Merge "libbinder: simpler scope_guard implementation" into main

#pragma once

#include <functional>

#include <memory>

#include <optional>

namespace android::binder::impl {

template <typename F>

class scope_guard;

template <typename F>

scope_guard<F> make_scope_guard(F f);

template <typename F>

class scope_guard {

public:

    inline ~scope_guard() {

        if (f_.has_value()) std::move(f_.value())();

    }

    inline void release() { f_.reset(); }

private:

    friend scope_guard<F> android::binder::impl::make_scope_guard(F);

    inline scope_guard(F&& f) : f_(std::move(f)) {}

    std::optional<F> f_;

};

template <typename F>

inline scope_guard<F> make_scope_guard(F f) {

    return scope_guard<F>(std::move(f));

}

template <typename F>

constexpr void assert_small_callable() {

    // While this buffer (std::function::__func::__buf_) is an implementation detail generally not

                  "Try using std::ref, but make sure lambda lives long enough to be called.");

}

template <typename F>

std::unique_ptr<void, std::function<void(void*)>> make_scope_guard(F&& f) {

    assert_small_callable<decltype(std::bind(f))>();

    return {reinterpret_cast<void*>(true), std::bind(f)};

}

template <typename T>

class SmallFunction : public std::function<T> {

public: