Improve support for TABs in wxListBox under MSW

Always set the LB_USETABSTOPS style flag to achieve behaviour more
compatible with other platforms and expand TABs to align them at tab
stops positioned at every 8 characters.

Also add MSW-specific MSWSetTabStops() method allowing to customize tab
stops.

Update the documentation and the sample to demonstrate using TABs.

Closes https://github.com/wxWidgets/wxWidgets/pull/1789

include/wx/msw/listbox.h

@@ -128,6 +128,10 @@ public:
     // extent of all strings is used. In any case calls InvalidateBestSize()
     virtual void SetHorizontalExtent(const wxString& s = wxEmptyString);
 
+    // This is a wrapper for LB_SETTABSTOPS message and takes tab stops in
+    // dialog units, with the same conventions as LB_SETTABSTOPS uses.
+    virtual bool MSWSetTabStops(const wxVector<int>& tabStops);
+
     // Windows callbacks
     bool MSWCommand(WXUINT param, WXWORD id) wxOVERRIDE;
     WXDWORD MSWGetStyle(long style, WXDWORD *exstyle) const wxOVERRIDE;

interface/wx/listbox.h

@@ -24,10 +24,7 @@
     performance nor from user interface point of view, for large number of
     items.
 
-    Notice that currently @c TAB characters in list box items text are not
+    Notice that the list box doesn't support control characters other than @c TAB.
-    handled consistently under all platforms, so they should be replaced by
-    spaces to display strings properly everywhere. The list box doesn't
-    support any other control characters at all.
 
     @beginStyleTable
     @style{wxLB_SINGLE}
@@ -321,6 +318,28 @@ public:
     */
     int GetTopItem() const;
 
+    /**
+        MSW-specific function for setting custom tab stop distances.
+
+        Tab stops are expressed in dialog unit widths, i.e. "quarters of the
+        average character width for the font that is selected into the list
+        box".
+
+        @param tabStops
+            If this argument is empty, tab stops are reset to their default
+            value (every 32 dialog units). If it contains a single element, tab
+            stops are set at each multiple of the given value. Otherwise tab
+            stops are set at every element of the array, which must be in
+            ascending order.
+
+        @return @true if all specified tabs are set, @false otherwise
+
+        @onlyfor{wxmsw}
+
+        @since 3.1.4
+     */
+    virtual void MSWSetTabStops(const wxVector<int>& tabStops);
+
     // NOTE: Phoenix needs to see the implementation of pure virtuals so it
     // knows that this class is not abstract.
     virtual unsigned int GetCount() const;
@@ -328,4 +347,3 @@ public:
     virtual void SetString(unsigned int n, const wxString& s);
     virtual int FindString(const wxString& s, bool bCase = false) const;
 };
-

samples/widgets/listbox.cpp

@@ -337,7 +337,7 @@ void ListboxWidgetsPage::CreateContent()
 
     wxSizer *sizerRow = new wxBoxSizer(wxHORIZONTAL);
     btn = new wxButton(this, ListboxPage_Add, "&Add this string");
-    m_textAdd = new wxTextCtrl(this, ListboxPage_AddText, "test item 0");
+    m_textAdd = new wxTextCtrl(this, ListboxPage_AddText, "test item \t0");
     sizerRow->Add(btn, 0, wxRIGHT, 5);
     sizerRow->Add(m_textAdd, 1, wxLEFT, 5);
     sizerMiddle->Add(sizerRow, 0, wxALL | wxGROW, 5);
@@ -619,7 +619,7 @@ void ListboxWidgetsPage::OnButtonAdd(wxCommandEvent& WXUNUSED(event))
     if ( !m_textAdd->IsModified() )
     {
         // update the default string
-        m_textAdd->SetValue(wxString::Format("test item %u", ++s_item));
+        m_textAdd->SetValue(wxString::Format("test item \t%u", ++s_item));
     }
 
     m_lbox->Append(s);

src/msw/listbox.cpp

@@ -187,6 +187,9 @@ WXDWORD wxListBox::MSWGetStyle(long style, WXDWORD *exstyle) const
     }
 #endif // wxUSE_OWNER_DRAWN
 
+    // tabs stops are expanded by default on linux/GTK and macOS/Cocoa
+    msStyle |= LBS_USETABSTOPS;
+
     return msStyle;
 }
 
@@ -611,6 +614,12 @@ void wxListBox::SetHorizontalExtent(const wxString& s)
     //else: it shouldn't change
 }
 
+bool wxListBox::MSWSetTabStops(const wxVector<int>& tabStops)
+{
+    return SendMessage(GetHwnd(), LB_SETTABSTOPS, (WPARAM)tabStops.size(),
+                       tabStops.size() ? (LPARAM)tabStops.begin() : NULL);
+}
+
 wxSize wxListBox::DoGetBestClientSize() const
 {
     // find the widest string