria/AdvancementCriterion.java

@@ -162,6 +162,7 @@ interface BaseBuilder<T extends AdvancementCriterion, B extends BaseBuilder<T, B
          *
          * @return The criterion
          */
+        @Override
         T build();
     }
 

src/main/java/org/spongepowered/api/advancement/criteria/trigger/FilteredTrigger.java

@@ -88,6 +88,7 @@ interface Builder<C extends FilteredTriggerConfiguration> extends org.spongepowe
          *
          * @return The trigger
          */
+        @Override
         FilteredTrigger<C> build();
     }
 

src/main/java/org/spongepowered/api/adventure/Audiences.java

@@ -49,7 +49,7 @@ public static Audience server() {
      * @return An audience
      */
     public static Audience onlinePlayers() {
-        return Sponge.game().factoryProvider().provide(Factory.class).onlinePlayers();
+        return Audiences.factory().onlinePlayers();
     }
 
     /**
@@ -61,7 +61,7 @@ public static Audience onlinePlayers() {
      */
     public static Audience withPermission(final String permission) {
         Objects.requireNonNull(permission);
-        return Sponge.game().factoryProvider().provide(Factory.class).withPermission(permission);
+        return Audiences.factory().withPermission(permission);
     }
 
     /**

src/main/java/org/spongepowered/api/block/entity/BlockEntityArchetype.java

@@ -182,6 +182,7 @@ default Builder blockEntity(Supplier<? extends BlockEntityType> type) {
          *
          * @return The new instance
          */
+        @Override
         BlockEntityArchetype build();
 
     }

src/main/java/org/spongepowered/api/block/transaction/BlockTransaction.java

@@ -83,7 +83,7 @@ public boolean equals(final Object obj) {
         final BlockTransaction other = (BlockTransaction) obj;
         return Objects.equals(this.original(), other.original())
             && Objects.equals(this.defaultReplacement(), other.defaultReplacement())
-            && Objects.equals(this.isValid(), other.isValid())
+            && this.isValid() == other.isValid()
             && Objects.equals(this.custom(), other.custom())
             && Objects.equals(this.operation, other.operation);
     }

src/main/java/org/spongepowered/api/command/Command.java

@@ -176,7 +176,7 @@ default Optional<Component> help(@NonNull final CommandCause cause) {
      * Gets the usage string of this command.
      *
      * <p>A usage string may look like
-     * {@code [&lt;world&gt;] &lt;var1&gt; &lt;var2&gt;}.</p>
+     * {@code [<world>] <var1> <var2>}.</p>
      *
      * <p>The string must not contain the command alias.</p>
      *
@@ -606,6 +606,7 @@ default Builder shortDescription(@Nullable final Component description) {
          * @return The command, ready for registration
          * @throws IllegalStateException if the builder is not complete
          */
+        @Override
         Command.Parameterized build();
 
     }

src/main/java/org/spongepowered/api/command/CommandCause.java

@@ -257,6 +257,7 @@ default List<Object> all() {
      *
      * @return The {@link Subject} responsible, if any.
      */
+    @Override
     Subject subject();
 
     /**

src/main/java/org/spongepowered/api/command/CommandResult.java

@@ -132,6 +132,7 @@ interface Builder extends org.spongepowered.api.util.Builder<CommandResult, Buil
          *
          * @return A CommandResult with the specified settings
          */
+        @Override
         CommandResult build();
 
     }

src/main/java/org/spongepowered/api/command/parameter/CommonParameters.java

@@ -41,7 +41,7 @@
  * </p>
  * 
  * <pre> {@code
- * final Parameter.Value&lt;ServerPlayer&gt; parameter = Parameter.player().setKey("player").build();
+ * final Parameter.Value<ServerPlayer> parameter = Parameter.player().setKey("player").build();
  * final Command.Parameterized builder = Command.builder()
  *      .parameter(parameter)
  *      .executor(context -> {

src/main/java/org/spongepowered/api/command/parameter/Parameter.java

@@ -1255,6 +1255,7 @@ default <V extends ValueParser<? extends T>> Builder<T> addParser(@NonNull final
              *
              * @return The {@link Parameter}
              */
+            @Override
             Parameter.Value<T> build();
 
         }
@@ -1311,6 +1312,7 @@ interface Builder extends org.spongepowered.api.util.Builder<Subcommand, Builder
              *
              * @return The {@link Subcommand}
              */
+            @Override
             Subcommand build();
 
