class EagerContext;
class CustomDevice;
class CustomDeviceOpHandler;
class Device;

// LINT.IfChange
// Note: Keep in sync with exported copy of enum in eager/c_api.h.
enum ContextDevicePlacementPolicy {
  // Running operations with input tensors on the wrong device will fail.
  DEVICE_PLACEMENT_EXPLICIT = 0,
  // Copy the tensor to the right device but log a warning.
  DEVICE_PLACEMENT_WARN = 1,

    }
  }
};
}  // namespace internal

using TracingOperationPtr =
    std::unique_ptr<TracingOperation, internal::TracingOperationDeleter>;

// This holds the context for the execution: dispatching operations either to an
// MLIR implementation or to a graph implementation.
class TracingContext : public AbstractContext {
 protected:
  explicit TracingContext(AbstractContextKind kind) : AbstractContext(kind) {}

// maintains the map from `op_id` to a `OpTapeEntry` which stores the `op_type`,
// inputs and outputs and the gradient function These data structures combined
// allow us to trace the data dependencies between operations and hence compute
// gradients.
//
// `ZerosLike` is not expected to be called and returns a nullptr. The creation
// of default zeros grads is handled by the `DefaultGradientFunction` registered
// for each op.