Simplify GuardedCall and default its return type to void

src/AudacityException.h

@@ -18,6 +18,7 @@
 
 #include "MemoryX.h"
 #include <wx/app.h>
+#include <exception>
 
 #include "Internat.h"
 
@@ -105,29 +106,6 @@ struct DefaultDelayedHandlerAction
    }
 };
 
-// Helpers for defining GuardedCall:
-
-// Call one function object,
-// then another unless the first throws, return result of first
-template <typename R> struct Sequencer {
-   template <typename F1, typename Argument, typename F2>
-   R operator () (const F1 &f1, Argument &&a, const F2 &f2)
-   {
-      auto result = f1( std::forward<Argument>(a) );
-      f2();
-      return result;
-   }
-};
-// template specialization to allow R to be void
-template <> struct Sequencer<void> {
-   template <typename F1, typename Argument, typename F2>
-   void operator () (const F1 &f1, Argument &&a, const F2 &f2)
-   {
-      f1( std::forward<Argument>(a) );
-      f2();
-   }
-};
-
 // Classes that can supply the second argument of GuardedCall:
 // Frequently useful converter of all exceptions to some failure constant
 template <typename R> struct SimpleGuard
@@ -169,11 +147,11 @@ inline SimpleGuard< void > MakeSimpleGuard() { return {}; }
  * for the guarded call or throw the same or another exception.
  * It executes in the same thread as the body.
  *
- * If the handler catches non-null and does not throw, then delayedHandler
+ * If the handler is passed non-null and does not throw, then delayedHandler
  * executes later in the main thread, in idle time of the event loop.
  */
 template <
-   typename R, // return type
+   typename R = void, // return type
 
    typename F1, // function object with signature R()
 
@@ -190,15 +168,18 @@ R GuardedCall
 {
    try { return body(); }
    catch ( AudacityException &e ) {
-      return Sequencer<R>{}( handler, &e,
-         [&] {
+
+      auto end = finally([&]{
+         if (!std::uncaught_exception()) {
             auto pException =
                std::shared_ptr< AudacityException > { e.Move().release() };
             wxTheApp->CallAfter( [=] { // capture pException by value
                delayedHandler( pException.get() );
             } );
          }
-      );
+      });
+
+      return handler( &e );
    }
    catch ( ... ) {
       return handler( nullptr );

src/AudioIO.cpp

@@ -2724,7 +2724,7 @@ void AudioIO::StopStream()
 
             // If the other track operations fail their strong guarantees, then
             // the shift for latency correction may be skipped.
-            GuardedCall<void>( [&] {
+            GuardedCall( [&] {
                WaveTrack* track = mCaptureTracks[i].get();
 
                // use NOFAIL-GUARANTEE that track is flushed,
@@ -3976,7 +3976,7 @@ void AudioIO::FillBuffers()
 
    if (!mRecordingException &&
        mCaptureTracks.size() > 0)
-      GuardedCall<void>( [&] {
+      GuardedCall( [&] {
          // start record buffering
          auto commonlyAvail = GetCommonlyAvailCapture();
 

src/DirManager.cpp

@@ -1660,7 +1660,7 @@ _("Project check of \"%s\" folder \
                   // and don't try to recover other files but
                   // silence them too.  GuardedCall will cause an appropriate
                   // error message for the user.
-                  GuardedCall<void>(
+                  GuardedCall(
                      [&] { ab->Recover(); },
                      [&] (AudacityException*) { action = 1; }
                   );
@@ -1726,7 +1726,7 @@ _("Project check of \"%s\" folder \
                   // and don't try to recover other files but
                   // silence them too.  GuardedCall will cause an appropriate
                   // error message for the user.
-                  GuardedCall<void>(
+                  GuardedCall(
                      [&] {
                         b->Recover();
                         nResult |= FSCKstatus_CHANGED;
@@ -1800,7 +1800,7 @@ _("Project check of \"%s\" folder \
                   // and don't try to recover other files but
                   // silence them too.  GuardedCall will cause an appropriate
                   // error message for the user.
-                  GuardedCall<void>(
+                  GuardedCall(
                      [&] {
                         //regenerate with zeroes
                         b->Recover();

src/Project.cpp

@@ -502,7 +502,7 @@ bool ImportXMLTagHandler::HandleXMLTag(const wxChar *tag, const wxChar **attrs)
 