         }
@@ -1395,6 +1397,7 @@ default SequenceBuilder then(@NonNull final Iterable<Parameter> parameters) {
          *
          * @return The {@link Parameter}
          */
+        @Override
         Multi build();
 
     }
@@ -1467,6 +1470,7 @@ default FirstOfBuilder orFirstOf(@NonNull final Iterable<Parameter> parameters)
          *
          * @return The {@link Multi}
          */
+        @Override
         Multi build();
 
     }

src/main/java/org/spongepowered/api/command/parameter/managed/Flag.java

@@ -224,6 +224,7 @@ default Builder aliases(final String... aliases) {
          * @return A {@link Flag}
          * @throws IllegalStateException if no key or no alias is specified
          */
+        @Override
         Flag build() throws IllegalStateException;
 
     }

src/main/java/org/spongepowered/api/command/parameter/managed/standard/VariableValueParameters.java

@@ -294,6 +294,7 @@ public interface RegistryEntryBuilder<T> extends Builder<ValueParameter<T>, Regi
          *
          * @return The {@link ValueParameter}
          */
+        @Override
         ValueParameter<T> build();
 
     }
@@ -367,6 +368,7 @@ default StaticChoicesBuilder<T> addChoices(final Map<String, ? extends T> choice
          * @return The {@link ValueParameter}
          * @throws IllegalStateException if no choices have been specified
          */
+        @Override
         ValueParameter<T> build();
 
     }
@@ -424,6 +426,7 @@ public interface DynamicChoicesBuilder<T> extends Builder<ValueParameter<T>, Dyn
          * @return The {@link ValueParameter}
          * @throws IllegalStateException if no choices have been specified
          */
+        @Override
         ValueParameter<T> build();
 
     }
@@ -483,6 +486,7 @@ default LiteralBuilder<T> returnValue(final T returnValue) {
          * @throws IllegalStateException if the literal and the return object
          *             have not been specified
          */
+        @Override
         ValueParameter<T> build();
 
     }
@@ -533,6 +537,7 @@ public interface TextBuilder extends Builder<ValueParameter<Component>, TextBuil
          * @throws IllegalStateException if the {@link ComponentSerializer} has not
          *             been specified
          */
+        @Override
         ValueParameter<Component> build() throws IllegalStateException;
 
     }
@@ -572,6 +577,7 @@ public interface NumberRangeBuilder<T extends Number> extends Builder<ValueParam
          * @throws IllegalStateException if the minimum is greater than the
          *              maximum
          */
+        @Override
         ValueParameter<T> build();
 
     }

src/main/java/org/spongepowered/api/command/selector/Selector.java

@@ -476,6 +476,7 @@ interface Builder extends org.spongepowered.api.util.Builder<Selector, Builder>
          * @throws IllegalStateException if the builder could not create a
          *                               selector
          */
+        @Override
         Selector build() throws IllegalStateException;
 
     }

src/main/java/org/spongepowered/api/data/DataTransactionResult.java

@@ -699,6 +699,7 @@ public Builder absorbResult(final DataTransactionResult result) {
          *
          * @return The newly created transaction result
          */
+        @Override
         public DataTransactionResult build() {
             if (this.resultType == null) {
                 throw new IllegalStateException("ResultType must be set!");

src/main/java/org/spongepowered/api/data/ImmutableDataProviderBuilder.java

@@ -46,5 +46,6 @@ public interface ImmutableDataProviderBuilder<H extends DataHolder, V extends Va
 
     ImmutableDataProviderBuilder<H, V, E> supports(final Function<H, Boolean> supports);
 
+    @Override
     DataProvider<? extends Value<E>, E> build();
 }

src/main/java/org/spongepowered/api/data/KeyValueMatcher.java

@@ -219,6 +219,7 @@ interface Builder<V> extends org.spongepowered.api.util.Builder<KeyValueMatcher<
          *
          * @return The key value matcher
          */
+        @Override
         KeyValueMatcher<V> build();
     }
 }

