libgfx: Add SafeLog

/*

 * Copyright 2016 The Android Open Source Project

 *

 * Licensed under the Apache License, Version 2.0 (the "License");

 * you may not use this file except in compliance with the License.

 * You may obtain a copy of the License at

 *

 *      http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

#pragma once

#pragma clang diagnostic push

#pragma clang diagnostic ignored "-Weverything"

#include <fmt/format.h>

#include <log/log.h>

#pragma clang diagnostic pop

#include <type_traits>

namespace android {

namespace gfx {

/* SafeLog is a mix-in that can be used to easily add typesafe logging using fmtlib to any class.

 * To use it, inherit from it using CRTP and implement the getLogTag method.

 *

 * For example:

 *

 * class Frobnicator : private SafeLog<Frobnicator> {

 *     friend class SafeLog<Frobnicator>;  // Allows getLogTag to be private

 *

 *   public:

 *     void frobnicate(int32_t i);

 *

 *   private:

 *     // SafeLog does member access on the object calling alog*, so this tag can theoretically vary

 *     // by instance unless getLogTag is made static

 *     const char* getLogTag() { return "Frobnicator"; }

 * };

 *

 * void Frobnicator::frobnicate(int32_t i) {

 *     // Logs something like "04-16 21:35:46.811  3513  3513 I Frobnicator: frobnicating 42"

 *     alogi("frobnicating {}", i);

 * }

 *

 * See http://fmtlib.net for more information on the formatting API.

 */

template <typename T>

class SafeLog {

  protected:

    template <typename... Args>

#if LOG_NDEBUG

    void alogv(Args&&... /*unused*/) const {

    }

#else

    void alogv(Args&&... args) const {

        alog<ANDROID_LOG_VERBOSE>(std::forward<Args>(args)...);

    }

#endif

    template <typename... Args>

    void alogd(Args&&... args) const {

        alog<ANDROID_LOG_DEBUG>(std::forward<Args>(args)...);

    }

    template <typename... Args>

    void alogi(Args&&... args) const {

        alog<ANDROID_LOG_INFO>(std::forward<Args>(args)...);

    }

    template <typename... Args>

    void alogw(Args&&... args) const {

        alog<ANDROID_LOG_WARN>(std::forward<Args>(args)...);

    }

    template <typename... Args>

    void aloge(Args&&... args) const {

        alog<ANDROID_LOG_ERROR>(std::forward<Args>(args)...);

    }

  private:

    // Suppresses clang-tidy check cppcoreguidelines-pro-bounds-array-to-pointer-decay

    template <size_t strlen, typename... Args>

    void write(fmt::MemoryWriter* writer, const char (&str)[strlen], Args&&... args) const {

        writer->write(static_cast<const char*>(str), std::forward<Args>(args)...);

    }

    template <int priority, typename... Args>

    void alog(Args&&... args) const {

        static_assert(std::is_base_of<SafeLog<T>, T>::value, "Can't convert to SafeLog pointer");

        fmt::MemoryWriter writer;

        write(&writer, std::forward<Args>(args)...);

        auto derivedThis = static_cast<const T*>(this);

        android_writeLog(priority, derivedThis->getLogTag(), writer.c_str());

    }

};

}  // namespace gfx

}  // namespace android