Fix removal of bindings in ProvisionListenerCallbackStore and simplify

Bindings have never been removed from the cache in
ProvisionListenerCallbackStore.remove() because the key of the cache
were KeyBinding objects, while it was attempted to remove Binding
objects.

Additionally use a standard Java ConcurrentHashMap instead of a simple
Guava Cache, which also allows to remove the now unnecessary KeyBinding
helper class. Instead of a new KeyBinding object a new new lambda object
is created for each cache lookup.

core/src/com/google/inject/internal/ProvisionListenerCallbackStore.java

@@ -16,9 +16,6 @@
 
 package com.google.inject.internal;
 
-import com.google.common.cache.CacheBuilder;
-import com.google.common.cache.CacheLoader;
-import com.google.common.cache.LoadingCache;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Lists;
@@ -29,6 +26,8 @@
 import com.google.inject.spi.ProvisionListener;
 import com.google.inject.spi.ProvisionListenerBinding;
 import java.util.List;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.logging.Logger;
 
 /**
@@ -45,15 +44,7 @@ final class ProvisionListenerCallbackStore {
 
   private final ImmutableList<ProvisionListenerBinding> listenerBindings;
 
-  private final LoadingCache<KeyBinding, ProvisionListenerStackCallback<?>> cache =
-      CacheBuilder.newBuilder()
-          .build(
-              new CacheLoader<KeyBinding, ProvisionListenerStackCallback<?>>() {
-                @Override
-                public ProvisionListenerStackCallback<?> load(KeyBinding key) {
-                  return create(key.binding);
-                }
-              });
+  private final Map<Key<?>, ProvisionListenerStackCallback<?>> cache = new ConcurrentHashMap<>();
 
   ProvisionListenerCallbackStore(List<ProvisionListenerBinding> listenerBindings) {
     this.listenerBindings = ImmutableList.copyOf(listenerBindings);
@@ -63,14 +54,12 @@ public ProvisionListenerStackCallback<?> load(KeyBinding key) {
    * Returns a new {@link ProvisionListenerStackCallback} for the key or {@code null} if there are
    * no listeners
    */
-  @SuppressWarnings(
-      "unchecked") // the ProvisionListenerStackCallback type always agrees with the passed type
+  @SuppressWarnings("unchecked") // the ProvisionListenerStackCallback type always agrees with the passed type
   public <T> ProvisionListenerStackCallback<T> get(Binding<T> binding) {
     // Never notify any listeners for internal bindings.
     if (!INTERNAL_BINDINGS.contains(binding.getKey())) {
-      ProvisionListenerStackCallback<T> callback =
-          (ProvisionListenerStackCallback<T>)
-              cache.getUnchecked(new KeyBinding(binding.getKey(), binding));
+      ProvisionListenerStackCallback<T> callback = (ProvisionListenerStackCallback<T>) cache
+          .computeIfAbsent(binding.getKey(), k -> create(binding));
       return callback.hasListeners() ? callback : null;
     }
     return null;
@@ -86,7 +75,7 @@ public <T> ProvisionListenerStackCallback<T> get(Binding<T> binding) {
    * <p>Returns true if the type was stored in the cache, false otherwise.
    */
   boolean remove(Binding<?> type) {
-    return cache.asMap().remove(type) != null;
+    return cache.remove(type.getKey()) != null;
   }
 
   /**
@@ -107,27 +96,7 @@ private <T> ProvisionListenerStackCallback<T> create(Binding<T> binding) {
       // no listeners.
       return ProvisionListenerStackCallback.emptyListener();
     }
-    return new ProvisionListenerStackCallback<T>(binding, listeners);
+    return new ProvisionListenerStackCallback<>(binding, listeners);
   }
 
-  /** A struct that holds key and binding but uses just key for equality/hashcode. */
-  private static class KeyBinding {
-    final Key<?> key;
-    final Binding<?> binding;
-
-    KeyBinding(Key<?> key, Binding<?> binding) {
-      this.key = key;
-      this.binding = binding;
-    }
-
-    @Override
-    public boolean equals(Object obj) {
-      return obj instanceof KeyBinding && key.equals(((KeyBinding) obj).key);
-    }
-
-    @Override
-    public int hashCode() {
-      return key.hashCode();
-    }
-  }
 }