src/main/java/org/spongepowered/api/data/Keys.java

@@ -1007,11 +1007,14 @@ public final class Keys {
      *
      * <p>The format of the rotation is represented by:</p>
      *
-     * <ul><li>{@code x -&gt; pitch</code></li><li> <code>y -&gt; yaw</code></li><li><code>z -&gt; roll
-     * }</li></ul>
+     * <ul>
+     *     <li>{@code x -> pitch}</li>
+     * <li> {@code y -> yaw}</li>
+     * <li>{@code z -> roll}</li>
+     * </ul>
      *
      * <p>Note that the pitch will be the same x value returned by
-     * {@link Entity#rotation ()} and Minecraft does not currently support
+     * {@link Entity#rotation()} and Minecraft does not currently support
      * head roll so the z value will always be zero.</p>
      */
     public static final Key<Value<Vector3d>> HEAD_ROTATION = Keys.key(ResourceKey.sponge("head_rotation"), TypeTokens.VECTOR_3D_VALUE_TOKEN);

src/main/java/org/spongepowered/api/data/MutableDataProviderBuilder.java

@@ -63,5 +63,6 @@ public interface MutableDataProviderBuilder<H extends DataHolder.Mutable, V exte
 
     MutableDataProviderBuilder<H, V, E> supports(final Function<H, Boolean> supports);
 
+    @Override
     DataProvider<V, E> build();
 }

src/main/java/org/spongepowered/api/data/SerializableDataHolder.java

@@ -54,7 +54,7 @@ public interface SerializableDataHolder extends DataSerializable, CopyableDataHo
     @Override
     SerializableDataHolder copy();
 
-    interface Mutable extends SerializableDataHolder, CopyableDataHolder.Mutable {
+    interface Mutable extends SerializableDataHolder, DataHolder.Mutable {
 
         /**
          * Attempts to set all data of this {@link DataHolder} according to the

src/main/java/org/spongepowered/api/data/Transaction.java

@@ -175,7 +175,7 @@ public int hashCode() {
 
     @SuppressWarnings("rawtypes")
     @Override
-    public boolean equals(Object obj) {
+    public boolean equals(final @Nullable Object obj) {
         if (this == obj) {
             return true;
         }
@@ -185,7 +185,7 @@ public boolean equals(Object obj) {
         final Transaction other = (Transaction) obj;
         return Objects.equals(this.original, other.original)
                && Objects.equals(this.defaultReplacement, other.defaultReplacement)
-               && Objects.equals(this.valid, other.valid)
+               && this.valid == other.valid
                && Objects.equals(this.custom, other.custom);
     }
 

src/main/java/org/spongepowered/api/data/meta/BannerPatternLayer.java

@@ -150,6 +150,7 @@ default Builder color(Supplier<? extends DyeColor> color) {
          *
          * @return The new pattern layer
          */
+        @Override
         BannerPatternLayer build();
 
         @Override

src/main/java/org/spongepowered/api/data/persistence/DataView.java

@@ -350,6 +350,7 @@ default Optional<List<ResourceKey>> getResourceKeyList(final DataQuery path) {
             try {
                 keys.add(ResourceKey.resolve(s));
             } catch (final Exception ignored) {
+                // skip invalid keys
             }
         }
 

src/main/java/org/spongepowered/api/data/persistence/Queries.java

@@ -26,6 +26,7 @@
 
 import static org.spongepowered.api.data.persistence.DataQuery.of;
 
+@SuppressWarnings("BadImport")
 public final class Queries {
 
     // Content version

src/main/java/org/spongepowered/api/effect/particle/ParticleEffect.java

@@ -198,6 +198,7 @@ default Builder quantity(int quantity) throws IllegalArgumentException {
          *
          * @return A new instance of a ParticleEffect
          */
+        @Override
         ParticleEffect build();
     }
 }

src/main/java/org/spongepowered/api/effect/potion/PotionEffect.java

@@ -198,6 +198,7 @@ default Builder potionType(Supplier<? extends PotionEffectType> potionEffectType
          * @return A new instance of a PotionEffect
          * @throws IllegalStateException If the potion effect is not completed
          */
+        @Override
         PotionEffect build() throws IllegalStateException;
     }
 }

src/main/java/org/spongepowered/api/entity/ai/goal/AbstractGoal.java

@@ -69,7 +69,7 @@ public abstract class AbstractGoal<O extends Agent> implements Goal<O> {
      *
      * @param type The type
      */
-    public AbstractGoal(GoalType type) {
+    protected AbstractGoal(final GoalType type) {
         Objects.requireNonNull(type);
         this.type = type;
     }