Add HuntBugs static analyzer and fix warnings

HuntBugs is the unofficial successor to Findbugs on a clean code base.
The remaining warnings are all false positives and not sure how to
suppress individually. It did find a few mistakes where the array was
checked for null, rather than its element (weak key null guard).

See https://github.com/amaembo/huntbugs for details.

caffeine/src/main/java/com/github/benmanes/caffeine/cache/BoundedLocalCache.java

@@ -1634,7 +1634,7 @@ V putSlow(K key, V value, int newWeight, boolean notifyWriter, boolean onlyIfAbs
         nodeKey[0] = n.getKey();
         oldValue[0] = n.getValue();
         oldWeight[0] = n.getWeight();
-        if ((nodeKey == null) || (oldValue[0] == null)) {
+        if ((nodeKey[0] == null) || (oldValue[0] == null)) {
           cause[0] = RemovalCause.COLLECTED;
         } else if (hasExpired(n, now)) {
           cause[0] = RemovalCause.EXPIRED;
@@ -1994,7 +1994,7 @@ V doComputeIfAbsent(K key, Object keyRef,
         nodeKey[0] = n.getKey();
         weight[0] = n.getWeight();
         oldValue[0] = n.getValue();
-        if ((nodeKey == null) || (oldValue[0] == null)) {
+        if ((nodeKey[0] == null) || (oldValue[0] == null)) {
           cause[0] = RemovalCause.COLLECTED;
         } else if (hasExpired(n, now)) {
           cause[0] = RemovalCause.EXPIRED;
@@ -2141,7 +2141,7 @@ V remap(K key, Object keyRef, BiFunction<? super K, ? super V, ? extends V> rema
       synchronized (n) {
         nodeKey[0] = n.getKey();
         oldValue[0] = n.getValue();
-        if ((nodeKey == null) || (oldValue[0] == null)) {
+        if ((nodeKey[0] == null) || (oldValue[0] == null)) {
           cause[0] = RemovalCause.COLLECTED;
         } else if (hasExpired(n, now)) {
           cause[0] = RemovalCause.EXPIRED;

caffeine/src/main/java/com/github/benmanes/caffeine/cache/CaffeineSpec.java

@@ -182,7 +182,7 @@ void configure(String key, @Nullable String value) {
         maximumWeight(key, value);
         return;
       case "weakKeys":
-        weakKeys(key, value);
+        weakKeys(value);
         return;
       case "weakValues":
         valueStrength(key, value, Strength.WEAK);
@@ -200,7 +200,7 @@ void configure(String key, @Nullable String value) {
         refreshAfterWrite(key, value);
         return;
       case "recordStats":
-        recordStats(key, value);
+        recordStats(value);
         return;
       default:
         throw new IllegalArgumentException("Unknown key " + key);
@@ -233,7 +233,7 @@ void maximumWeight(String key, String value) {
   }
 
   /** Configures the keys as weak references. */
-  void weakKeys(String key, @Nullable String value) {
+  void weakKeys(@Nullable String value) {
     requireArgument(value == null, "weak keys does not take a value");
     requireArgument(keyStrength == null, "weak keys was already set");
     keyStrength = Strength.WEAK;
@@ -268,7 +268,7 @@ void refreshAfterWrite(String key, String value) {
   }
 
   /** Configures the value as weak or soft references. */
-  void recordStats(String key, @Nullable String value) {
+  void recordStats(@Nullable String value) {
     requireArgument(value == null, "record stats does not take a value");
     requireArgument(!recordStats, "record stats was already set");
     recordStats = true;

gradle/code_quality.gradle

@@ -2,6 +2,7 @@
  * Configurations for code quality analysis
  */
 apply plugin: 'org.kordamp.gradle.stats'
+apply plugin: 'one.util.huntbugs'
 apply plugin: 'checkstyle'
 apply plugin: 'findbugs'
 apply plugin: 'jacoco'
@@ -32,6 +33,12 @@ checkstyle {
   config = resources.text.fromArchiveEntry(configurations.checkstyleConfig, 'google_checks.xml')
 }
 
