Created attachment 187214 [details]
Repro in O'Caml

Copying text containing CRLF line endings to the clipboard is broken in the current Windows port. For example, copying "Hello\r\nBye" using gtk_clipboard_set_text results in the text "Hello\r\r\nBye" on the clipboard.
The general phenomenon is that GTK/GDK replaces LFs by CRLFs, and it copies existing CRs as-is.

Repro
=====
- Run the O'Caml program clipboard_test.ml in attach.
- Run the C# program get_clipboard.cs in attach. The output is incorrect.

As evidence that the problem is in GTK/GDK and not in Windows or C#:
- Run the C# program set_clipboard.cs in attach.
- Run the C# program get_clipboard.cs in attach. The output is correct.

Proposed Fix
============

I believe the problem could be solved easily if the LF-to-CRLF conversion code in function _gdk_win32_window_change_property in file gdk/win32/gdkproperty-win32.c were made more robust so that it would properly convert LF, CR, and CRLF line endings to CRLF.

Detailed Control Flow
=====================

gtk_clipboard_set_text
  gtk_clipboard_set_with_data(get_func=text_get_func)
    gtk_target_list_add_text_targets
      adds targets utf8_atom (="UTF8_STRING") and others
    gtk_clipboard_set_contents
      gtk_selection_owner_set_for_display
        gdk_selection_owner_set_for_display
          _gdk_win32_display_set_selection_owner
            gdk_event_put(type=GDK_SELECTION_REQUEST, target=_utf8_string (="UTF8_STRING", see gdk/win32/gdkmain-win32.c))
      gtk_selection_add_targets
        gdk_win32_selection_add_targets // Only relevant for delay-rendered formats

gtk_main
  g_main_loop_run
    ...
      gtk_main_do_event(event.type=GDK_SELECTION_REQUEST)
        gtk_widget_event
          gtk_widget_event_internal
            g_signal_emit(signal="selection-request-event")
              _gtk_selection_request
                gtk_selection_invoke_handler
                  g_signal_emit_by_name("selection-get", data, info)
                    "selection-get" event on clipboard widget
                       selection_get_cb (in gtk/gtkselection.c)
                         text_get_func
                           gtk_selection_data_set_text
                             gtk_selection_data_set
                gdk_property_change
                  _gdk_win32_window_change_property (in gdk/win32/gdkproperty-win32.c)
                     SetClipboardData(CF_UNICODETEXT, lf2crlf(data))

There are a number of places in gdk/win32/gdkselection-win32.c and gtk/gtkselection.c where the required conversions are done but these are not on the code path that results from a gtk_selection_set_text call.