cleanup: Add const to local variables where possible.

To reproduce:
```
run-clang-tidy \
  -checks="-*,misc-const-correctness" \
  -p _build \
  -fix \
  $(find . -name "*.h" -or -name "*.cpp" | grep -v "/_build/")
```

.clang-tidy

@@ -1,5 +1,6 @@
 Checks: "-*
 , google-explicit-constructor
+, misc-const-correctness
 , modernize-avoid-bind
 , modernize-deprecated-headers
 , modernize-loop-convert

audio/src/backend/alsink.cpp

@@ -16,7 +16,7 @@
 
 AlSink::~AlSink()
 {
-    QMutexLocker<QRecursiveMutex> locker{&killLock};
+    const QMutexLocker<QRecursiveMutex> locker{&killLock};
 
     // unsubscribe only if not already killed
     if (!killed) {
@@ -27,7 +27,7 @@ AlSink::~AlSink()
 
 void AlSink::playAudioBuffer(const int16_t* data, int samples, unsigned channels, int sampleRate) const
 {
-    QMutexLocker<QRecursiveMutex> locker{&killLock};
+    const QMutexLocker<QRecursiveMutex> locker{&killLock};
 
     if (killed) {
         qCritical() << "Trying to play audio on an invalid sink";
@@ -38,7 +38,7 @@ void AlSink::playAudioBuffer(const int16_t* data, int samples, unsigned channels
 
 void AlSink::playMono16Sound(const IAudioSink::Sound& sound)
 {
-    QMutexLocker<QRecursiveMutex> locker{&killLock};
+    const QMutexLocker<QRecursiveMutex> locker{&killLock};
 
     if (killed) {
         qCritical() << "Trying to play sound on an invalid sink";
@@ -49,7 +49,7 @@ void AlSink::playMono16Sound(const IAudioSink::Sound& sound)
 
 void AlSink::startLoop()
 {
-    QMutexLocker<QRecursiveMutex> locker{&killLock};
+    const QMutexLocker<QRecursiveMutex> locker{&killLock};
 
     if (killed) {
         qCritical() << "Trying to start loop on an invalid sink";
@@ -60,7 +60,7 @@ void AlSink::startLoop()
 
 void AlSink::stopLoop()
 {
-    QMutexLocker<QRecursiveMutex> locker{&killLock};
+    const QMutexLocker<QRecursiveMutex> locker{&killLock};
 
     if (killed) {
         qCritical() << "Trying to stop loop on an invalid sink";
@@ -71,7 +71,7 @@ void AlSink::stopLoop()
 
 uint AlSink::getSourceId() const
 {
-    uint tmp = sourceId;
+    const uint tmp = sourceId;
     return tmp;
 }
 
@@ -92,7 +92,7 @@ AlSink::AlSink(OpenAL& al, uint sourceId_)
 
 AlSink::operator bool() const
 {
-    QMutexLocker<QRecursiveMutex> locker{&killLock};
+    const QMutexLocker<QRecursiveMutex> locker{&killLock};
 
     return !killed;
 }

audio/src/backend/alsource.cpp

@@ -21,7 +21,7 @@ AlSource::AlSource(OpenAL& al)
 
 AlSource::~AlSource()
 {
-    QMutexLocker<QRecursiveMutex> locker{&killLock};
+    const QMutexLocker<QRecursiveMutex> locker{&killLock};
 
     // unsubscribe only if not already killed
     if (!killed) {
@@ -32,7 +32,7 @@ AlSource::~AlSource()
 
 AlSource::operator bool() const
 {
-    QMutexLocker<QRecursiveMutex> locker{&killLock};
+    const QMutexLocker<QRecursiveMutex> locker{&killLock};
     return !killed;
 }
 

audio/src/backend/openal.cpp

@@ -160,7 +160,7 @@ void OpenAL::checkAlcError(ALCdevice* device) noexcept
  */
 void OpenAL::setOutputVolume(qreal volume)
 {
-    QMutexLocker<QRecursiveMutex> locker(&audioLock);
+    const QMutexLocker<QRecursiveMutex> locker(&audioLock);
 
     alListenerf(AL_GAIN, static_cast<ALfloat>(std::max(0.0, std::min(volume, 1.0))));
     checkAlError();
@@ -173,7 +173,7 @@ void OpenAL::setOutputVolume(qreal volume)
  */
 qreal OpenAL::minInputGain() const
 {
-    QMutexLocker<QRecursiveMutex> locker(&audioLock);
+    const QMutexLocker<QRecursiveMutex> locker(&audioLock);
     return minInGain;
 }
 
