Don't create placeholder clips in Duplicate command ...

... when there is no clip at the right edge of the selection.

src/LabelTrack.cpp

@@ -2361,7 +2361,7 @@ Track::Holder LabelTrack::SplitCut(double t0, double t1)
 }
 #endif
 
-Track::Holder LabelTrack::Copy(double t0, double t1) const
+Track::Holder LabelTrack::Copy(double t0, double t1, bool) const
 {
    auto tmp = std::make_unique<LabelTrack>(GetDirManager());
    const auto lt = static_cast<LabelTrack*>(tmp.get());

src/LabelTrack.h

@@ -155,11 +155,7 @@ class AUDACITY_DLL_API LabelTrack final : public Track
 #endif
 
    Track::Holder Cut  (double t0, double t1) override;
-   // JKC Do not add the const modifier to Copy(), Clear()
+   Track::Holder Copy (double t0, double t1, bool forClipboard = true) const override;
-   // or Paste() because then it
-   // is no longer recognised as a virtual function matching the
-   // one in Track.
-   Track::Holder Copy (double t0, double t1) const override;
    bool Clear(double t0, double t1) override;
    bool Paste(double t, const Track * src) override;
    bool Repeat(double t0, double t1, int n);

src/Menus.cpp

@@ -4789,8 +4789,9 @@ void AudacityProject::OnDuplicate()
 
    while (n) {
       if (n->GetSelected()) {
+         // Make copies not for clipboard but for direct addition to the project
          auto dest = n->Copy(mViewInfo.selectedRegion.t0(),
-                 mViewInfo.selectedRegion.t1());
+                 mViewInfo.selectedRegion.t1(), false);
          if (dest) {
             dest->Init(*n);
             dest->SetOffset(wxMax(mViewInfo.selectedRegion.t0(), n->GetOffset()));

src/NoteTrack.cpp

@@ -454,7 +454,7 @@ Track::Holder NoteTrack::Cut(double t0, double t1)
    return std::move(newTrack);
 }
 
-Track::Holder NoteTrack::Copy(double t0, double t1) const
+Track::Holder NoteTrack::Copy(double t0, double t1, bool) const
 {
    if (t1 <= t0)
       return{};

src/NoteTrack.h

@@ -91,7 +91,7 @@ class AUDACITY_DLL_API NoteTrack final : public Track {
 
    // High-level editing
    Track::Holder Cut  (double t0, double t1) override;
-   Track::Holder Copy (double t0, double t1) const override;
+   Track::Holder Copy (double t0, double t1, bool forClipboard = true) const override;
    bool Trim (double t0, double t1) /* not override */;
    bool Clear(double t0, double t1) override;
    bool Paste(double t, const Track *src) override;

src/Project.cpp

@@ -4905,6 +4905,7 @@ void AudacityProject::EditClipboardByLabel( EditDestFunction action )
       if( n->GetKind() == Track::Wave && ( allTracks || n->GetSelected() ) )
       {
          WaveTrack *wt = ( WaveTrack* )n;
+         // This track accumulates the needed clips, right to left:
          Track::Holder merged;
          for( int i = (int)regions.size() - 1; i >= 0; i-- )
          {
@@ -4923,6 +4924,11 @@ void AudacityProject::EditClipboardByLabel( EditDestFunction action )
                      merged->Offset(
                         regions.at(i + 1).start - region.end);
 
+                  // dest may have a placeholder clip at the end that is
+                  // removed when pasting, which is okay because we proceed
+                  // right to left.  Any placeholder already in merged is kept.
+                  // Only the rightmost placeholder is important in the final
+                  // result.
                   bool bResult = merged->Paste( 0.0 , dest.get() );
                   wxASSERT(bResult); // TO DO: Actually handle this.
                   wxUnusedVar(bResult);

src/Track.h

@@ -216,7 +216,11 @@ class AUDACITY_DLL_API Track /* not final */ : public XMLTagHandler
    virtual Holder Cut(double WXUNUSED(t0), double WXUNUSED(t1)) { return{}; }
 
    // Create a NEW track and don't modify this track (or return null for failure)
-   virtual Holder Copy(double WXUNUSED(t0), double WXUNUSED(t1)) const { return{}; }
+   // Note that subclasses may want to distinguish tracks stored in a clipboard
+   // from those stored in a project
+   virtual Holder Copy
+      (double WXUNUSED(t0), double WXUNUSED(t1), bool forClipboard = true) const
+   { return{}; }
 
    // Return true for success
    virtual bool Clear(double WXUNUSED(t0), double WXUNUSED(t1)) {return false;}

src/WaveTrack.cpp

@@ -630,7 +630,7 @@ bool WaveTrack::Trim (double t0, double t1)
 
 
 
-Track::Holder WaveTrack::Copy(double t0, double t1) const
+Track::Holder WaveTrack::Copy(double t0, double t1, bool forClipboard) const
 {
    if (t1 <= t0)
       return{};
@@ -695,7 +695,10 @@ Track::Holder WaveTrack::Copy(double t0, double t1) const
 
    // AWD, Oct 2009: If the selection ends in whitespace, create a placeholder
    // clip representing that whitespace
-   if (newTrack->GetEndTime() + 1.0 / newTrack->GetRate() < t1 - t0)
+   // PRL:  Only if we want the track for pasting into other tracks.  Not if it
+   // goes directly into a project as in the Duplicate command.
+   if (forClipboard &&
+       newTrack->GetEndTime() + 1.0 / newTrack->GetRate() < t1 - t0)
    {
       auto placeholder = make_movable<WaveClip>(mDirManager,
             newTrack->GetSampleFormat(),

src/WaveTrack.h

@@ -167,8 +167,14 @@ class AUDACITY_DLL_API WaveTrack final : public Track {
    //
 
    Track::Holder Cut(double t0, double t1) override;
-   Track::Holder Copy(double t0, double t1) const override;
+
+   // If forClipboard is true,
+   // and there is no clip at the end time of the selection, then the result
+   // will contain a "placeholder" clip whose only purpose is to make
+   // GetEndTime() correct.  This clip is not re-copied when pasting.
+   Track::Holder Copy(double t0, double t1, bool forClipboard = true) const override;
    Track::Holder CopyNonconst(double t0, double t1) /* not override */;
+
    bool Clear(double t0, double t1) override;
    bool Paste(double t0, const Track *src) override;
    bool ClearAndPaste(double t0, double t1,