remove lvalue-qual Future::get(...)

Summary:
This is part of "the great r-valuification of folly::Future":

* This is something we should do for safety in general.
* Using lvalue-qualified `Future::get(...)` has caused some failures around D7840699 since lvalue-qualification hides that operation's move-out semantics - leads to some use of future operations that are really not correct, but are not obviously incorrect.
* Problems with `Future::get(...) &`: it moves-out the result but doesn't invalidate the Future - the Future remains (technically) valid even though it actually is partially moved-out. Callers can subsequently access that moved-out result via things like `future.get()`, `future.result()`, `future.value()`, etc. - these access an already-moved-out result which is/can be surprising.
* Reasons `Future::get(...) &&` is better: its semantics are more obvious and user-testable. It moves-out the Future, leaving it with `future.valid() == false`.
* Note: `get(...)` refers to `get()` and `get(Duration)`.

Reviewed By: yfeldblum

Differential Revision: D8710296

fbshipit-source-id: ae201af1928eb2f6a2897c9b7db884393b36b910

folly/futures/Future-inl.h

@@ -2190,11 +2190,6 @@ T Future<T>::get() && {
   return copy(std::move(*this)).value();
 }
 
-template <class T>
-T Future<T>::get() & {
-  return std::move(wait().value());
-}
-
 template <class T>
 T Future<T>::get(Duration dur) && {
   wait(dur);
@@ -2205,15 +2200,6 @@ T Future<T>::get(Duration dur) && {
   return std::move(future).value();
 }
 
-template <class T>
-T Future<T>::get(Duration dur) & {
-  wait(dur);
-  if (!this->isReady()) {
-    throw_exception<FutureTimeout>();
-  }
-  return std::move(this->value());
-}
-
 template <class T>
 Try<T>& Future<T>::getTry() {
   return result();

folly/futures/Future.h

@@ -1550,13 +1550,6 @@ class Future : private futures::detail::FutureBase<T> {
   /// - `valid() == false`
   T get() &&;
 
-  /// Blocks until the future is fulfilled. Returns the value (moved out), or
-  /// throws the exception. The future must not already have a callback.
-  ///
-  /// Deprecated in favor of `get() &&`.
-  [[deprecated("being removed soon; use rvalue-qualified get() instead")]] T
-  get() &;
-
   /// Blocks until the future is fulfilled, or until `dur` elapses. Returns the
   /// value (moved-out), or throws the exception (which might be a FutureTimeout
   /// exception).
@@ -1570,14 +1563,6 @@ class Future : private futures::detail::FutureBase<T> {
   /// - `valid() == false`
   T get(Duration dur) &&;
 
-  /// Blocks until the future is fulfilled, or until `dur` elapses. Returns the
-  /// value (moved out), or throws the exception (which might be a FutureTimeout
-  /// exception).
-  ///
-  /// Deprecated in favor of `get(Duration) &&`.
-  [[deprecated("being removed soon; use rvalue-qualified get() instead")]] T
-  get(Duration dur) &;
-
   /// A reference to the Try of the value
   ///
   /// Preconditions:

folly/futures/test/FutureTest.cpp

@@ -233,11 +233,6 @@ TEST(Future, hasPreconditionValid) {
 
   DOIT(f.isReady());
   DOIT(f.result());
-  FOLLY_PUSH_WARNING
-  FOLLY_GNU_DISABLE_WARNING("-Wdeprecated-declarations")
-  DOIT(f.get());
-  DOIT(f.get(std::chrono::milliseconds(10)));
-  FOLLY_POP_WARNING
   DOIT(std::move(f).get());
   DOIT(std::move(f).get(std::chrono::milliseconds(10)));
   DOIT(f.getTry());
@@ -272,11 +267,6 @@ TEST(Future, hasPostconditionValid) {
   DOIT(swallow(f.poll()));
   DOIT(f.raise(std::logic_error("foo")));
   DOIT(f.cancel());
-  FOLLY_PUSH_WARNING
-  FOLLY_GNU_DISABLE_WARNING("-Wdeprecated-declarations")
-  DOIT(swallow(f.get()));
-  DOIT(swallow(f.get(std::chrono::milliseconds(10))));
-  FOLLY_POP_WARNING
   DOIT(swallow(f.getTry()));
   DOIT(f.wait());
   DOIT(std::move(f.wait()));