Fix mac build

src/Menus.cpp

@@ -5605,9 +5605,8 @@ void AudacityProject::HandleMixAndRender(bool toNewTrack)
 {
    wxGetApp().SetMissingAliasedFileWarningShouldShow(true);
 
-   auto results =
-      ::MixAndRender(mTracks, mTrackFactory, mRate, mDefaultFormat, 0.0, 0.0);
-   auto &uNewLeft = results.first, &uNewRight = results.second;
+   WaveTrack::Holder uNewLeft, uNewRight;
+   MixAndRender(mTracks, mTrackFactory, mRate, mDefaultFormat, 0.0, 0.0, uNewLeft, uNewRight);
 
    if (uNewLeft) {
       // Remove originals, get stats on what tracks were mixed

src/Mix.cpp

@@ -43,11 +43,13 @@
 #include "float_cast.h"
 
 //TODO-MB: wouldn't it make more sense to DELETE the time track after 'mix and render'?
-std::pair<WaveTrack::Holder, WaveTrack::Holder>
-MixAndRender(TrackList *tracks, TrackFactory *trackFactory,
+void MixAndRender(TrackList *tracks, TrackFactory *trackFactory,
                   double rate, sampleFormat format,
-                  double startTime, double endTime)
+                  double startTime, double endTime,
+                  WaveTrack::Holder &uLeft, WaveTrack::Holder &uRight)
 {
+   uLeft.reset(), uRight.reset();
+
    // This function was formerly known as "Quick Mix".
    Track *t;
    bool mono = false;   /* flag if output can be mono without loosing anything*/
@@ -197,13 +199,11 @@ MixAndRender(TrackList *tracks, TrackFactory *trackFactory,
       mixRight->Flush();
    if (updateResult == eProgressCancelled || updateResult == eProgressFailed)
    {
-      return{};
+      return;
    }
    else {
-      return std::make_pair(
-         std::move(mixLeft),
-         std::move(mixRight)
-      );
+      uLeft = std::move(mixLeft),
+         uRight = std::move(mixRight);
 #if 0
    int elapsedMS = wxGetElapsedTime();
    double elapsedTime = elapsedMS * 0.001;

src/Mix.h

@@ -13,7 +13,6 @@
 #define __AUDACITY_MIX__
 
 #include "MemoryX.h"
-#include <utility>
 #include <wx/string.h>
 
 #include "SampleFormat.h"
@@ -38,12 +37,10 @@ class WaveTrackConstArray;
  * no explicit time range to process, and the whole occupied length of the
  * input tracks is processed.
  */
-std::pair<
-   std::unique_ptr<WaveTrack>,
-   std::unique_ptr<WaveTrack>
-> MixAndRender(TrackList * tracks, TrackFactory *factory,
+void MixAndRender(TrackList * tracks, TrackFactory *factory,
                   double rate, sampleFormat format,
-                  double startTime, double endTime);
+                  double startTime, double endTime,
+                  std::unique_ptr<WaveTrack> &uLeft, std::unique_ptr<WaveTrack> &uRight);
 
 void MixBuffers(int numChannels, int *channelFlags, float *gains,
                 samplePtr src,

src/effects/Effect.cpp

@@ -2569,9 +2569,8 @@ void Effect::Preview(bool dryOnly)
    // Linear Effect preview optimised by pre-mixing to one track.
    // Generators need to generate per track.
    if (mIsLinearEffect && !isGenerator) {
-      auto results = ::MixAndRender(saveTracks, mFactory, rate, floatSample, mT0, t1);
-      auto &mixLeft = results.first;
-      auto &mixRight = results.second;
+      WaveTrack::Holder mixLeft, mixRight;
+      MixAndRender(saveTracks, mFactory, rate, floatSample, mT0, t1, mixLeft, mixRight);
       if (!mixLeft) {
          delete mTracks;
          mTracks = saveTracks;