+huntbugs {
+  classSimpleFilter { classname ->
+    !classname.contains('Header') && !classname.contains('Mpsc') && !classname.contains('Factory')
+  }
+}
+
 findbugs {
   effort = 'max'
   excludeFilter = file("${rootDir}/config/findbugs/exclude.xml")

gradle/dependencies.gradle

@@ -73,6 +73,8 @@ ext {
     coveralls: '2.6.3',
     extra_conf: '3.1.0',
     error_prone: '0.0.8',
+    huntbugs_core: '0.0.11',
+    huntbugs_plugin: '0.3.5',
     jmh: '0.3.0',
     nexus: '2.3.1',
     pmd: '5.5.1',
@@ -164,6 +166,10 @@ ext {
     coveralls: "org.kt3k.gradle.plugin:coveralls-gradle-plugin:${plugin_versions.coveralls}",
     extra_conf: "com.netflix.nebula:gradle-extra-configurations-plugin:${plugin_versions.extra_conf}",
     error_prone: "net.ltgt.gradle:gradle-errorprone-plugin:${plugin_versions.error_prone}",
+    huntbugs: [
+      "one.util:huntbugs:${plugin_versions.huntbugs_core}",
+      "gradle.plugin.one.util.huntbugs:huntbugs-gradle-plugin:${plugin_versions.huntbugs_plugin}",
+    ],
     jmh: "gradle.plugin.me.champeau.gradle:jmh-gradle-plugin:${plugin_versions.jmh}",
     nexus: "com.bmuschko:gradle-nexus-plugin:${plugin_versions.nexus}",
     semantic_versioning: "io.ehdev:gradle-semantic-versioning:${plugin_versions.semantic_versioning}",

simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/admission/table/RandomRemovalFrequencyTable.java

@@ -81,7 +81,7 @@ public void increment(long e) {
     // just a model.
     if (currSum == maxSum) {
       List<Long> array = new ArrayList<>(table.keySet());
-      long itemToRemove = array.get(random.nextInt(array.size()));
+      Long itemToRemove = array.get(random.nextInt(array.size()));
       value = table.remove(itemToRemove);
 
       if (value > 1) {

simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/admission/tinycache/HashFunctionParser.java

@@ -50,7 +50,7 @@ public HashedItem createHash(long item) {
     h ^= item;
     h *= m;
 
-    fpaux.fingerprint = (byte) (h & fpMask);
+    fpaux.fingerprint = (byte) h;
     // the next line is a dirty fix as I do not want the value of 0 as a fingerprint.
     // It can be eliminated if we want very short fingerprints.
     fpaux.fingerprint = (fpaux.fingerprint == 0L) ? 1 : fpaux.fingerprint;

simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/admission/tinycache/TinyCacheAdapter.java

@@ -27,8 +27,6 @@
 public final class TinyCacheAdapter implements Frequency {
   // the actual data structure.
   TinyCacheSketch tcs;
-  // number of (independent sets)
-  int nrSets;
   // size between cache and sample.
   static final int sampleFactor = 10;
   // max frequency estimation of an item.
@@ -39,7 +37,7 @@ public final class TinyCacheAdapter implements Frequency {
    */
   public TinyCacheAdapter(Config config) {
     BasicSettings settings = new BasicSettings(config);
-    nrSets = sampleFactor * settings.maximumSize() / 64;
+    int nrSets = sampleFactor * settings.maximumSize() / 64; // number of (independent sets)
     tcs = new TinyCacheSketch(nrSets, 64,settings.randomSeed());
   }
 

simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/admission/tinycache/TinyCacheWithGhostCache.java

@@ -26,13 +26,14 @@
  */
 @SuppressWarnings("PMD.AvoidDollarSigns")
 public final class TinyCacheWithGhostCache {
+  private static final int sampleSize = 10;
+
   public final long[] chainIndex;
   public final long[] isLastIndex;
   private final HashFunctionParser hashFunc;
   private final int itemsPerSet;
   private final long[] cache;
   private final Random rnd;
-  private final int sampleSize;
   private final TinyCacheSketch ghostCache;
 
   public TinyCacheWithGhostCache(int nrSets, int itemsPerSet, int randomSeed) {
@@ -41,7 +42,6 @@ public TinyCacheWithGhostCache(int nrSets, int itemsPerSet, int randomSeed) {
     hashFunc = new HashFunctionParser(nrSets);
     this.itemsPerSet = itemsPerSet;
     cache = new long[nrSets * itemsPerSet];
-    sampleSize = 10;
     ghostCache = new TinyCacheSketch(nrSets * sampleSize, itemsPerSet, randomSeed + 1);
     rnd = new Random(randomSeed);
   }

simulator/src/main/java/com/github/benmanes/caffeine/cache/simulator/policy/linked/MultiQueuePolicy.java

@@ -138,6 +138,10 @@ private void evict() {
         break;
       }
     }
+    if (victim == null) {
+      return;
+    }
+
     victim.remove();
     data.remove(victim.key);
     out.put(victim.key, victim);