Bug2135: startup should not fail quietly when audacity.cfg is locked...

simplest fix is simply to put up a message box explaining it

src/AudacityApp.cpp

@@ -1360,6 +1360,13 @@ bool AudacityApp::OnInit()
    // Initialize preferences and language
    InitPreferences();
    PopulatePreferences();
+   // This test must follow PopulatePreferences, because if an error message
+   // must be shown, we need internationalization to have been initialized
+   // first, which was done in PopulatePreferences
+   if ( !CheckWritablePreferences() ) {
+      ::AudacityMessageBox( UnwritablePreferencesErrorMessage() );
+      return false;
+   }
 
 #if defined(__WXMSW__) && !defined(__WXUNIVERSAL__) && !defined(__CYGWIN__)
    this->AssociateFileTypes();

src/Prefs.cpp

@@ -61,6 +61,7 @@
 #include <wx/stdpaths.h>
 
 #include "FileNames.h"
+#include "Internat.h"
 #include "MemoryX.h"
 #include "Languages.h"
 
@@ -220,6 +221,20 @@ void InitPreferences()
    wxConfigBase::Set(gPrefs);
 }
 
+bool CheckWritablePreferences()
+{
+   return gPrefs->Write("/TEST", true) && gPrefs->Flush();
+}
+
+wxString UnwritablePreferencesErrorMessage()
+{
+   wxFileName configFileName(FileNames::DataDir(), wxT("audacity.cfg"));
+   return wxString::Format(
+     _("Audacity cannot start because the settings file at %s is not writable."),
+     configFileName.GetFullPath()
+   );
+}
+
 void FinishPreferences()
 {
    if (gPrefs) {

src/Prefs.h

@@ -38,6 +38,8 @@
 #include <wx/event.h> // to declare custom event types
 
 void InitPreferences();
+bool CheckWritablePreferences();
+wxString UnwritablePreferencesErrorMessage();
 void FinishPreferences();
 
 class AudacityPrefs;