Avoid some wxString copies

src/Project.h

@@ -247,7 +247,7 @@ class AUDACITY_DLL_API AudacityProject final : public wxFrame,
    #endif
    void Clear();
 
-   wxString GetFileName() { return mFileName; }
+   const wxString &GetFileName() { return mFileName; }
    bool GetDirty() { return mDirty; }
    void SetProjectTitle();
 

src/commands/OpenSaveCommands.cpp

@@ -48,9 +48,9 @@ bool OpenProjectCommand::Apply(CommandExecutionContext context)
    }
    else
    {
-      context.GetProject()->OpenFile(fileName,addToHistory);
+      context.GetProject()->OpenFile(fileName, addToHistory);
    }
-   wxString newFileName = context.GetProject()->GetFileName();
+   const wxString &newFileName = context.GetProject()->GetFileName();
 
    // Because Open does not return a success or failure, we have to guess
    // at this point, based on whether the project file name has

src/ondemand/ODDecodeTask.cpp

@@ -290,8 +290,8 @@ int ODDecodeTask::GetNumFileDecoders()
 
 ///This should handle unicode converted to UTF-8 on mac/linux, but OD TODO:check on windows
 ODFileDecoder::ODFileDecoder(const wxString & fName)
+   : mFName{ fName }
 {
-   mFName = fName;
    mInited = false;
 }
 

src/ondemand/ODDecodeTask.h

@@ -120,7 +120,7 @@ public:
    ///returns negative value for failure, 0 or positive value for success.
    virtual int Decode(SampleBuffer & data, sampleFormat & format, sampleCount start, sampleCount len, unsigned int channel)=0;
 
-   wxString GetFileName(){return mFName;}
+   const wxString &GetFileName(){return mFName;}
 
    bool IsInitialized();
 
@@ -131,7 +131,7 @@ protected:
    bool     mInited;
    ODLock   mInitedLock;
 
-   wxString  mFName;
+   const wxString  mFName;
 
    unsigned int mSampleRate;
    unsigned int mNumSamples;//this may depend on the channel - so TODO: we should probably let the decoder create/modify the track info directly.