honor some cppcheck recommendations (#5817)

arangod/Aql/Query.h

@@ -317,14 +317,14 @@ class Query {
 
   /// @brief setter for the continue callback:
   ///        We can either have a handler or a callback
-  void setContinueCallback(std::function<void()> cb) {
+  void setContinueCallback(std::function<void()> const& cb) {
     _continueCallback = cb;
     _hasHandler = false;
   }
 
   /// @brief setter for the continue handler:
   ///        We can either have a handler or a callback
-  void setContinueHandler(std::function<void()> handler) {
+  void setContinueHandler(std::function<void()> const& handler) {
     _continueCallback = handler;
     _hasHandler = true;
   }

arangod/Aql/RestAqlHandler.cpp

@@ -703,10 +703,8 @@ RestStatus RestAqlHandler::handleUseQuery(std::string const& operation, Query* q
       VPackObjectBuilder guard(&answerBuilder);
       if (operation == "lock") {
         // Mark current thread as potentially blocking:
-        int res = TRI_ERROR_INTERNAL;
+        int res = query->trx()->lockCollections();
-
         // let exceptions propagate from here
-        res = query->trx()->lockCollections();
 
         answerBuilder.add(StaticStrings::Error, VPackValue(res != TRI_ERROR_NO_ERROR));
         answerBuilder.add(StaticStrings::Code, VPackValue(res));

arangod/Scheduler/Scheduler.cpp

@@ -208,7 +208,7 @@ Scheduler::~Scheduler() {
 }
 
 // do not pass callback by reference, might get deleted before execution
-void Scheduler::post(std::function<void()> const callback) {
+void Scheduler::post(std::function<void()> const& callback) {
   incQueued();
 
   try {
@@ -229,7 +229,7 @@ void Scheduler::post(std::function<void()> const callback) {
 
 // do not pass callback by reference, might get deleted before execution
 void Scheduler::post(asio_ns::io_context::strand& strand,
-                     std::function<void()> const callback) {
+                     std::function<void()> const& callback) {
   incQueued();
 
   try {
@@ -341,7 +341,7 @@ bool Scheduler::pushToFifo(size_t fifo, std::function<void()> const& callback) {
   size_t p = fifo - 1;
   TRI_ASSERT(0 < fifo && p < NUMBER_FIFOS);
 
-  std::unique_ptr<FifoJob> job(new FifoJob(callback));
+  auto job = std::make_unique<FifoJob>(callback);
 
   try {
     if (0 < _maxFifoSize[p] && (int64_t)_maxFifoSize[p] <= _fifoSize[p]) {

arangod/Scheduler/Scheduler.h

@@ -91,9 +91,9 @@ class Scheduler {
     uint64_t _queued;
   };
 
-  void post(std::function<void()> const callback);
+  void post(std::function<void()> const& callback);
   void post(asio_ns::io_context::strand&,
-            std::function<void()> const callback);
+            std::function<void()> const& callback);
 
   bool queue(RequestPriority prio, std::function<void()> const&);
   void drain();
@@ -175,7 +175,7 @@ class Scheduler {
   // queue is full
 
   struct FifoJob {
-    FifoJob(std::function<void()> const& callback) : _callback(callback) {}
+    explicit FifoJob(std::function<void()> const& callback) : _callback(callback) {}
     std::function<void()> _callback;
   };