Refactor: separate SplittableTruncateSizedRestrictions

Author: kennknowles

sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/splittabledofn/RestrictionTracker.java

@@ -211,6 +211,6 @@ public static <RestrictionT> TruncateResult of(RestrictionT restriction) {
       return new AutoValue_RestrictionTracker_TruncateResult(restriction);
     }
 
-    public abstract @Nullable RestrictionT getTruncatedRestriction();
+    public abstract RestrictionT getTruncatedRestriction();
   }
 }

sdks/java/core/src/main/java/org/apache/beam/sdk/values/KV.java

@@ -40,6 +40,7 @@
  */
 public class KV<K, V> implements Serializable {
   /** Returns a {@link KV} with the given key and value. */
+  @Pure
   public static <K, V> KV<K, V> of(K key, V value) {
     return new KV<>(key, value);
   }

sdks/java/core/src/main/java/org/apache/beam/sdk/values/WindowedValue.java

@@ -20,6 +20,7 @@
 import java.util.Collection;
 import org.apache.beam.sdk.transforms.windowing.BoundedWindow;
 import org.apache.beam.sdk.transforms.windowing.PaneInfo;
+import org.checkerframework.dataflow.qual.Pure;
 import org.joda.time.Instant;
 
 /**
@@ -29,26 +30,32 @@
  */
 public interface WindowedValue<T> {
   /** The primary data for this value. */
+  @Pure
   T getValue();
 
   /** The timestamp of this value in event time. */
+  @Pure
   Instant getTimestamp();
 
   /** Returns the windows of this {@code WindowedValue}. */
+  @Pure
   Collection<? extends BoundedWindow> getWindows();
 
   /** The {@link PaneInfo} associated with this WindowedValue. */
+  @Pure
   PaneInfo getPaneInfo();
 
   /**
    * A representation of each of the actual values represented by this compressed {@link
    * WindowedValue}, one per window.
    */
+  @Pure
   Iterable<WindowedValue<T>> explodeWindows();
 
   /**
    * A {@link WindowedValue} with identical metadata to the current one, but with the provided
    * value.
    */
+  @Pure
   <OtherT> WindowedValue<OtherT> withValue(OtherT value);
 }