@@ -184,7 +184,7 @@ qreal OpenAL::minInputGain() const
  */
 qreal OpenAL::maxInputGain() const
 {
-    QMutexLocker<QRecursiveMutex> locker(&audioLock);
+    const QMutexLocker<QRecursiveMutex> locker(&audioLock);
     return maxInGain;
 }
 
@@ -195,7 +195,7 @@ qreal OpenAL::maxInputGain() const
  */
 qreal OpenAL::minInputThreshold() const
 {
-    QMutexLocker<QRecursiveMutex> locker(&audioLock);
+    const QMutexLocker<QRecursiveMutex> locker(&audioLock);
     return minInThreshold;
 }
 
@@ -206,7 +206,7 @@ qreal OpenAL::minInputThreshold() const
  */
 qreal OpenAL::maxInputThreshold() const
 {
-    QMutexLocker<QRecursiveMutex> locker(&audioLock);
+    const QMutexLocker<QRecursiveMutex> locker(&audioLock);
     return maxInThreshold;
 }
 
@@ -255,7 +255,7 @@ bool OpenAL::reinitOutput(const QString& outDevDesc)
  */
 std::unique_ptr<IAudioSink> OpenAL::makeSink()
 {
-    QMutexLocker<QRecursiveMutex> locker(&audioLock);
+    const QMutexLocker<QRecursiveMutex> locker(&audioLock);
 
     if (!autoInitOutput()) {
         qWarning("Failed to subscribe to audio output device.");
@@ -283,7 +283,7 @@ std::unique_ptr<IAudioSink> OpenAL::makeSink()
  */
 void OpenAL::destroySink(AlSink& sink)
 {
-    QMutexLocker<QRecursiveMutex> locker(&audioLock);
+    const QMutexLocker<QRecursiveMutex> locker(&audioLock);
 
     const auto sinksErased = sinks.erase(&sink);
     const auto soundSinksErased = soundSinks.erase(&sink);
@@ -316,7 +316,7 @@ void OpenAL::destroySink(AlSink& sink)
  */
 std::unique_ptr<IAudioSource> OpenAL::makeSource()
 {
-    QMutexLocker<QRecursiveMutex> locker(&audioLock);
+    const QMutexLocker<QRecursiveMutex> locker(&audioLock);
 
     if (!autoInitInput()) {
         qWarning("Failed to subscribe to audio input device.");
@@ -339,7 +339,7 @@ std::unique_ptr<IAudioSource> OpenAL::makeSource()
  */
 void OpenAL::destroySource(AlSource& source)
 {
-    QMutexLocker<QRecursiveMutex> locker(&audioLock);
+    const QMutexLocker<QRecursiveMutex> locker(&audioLock);
 
     const auto s = sources.find(&source);
     if (s == sources.end()) {
@@ -393,7 +393,7 @@ bool OpenAL::initInput(const QString& deviceName, uint32_t channels)
 
     // TODO: Try to actually detect if our audio source is stereo
     inputChannels = channels;
-    int stereoFlag = inputChannels == 1 ? AL_FORMAT_MONO16 : AL_FORMAT_STEREO16;
+    const int stereoFlag = inputChannels == 1 ? AL_FORMAT_MONO16 : AL_FORMAT_STEREO16;
     const int bytesPerSample = 2;
     const int safetyFactor = 2; // internal OpenAL ring buffer. must be larger than our inputBuffer
                                 // to avoid the ring from overwriting itself between captures.
@@ -480,7 +480,7 @@ void OpenAL::playMono16Sound(AlSink& sink, const IAudioSink::Sound& sound)
         return;
     }
 
-    QMutexLocker<QRecursiveMutex> locker(&audioLock);
+    const QMutexLocker<QRecursiveMutex> locker(&audioLock);
 
     // interrupt possibly playing sound, we don't buffer here
     alSourceStop(sourceId);
@@ -508,12 +508,12 @@ void OpenAL::playMono16Sound(AlSink& sink, const IAudioSink::Sound& sound)
 
 void OpenAL::cleanupSound()
 {
-    QMutexLocker<QRecursiveMutex> locker(&audioLock);
+    const QMutexLocker<QRecursiveMutex> locker(&audioLock);
 
     auto sinkIt = soundSinks.begin();
     while (sinkIt != soundSinks.end()) {
         auto sink = *sinkIt;
-        ALuint sourceId = sink->getSourceId();
+        const ALuint sourceId = sink->getSourceId();
         ALint state = 0;
 
         alGetSourcei(sourceId, AL_SOURCE_STATE, &state);
@@ -530,7 +530,7 @@ void OpenAL::playAudioBuffer(uint sourceId, const int16_t* data, int samples, un
                              int sampleRate)
 {
     assert(channels == 1 || channels == 2);
-    QMutexLocker<QRecursiveMutex> locker(&audioLock);
+    const QMutexLocker<QRecursiveMutex> locker(&audioLock);
 
     if (!(alOutDev && outputInitialized))
         return;
@@ -688,7 +688,7 @@ void OpenAL::doOutput()
  */
 void OpenAL::doAudio()
 {
-    QMutexLocker<QRecursiveMutex> lock(&audioLock);
+    const QMutexLocker<QRecursiveMutex> lock(&audioLock);
 