    // Guard this call so that C++ exceptions don't propagate through
    // the expat library
-   GuardedCall< void >(
+   GuardedCall(
       [&] { mProject->Import(strAttr, &trackArray); },
       [&] (AudacityException*) { trackArray.clear(); }
    );

src/Tags.cpp

@@ -1239,7 +1239,7 @@ void TagsEditor::OnSave(wxCommandEvent & WXUNUSED(event))
       return;
    }
 
-   GuardedCall< void >( [&] {
+   GuardedCall( [&] {
       // Create/Open the file
       XMLFileWriter writer{ fn, _("Error Saving Tags File") };
 

src/effects/Effect.cpp

@@ -2513,7 +2513,7 @@ void Effect::Preview(bool dryOnly)
       // was called.
       if (!dryOnly) {
          End();
-         GuardedCall< void >( [&]{ Init(); } );
+         GuardedCall( [&]{ Init(); } );
       }
 
       if (FocusDialog) {

src/effects/Equalization.cpp

@@ -1600,7 +1600,7 @@ void EffectEqualization::SaveCurves(const wxString &fileName)
    else
       fn = fileName;
 
-   GuardedCall< void >( [&] {
+   GuardedCall( [&] {
       // Create/Open the file
       const wxString fullPath{ fn.GetFullPath() };
       XMLFileWriter eqFile{ fullPath, _("Error Saving Equalization Curves") };

src/export/ExportFFmpegDialogs.cpp

@@ -494,7 +494,7 @@ FFmpegPresets::FFmpegPresets()
 FFmpegPresets::~FFmpegPresets()
 {
    // We're in a destructor!  Don't let exceptions out!
-   GuardedCall< void >( [&] {
+   GuardedCall( [&] {
       wxFileName xmlFileName{ FileNames::DataDir(), wxT("ffmpeg_presets.xml") };
       XMLFileWriter writer{
          xmlFileName.GetFullPath(), _("Error Saving FFmpeg Presets") };
@@ -520,7 +520,7 @@ void FFmpegPresets::ImportPresets(wxString &filename)
 
 void FFmpegPresets::ExportPresets(wxString &filename)
 {
-   GuardedCall< void >( [&] {
+   GuardedCall( [&] {
       XMLFileWriter writer{ filename, _("Error Saving FFmpeg Presets") };
       WriteXMLHeader(writer);
       WriteXML(writer);

src/export/ExportMultiple.cpp

@@ -585,7 +585,7 @@ void ExportMultiple::OnExport(wxCommandEvent& WXUNUSED(event))
          FileList += '\n';
       }
 
-      GuardedCall<void>( [&] {
+      GuardedCall( [&] {
          // This results dialog is a child of this dialog.
          HelpSystem::ShowInfoDialog( this,
                                     _("Export Multiple"),

src/prefs/KeyConfigPrefs.cpp

@@ -377,7 +377,7 @@ void KeyConfigPrefs::OnExport(wxCommandEvent & WXUNUSED(event))
       return;
    }
 
-   GuardedCall< void >( [&] {
+   GuardedCall( [&] {
       XMLFileWriter prefFile{ file, _("Error Exporting Keyboard Shortcuts") };
       mManager->WriteXML(prefFile);
       prefFile.Commit();

src/xml/XMLWriter.cpp

@@ -329,7 +329,7 @@ XMLFileWriter::XMLFileWriter
 XMLFileWriter::~XMLFileWriter()
 {
    // Don't let a destructor throw!
-   GuardedCall< void >( [&] {
+   GuardedCall( [&] {
       if (!mCommitted) {
          auto fileName = GetName();
          if ( IsOpened() )