return future instanceof FluentFuture
        ? (FluentFuture<V>) future
        : new ForwardingFluentFuture<V>(future);
  }

  /**
   * Simply returns its argument.
   *
   * @deprecated no need to use this
   * @since 28.0
   */
  @Deprecated
  public static <V extends @Nullable Object> FluentFuture<V> from(FluentFuture<V> future) {

import java.util.concurrent.Executor;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Hidden superclass of {@link FluentFuture} that provides us a place to declare special GWT
 * versions of the {@link FluentFuture#catching(Class, com.google.common.base.Function)
 * FluentFuture.catching} family of methods. Those versions have slightly different signatures.
 */
@ElementTypesAreNonnullByDefault

import com.google.common.annotations.J2ktIncompatible;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Hidden superclass of {@link FluentFuture} that provides us a place to declare special GWT
 * versions of the {@link FluentFuture#catching(Class, com.google.common.base.Function)
 * FluentFuture.catching} family of methods. Those versions have slightly different signatures.
 */
@GwtCompatible(emulated = true)
@J2ktIncompatible // Super-sourced

    ListenableFuture<String> f = FluentFuture.from(SettableFuture.<String>create());
    assertThat(FluentFuture.from(f)).isSameInstanceAs(f);
  }

  public void testFromNonFluentFuture() throws Exception {
    ListenableFuture<String> f =
        new SimpleForwardingListenableFuture<String>(immediateFuture("a")) {};
    verify(!(f instanceof FluentFuture));
    assertThat(FluentFuture.from(f).get()).isEqualTo("a");

import com.google.common.annotations.J2ktIncompatible;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Hidden superclass of {@link FluentFuture} that provides us a place to declare special GWT
 * versions of the {@link FluentFuture#catching(Class, com.google.common.base.Function)
 * FluentFuture.catching} family of methods. Those versions have slightly different signatures.
 */
@GwtCompatible(emulated = true)
@J2ktIncompatible // Super-sourced

import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * {@link FluentFuture} that forwards all calls to a delegate.
 *
 * <h3>Extension</h3>
 *
 * If you want a class like {@code FluentFuture} but with extra methods, we recommend declaring your
 * own subclass of {@link ListenableFuture}, complete with a method like {@link #from} to adapt an

                return closer.eventuallyClose(mockCloseable, executor);
              }
            },
            executor);
    FluentFuture<Closeable> unused = closingFuture.finishToFuture();
    assertThrows(
        IllegalStateException.class,
        () -> {
          FluentFuture<Closeable> unused2 = closingFuture.finishToFuture();
        });
  }

import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * {@link FluentFuture} that forwards all calls to a delegate.
 *
 * <h3>Extension</h3>
 *
 * If you want a class like {@code FluentFuture} but with extra methods, we recommend declaring your
 * own subclass of {@link ListenableFuture}, complete with a method like {@link #from} to adapt an

 * Futures#transform(ListenableFuture, com.google.common.base.Function, Executor) Futures.transform}
 * (or {@link FluentFuture#transform(com.google.common.base.Function, Executor)
 * FluentFuture.transform}), but you will often find it easier to use a framework. Frameworks
 * automate the process, often adding features like monitoring, debugging, and cancellation.

              public Closeable call(DeferredCloser closer) throws Exception {
                return closer.eventuallyClose(mockCloseable, executor);
              }
            },
            executor);
    FluentFuture<Closeable> unused = closingFuture.finishToFuture();
    assertThrows(
        IllegalStateException.class,
        () ->
            closingFuture.finishToValueAndCloser(