Don't allow using GetPath/GetFilename() with wxFD_MULTIPLE

GetPaths/GetFilenames() must be used instead when more than one file
could be selected: document this and assert if the wrong functions are
called.

Closes https://github.com/wxWidgets/wxWidgets/pull/1883

docs/changes.txt

@@ -99,6 +99,9 @@ Changes in behaviour not resulting in compilation errors
 - wxSizer::RecalcSizes() shouldn't be called directly (note that it was never
   supposed to be called, only implemented), call Layout() instead.
 
+- wxFileDialog::GetPath() and wxFileDialog::GetFilename() now assert and return
+  an empty string if called on dialogs with the wxFD_MULTIPLE style.
+
 
 Changes in behaviour which may result in build errors
 -----------------------------------------------------

include/wx/filedlg.h

@@ -104,10 +104,19 @@ public:
     virtual void SetFilterIndex(int filterIndex) { m_filterIndex = filterIndex; }
 
     virtual wxString GetMessage() const { return m_message; }
-    virtual wxString GetPath() const { return m_path; }
+    virtual wxString GetPath() const
+    {
+        wxCHECK_MSG( !HasFlag(wxFD_MULTIPLE), wxString(), "When using wxFD_MULTIPLE, must call GetPaths() instead" );
+        return m_path;
+    }
+
     virtual void GetPaths(wxArrayString& paths) const { paths.Empty(); paths.Add(m_path); }
     virtual wxString GetDirectory() const { return m_dir; }
-    virtual wxString GetFilename() const { return m_fileName; }
+    virtual wxString GetFilename() const
+    {
+        wxCHECK_MSG( !HasFlag(wxFD_MULTIPLE), wxString(), "When using wxFD_MULTIPLE, must call GetFilenames() instead" );
+        return m_fileName;
+    }
     virtual void GetFilenames(wxArrayString& files) const { files.Empty(); files.Add(m_fileName); }
     virtual wxString GetWildcard() const { return m_wildCard; }
     virtual int GetFilterIndex() const { return m_filterIndex; }

include/wx/generic/filedlgg.h

@@ -73,13 +73,19 @@ public:
         { m_filectrl->SetWildcard(wildCard); }
 
     virtual wxString GetPath() const wxOVERRIDE
-        { return m_filectrl->GetPath(); }
+        {
+            wxCHECK_MSG( !HasFlag(wxFD_MULTIPLE), wxString(), "When using wxFD_MULTIPLE, must call GetPaths() instead" );
+            return m_filectrl->GetPath();
+        }
     virtual void GetPaths(wxArrayString& paths) const wxOVERRIDE
         { m_filectrl->GetPaths(paths); }
     virtual wxString GetDirectory() const wxOVERRIDE
         { return m_filectrl->GetDirectory(); }
     virtual wxString GetFilename() const wxOVERRIDE
-        { return m_filectrl->GetFilename(); }
+        {
+            wxCHECK_MSG( !HasFlag(wxFD_MULTIPLE), wxString(), "When using wxFD_MULTIPLE, must call GetFilenames() instead" );
+            return m_filectrl->GetFilename();
+        }
     virtual void GetFilenames(wxArrayString& files) const wxOVERRIDE
         { m_filectrl->GetFilenames(files); }
     virtual wxString GetWildcard() const wxOVERRIDE

interface/wx/filedlg.h

@@ -264,6 +264,9 @@ public:
 
     /**
         Returns the default filename.
+
+        @note This function can't be used with dialogs which have the @c wxFD_MULTIPLE style,
+              use GetFilenames() instead.
     */
     virtual wxString GetFilename() const;
 
@@ -298,6 +301,9 @@ public:
 
     /**
         Returns the full path (directory and filename) of the selected file.
+
+        @note This function can't be used with dialogs which have the @c wxFD_MULTIPLE style,
+              use GetPaths() instead.
     */
     virtual wxString GetPath() const;
 

src/gtk/filedlg.cpp

@@ -396,6 +396,7 @@ void wxFileDialog::OnSize(wxSizeEvent&)
 
 wxString wxFileDialog::GetPath() const
 {
+    wxCHECK_MSG( !HasFlag(wxFD_MULTIPLE), wxString(), "When using wxFD_MULTIPLE, must call GetPaths() instead" );
     return m_fc.GetPath();
 }
 
@@ -463,6 +464,8 @@ void wxFileDialog::SetFilename(const wxString& name)
 
 wxString wxFileDialog::GetFilename() const
 {
+    wxCHECK_MSG( !HasFlag(wxFD_MULTIPLE), wxString(), "When using wxFD_MULTIPLE, must call GetFilenames() instead" );
+
     wxString currentFilename( m_fc.GetFilename() );
     if (currentFilename.empty())
     {

src/qt/filedlg.cpp

@@ -103,6 +103,8 @@ bool wxFileDialog::Create(wxWindow *parent,
 
 wxString wxFileDialog::GetPath() const
 {
+    wxCHECK_MSG( !HasFlag(wxFD_MULTIPLE), wxString(), "When using wxFD_MULTIPLE, must call GetPaths() instead" );
+
     wxArrayString paths;
     GetPaths(paths);
     if (paths.empty())
@@ -120,6 +122,8 @@ void wxFileDialog::GetPaths(wxArrayString& paths) const
 
 wxString wxFileDialog::GetFilename() const
 {
+    wxCHECK_MSG( !HasFlag(wxFD_MULTIPLE), wxString(), "When using wxFD_MULTIPLE, must call GetFilenames() instead" );
+
     wxArrayString filenames;
     GetFilenames(filenames);
     if ( filenames.empty() )