     // Output section does nothing
 
@@ -708,7 +708,7 @@ void OpenAL::captureSamples(ALCdevice* device, int16_t* buffer, ALCsizei samples
  */
 bool OpenAL::isOutputReady() const
 {
-    QMutexLocker<QRecursiveMutex> locker(&audioLock);
+    const QMutexLocker<QRecursiveMutex> locker(&audioLock);
     return alOutDev && outputInitialized;
 }
 
@@ -767,13 +767,13 @@ void OpenAL::cleanupBuffers(uint sourceId)
 
 void OpenAL::startLoop(uint sourceId)
 {
-    QMutexLocker<QRecursiveMutex> locker(&audioLock);
+    const QMutexLocker<QRecursiveMutex> locker(&audioLock);
     alSourcei(sourceId, AL_LOOPING, AL_TRUE);
 }
 
 void OpenAL::stopLoop(uint sourceId)
 {
-    QMutexLocker<QRecursiveMutex> locker(&audioLock);
+    const QMutexLocker<QRecursiveMutex> locker(&audioLock);
     alSourcei(sourceId, AL_LOOPING, AL_FALSE);
     alSourceStop(sourceId);
     cleanupBuffers(sourceId);

src/appmanager.cpp

@@ -112,7 +112,7 @@ void logMessageHandler(QtMsgType type, const QMessageLogContext& ctxt, const QSt
     }
 
     // Time should be in UTC to save user privacy on log sharing
-    QTime time = QDateTime::currentDateTime().toUTC().time();
+    const QTime time = QDateTime::currentDateTime().toUTC().time();
     QString logPrefix =
         QStringLiteral("[%1 UTC] (%2) %3:%4 : ")
             .arg(time.toString("HH:mm:ss.zzz"), category, file, QString::number(ctxt.line));
@@ -156,8 +156,9 @@ void logMessageHandler(QtMsgType type, const QMessageLogContext& ctxt, const QSt
         logBufferMutex->lock();
         if (logBuffer) {
             // empty logBuffer to file
-            foreach (QByteArray bufferedMsg, *logBuffer)
+            for (const QByteArray& bufferedMsg : *logBuffer) {
                 fwrite(bufferedMsg.constData(), 1, bufferedMsg.size(), logFilePtr);
+            }
 
             delete logBuffer; // no longer needed
             logBuffer = nullptr;
@@ -209,10 +210,10 @@ int AppManager::startGui(QCommandLineParser& parser)
     }
 
 #ifdef LOG_TO_FILE
-    QString logFileDir = settings->getPaths().getAppCacheDirPath();
+    const QString logFileDir = settings->getPaths().getAppCacheDirPath();
     QDir(logFileDir).mkpath(".");
 
-    QString logfile = logFileDir + "qtox.log";
+    const QString logfile = logFileDir + "qtox.log";
     FILE* mainLogFilePtr = fopen(logfile.toLocal8Bit().constData(), "a");
 
     // Trim log file if over 1MB
@@ -295,7 +296,7 @@ int AppManager::startGui(QCommandLineParser& parser)
     }
 
     if (doIpc && !ipc->isCurrentOwner()) {
-        time_t event = ipc->postEvent(eventType, firstParam.toUtf8(), ipcDest);
+        const time_t event = ipc->postEvent(eventType, firstParam.toUtf8(), ipcDest);
         // If someone else processed it, we're done here, no need to actually start qTox
         if (ipc->waitUntilAccepted(event, 2)) {
             if (eventType == "activate") {
@@ -335,7 +336,7 @@ int AppManager::startGui(QCommandLineParser& parser)
         nexus->bootstrapWithProfile(profile);
     } else {
         nexus->setParser(&parser);
-        int returnval = nexus->showLogin(profileName);
+        const int returnval = nexus->showLogin(profileName);
         if (returnval == QDialog::Rejected) {
             return -1;
         }
@@ -394,7 +395,7 @@ int AppManager::run()
         qWarning() << "Couldn't load font";
     }
 
-    QString locale = settings->getTranslation();
+    const QString locale = settings->getTranslation();
     // We need to init the resources in the translations_library explicitly.
     // See https://doc.qt.io/qt-5/resources.html#using-resources-in-a-library
     Q_INIT_RESOURCE(translations);

src/chatlog/chatline.cpp

@@ -166,7 +166,7 @@ void ChatLine::layout(qreal w, QPointF scenePos)
     if (varWidth == 0.0)
         varWidth = 1.0;
 
