If exception in cut/copy, leave clipboard clear (no partial results)

src/Menus.cpp

@@ -4149,6 +4149,9 @@ void AudacityProject::OnCut()
    }
 
    ClearClipboard();
+
+   TrackList newClipboard;
+
    n = iter.First();
    while (n) {
       if (n->GetSelected()) {
@@ -4164,11 +4167,17 @@ void AudacityProject::OnCut()
                     mViewInfo.selectedRegion.t1());
 
          if (dest)
-            FinishCopy(n, std::move(dest), *msClipboard);
+            FinishCopy(n, std::move(dest), newClipboard);
       }
       n = iter.Next();
    }
 
+   // Survived possibility of exceptions.  Commit changes to the clipboard now.
+   newClipboard.Swap(*msClipboard);
+
+   // Proceed to change the project.  If this throws, the project will be
+   // rolled back by the top level handler.
+
    n = iter.First();
    while (n) {
       // We clear from selected and sync-lock selected tracks.
@@ -4220,6 +4229,9 @@ void AudacityProject::OnSplitCut()
    Track *n = iter.First();
 
    ClearClipboard();
+
+   TrackList newClipboard;
+
    while (n) {
       if (n->GetSelected()) {
          Track::Holder dest;
@@ -4237,11 +4249,14 @@ void AudacityProject::OnSplitCut()
                        mViewInfo.selectedRegion.t1());
          }
          if (dest)
-            FinishCopy(n, std::move(dest), *msClipboard);
+            FinishCopy(n, std::move(dest), newClipboard);
       }
       n = iter.Next();
    }
 
+   // Survived possibility of exceptions.  Commit changes to the clipboard now.
+   newClipboard.Swap(*msClipboard);
+
    msClipT0 = mViewInfo.selectedRegion.t0();
    msClipT1 = mViewInfo.selectedRegion.t1();
    msClipProject = this;
@@ -4275,17 +4290,23 @@ void AudacityProject::OnCopy()
    }
 
    ClearClipboard();
+
+   TrackList newClipboard;
+
    n = iter.First();
    while (n) {
       if (n->GetSelected()) {
          auto dest = n->Copy(mViewInfo.selectedRegion.t0(),
                  mViewInfo.selectedRegion.t1());
          if (dest)
-            FinishCopy(n, std::move(dest), *msClipboard);
+            FinishCopy(n, std::move(dest), newClipboard);
       }
       n = iter.Next();
    }
 
+   // Survived possibility of exceptions.  Commit changes to the clipboard now.
+   newClipboard.Swap(*msClipboard);
+
    msClipT0 = mViewInfo.selectedRegion.t0();
    msClipT1 = mViewInfo.selectedRegion.t1();
    msClipProject = this;

src/Project.cpp

@@ -4917,6 +4917,9 @@ void AudacityProject::EditClipboardByLabel( EditDestFunction action )
       }
 
    ClearClipboard();
+
+   TrackList newClipboard;
+
    //Apply action on wavetracks starting from
    //labeled regions in the end. This is to correctly perform
    //actions like 'Cut' which collapse the track area.
@@ -4961,10 +4964,13 @@ void AudacityProject::EditClipboardByLabel( EditDestFunction action )
                         regions.at(i + 1).start - region.end);
          }
          if( merged )
-            msClipboard->Add( std::move(merged) );
+            newClipboard.Add( std::move(merged) );
       }
    }
 
+   // Survived possibility of exceptions.  Commit changes to the clipboard now.
+   newClipboard.Swap(*msClipboard);
+
    msClipT0 = regions.front().start;
    msClipT1 = regions.back().end;
 

src/Track.h

@@ -408,6 +408,9 @@ DECLARE_EXPORTED_EVENT_TYPE(AUDACITY_DLL_API, EVT_TRACKLIST_UPDATED, -1);
 
 class TrackList final : public wxEvtHandler, public ListOfTracks
 {
+   // privatize this, make you use Swap instead:
+   using ListOfTracks::swap;
+
  public:
    // Create an empty TrackList
    TrackList();