New argument for ProjectManager::OpenProject, not yet implemented...

... It is false in exactly the cases where there is now also a check first for
the safety of opening a project file.

Those are the cases where a new project was made for imports, but this was not
necessary for safety.  Yet old behavior will be preserved in such cases.

src/AudacityApp.cpp

@@ -815,7 +815,8 @@ bool AudacityApp::MRUOpen(const FilePath &fullPathStr) {
 
          if (proj && !ProjectManager::SafeToOpenProjectInto(*proj))
             proj = nullptr;
-         ( void ) ProjectManager::OpenProject( proj, fullPathStr );
+         ( void ) ProjectManager::OpenProject( proj, fullPathStr,
+               true /* addtohistory */, false /* reuseNonemptyProject */ );
       }
       else {
          // File doesn't exist - remove file from history

src/AutoRecoveryDialog.cpp

@@ -430,7 +430,7 @@ static bool RecoverAllProjects(const FilePaths &files,
       std::swap(proj, pproj);
 
       // Open project.
-      if (ProjectManager::OpenProject(proj, file, false) == nullptr)
+      if (ProjectManager::OpenProject(proj, file, false, true) == nullptr)
       {
          return false;
       }

src/ProjectManager.cpp

@@ -873,7 +873,8 @@ void ProjectManager::OpenFiles(AudacityProject *proj)
 
       if (proj && !SafeToOpenProjectInto(*proj))
          proj = nullptr;
-      proj = OpenProject( proj, fileName );
+      proj = OpenProject( proj, fileName,
+         true /* addtohistory */, false /* reuseNonemptyProject */ );
    }
 }
 
@@ -901,7 +902,8 @@ bool ProjectManager::SafeToOpenProjectInto(AudacityProject &proj)
 }
 
 AudacityProject *ProjectManager::OpenProject(
-   AudacityProject *pProject, const FilePath &fileNameArg, bool addtohistory)
+   AudacityProject *pProject, const FilePath &fileNameArg,
+   bool addtohistory, bool)
 {
    bool success = false;
    AudacityProject *pNewProject = nullptr;

src/ProjectManager.h

@@ -48,12 +48,18 @@ public:
    //! False when it is unsafe to overwrite proj with contents of an .aup3 file
    static bool SafeToOpenProjectInto(AudacityProject &proj);
 
-   // Return the given project if that is not NULL, else create a project.
-   // Then open the given project path.
-   // But if an exception escapes this function, create no NEW project.
+   //! Open a file into an AudacityProject, returning the project, or nullptr for failure
+   /*!
+    If an exception escapes this function, no projects are created.
+    @param pProject if not null, a project that may be reused
+    @param fileNameArg path to the file to open; not always an Audacity project file, may be an import
+    @param addtohistory whether to add .aup3 files to the MRU list (but always done for imports)
+    @param reuseNonemptyProject if true, may reuse the given project when nonempty,
+       but only if importing (not for a project file)
+    */
    static AudacityProject *OpenProject(
       AudacityProject *pProject,
-      const FilePath &fileNameArg, bool addtohistory = true);
+      const FilePath &fileNameArg, bool addtohistory, bool reuseNonemptyProject);
 
    void ResetProjectToEmpty();
 

src/import/ImportLOF.cpp

@@ -410,7 +410,8 @@ void LOFImportFileHandle::lofOpenFiles(wxString* ln)
           * audio file. TODO: Some sort of message here? */
 
 #endif // USE_MIDI
-         mProject = ProjectManager::OpenProject( mProject, targetfile );
+         mProject = ProjectManager::OpenProject( mProject, targetfile,
+            true /* addtohistory */, true /* reuseNonemptyProject */ );
 
       // Set tok to right after filename
       temptok2.SetString(targettoken);