-    qreal leftover = qMax(0.0, width - fixedWidth);
+    const qreal leftover = qMax(0.0, width - fixedWidth);
 
     qreal maxVOffset = 0.0;
     qreal xOffset = 0.0;
@@ -207,7 +207,7 @@ void ChatLine::layout(qreal w, QPointF scenePos)
     for (int i = 0; i < content.size(); ++i) {
         // calculate vertical alignment
         // vertical alignment may depend on width, so we do it in a second pass
-        qreal yOffset = maxVOffset - content[i]->getAscent();
+        const qreal yOffset = maxVOffset - content[i]->getAscent();
 
         // reposition
         content[i]->setPos(xPos[i], scenePos.y() + yOffset);

src/chatlog/chatmessage.cpp

@@ -58,7 +58,7 @@ ChatMessage::Ptr ChatMessage::createChatMessage(const QString& sender, const QSt
     text = TextFormatter::highlightURI(text);
 
     // text styling
-    Settings::StyleType styleType = settings.getStylePreference();
+    const Settings::StyleType styleType = settings.getStylePreference();
     if (styleType != Settings::StyleType::NONE) {
         text = TextFormatter::applyMarkdown(text, styleType == Settings::StyleType::WITH_CHARS);
     }
@@ -80,14 +80,15 @@ ChatMessage::Ptr ChatMessage::createChatMessage(const QString& sender, const QSt
     }
 
     // Note: Eliding cannot be enabled for RichText items. (QTBUG-17207)
-    QFont baseFont = settings.getChatMessageFont();
+    const QFont baseFont = settings.getChatMessageFont();
     QFont authorFont = baseFont;
     if (isMe)
         authorFont.setBold(true);
 
     QColor color = style.getColor(Style::ColorPalette::MainText);
     if (colorizeName) {
-        QByteArray hash = QCryptographicHash::hash((sender.toUtf8()), QCryptographicHash::Sha256);
+        const QByteArray hash =
+            QCryptographicHash::hash((sender.toUtf8()), QCryptographicHash::Sha256);
         auto lightness = color.lightnessF();
         // Adapt as good as possible to Light/Dark themes
         lightness = lightness * 0.5f + 0.3f;
@@ -134,7 +135,7 @@ ChatMessage::Ptr ChatMessage::createChatInfoMessage(const QString& rawMessage,
                                                     Settings& settings, Style& style)
 {
     ChatMessage::Ptr msg = std::make_shared<ChatMessage>(documentCache, settings, style);
-    QString text = rawMessage.toHtmlEscaped();
+    const QString text = rawMessage.toHtmlEscaped();
 
     QString img;
     switch (type) {
@@ -149,7 +150,7 @@ ChatMessage::Ptr ChatMessage::createChatInfoMessage(const QString& rawMessage,
         break;
     }
 
-    QFont baseFont = settings.getChatMessageFont();
+    const QFont baseFont = settings.getChatMessageFont();
 
     msg->addColumn(new Image(QSize(18, 18), img),
                    ColumnFormat(NAME_COL_WIDTH, ColumnFormat::FixedSize, ColumnFormat::Right));
@@ -170,7 +171,7 @@ ChatMessage::Ptr ChatMessage::createFileTransferMessage(const QString& sender, C
 {
     ChatMessage::Ptr msg = std::make_shared<ChatMessage>(documentCache, settings, style);
 
-    QFont baseFont = settings.getChatMessageFont();
+    const QFont baseFont = settings.getChatMessageFont();
     QFont authorFont = baseFont;
     if (isMe) {
         authorFont.setBold(true);
@@ -194,7 +195,7 @@ ChatMessage::Ptr ChatMessage::createTypingNotification(DocumentCache& documentCa
 {
     ChatMessage::Ptr msg = std::make_shared<ChatMessage>(documentCache, settings, style);
 
-    QFont baseFont = settings.getChatMessageFont();
+    const QFont baseFont = settings.getChatMessageFont();
 
     // Note: "[user]..." is just a placeholder. The actual text is set in
     // ChatForm::setFriendTyping()
@@ -238,7 +239,7 @@ ChatMessage::Ptr ChatMessage::createBusyNotification(DocumentCache& documentCach
 
 void ChatMessage::markAsDelivered(const QDateTime& time)
 {
-    QFont baseFont = settings.getChatMessageFont();
+    const QFont baseFont = settings.getChatMessageFont();
 
     // remove the spinner and replace it by $time
     replaceContent(2, new Timestamp(time, settings.getTimestampFormat(), baseFont, documentCache,