Fix set_next_input with prompt_toolkit 1.0.10

Closes gh-10229

IPython/terminal/interactiveshell.py

@@ -12,6 +12,7 b' from IPython.utils.terminal import toggle_set_term_title, set_term_title'
 from IPython.utils.process import abbrev_cwd
 from traitlets import Bool, Unicode, Dict, Integer, observe, Instance, Type, default, Enum, Union
 
+from prompt_toolkit.document import Document
 from prompt_toolkit.enums import DEFAULT_BUFFER, EditingMode
 from prompt_toolkit.filters import (HasFocus, Condition, IsDone)
 from prompt_toolkit.history import InMemoryHistory
@@ -399,7 +400,13 b' class TerminalInteractiveShell(InteractiveShell):'
 
     def pre_prompt(self):
         if self.rl_next_input:
-            self.pt_cli.application.buffer.text = cast_unicode_py2(self.rl_next_input)
+            # We can't set the buffer here, because it will be reset just after
+            # this. Adding a callable to pre_run_callables does what we need
+            # after the buffer is reset.
+            s = cast_unicode_py2(self.rl_next_input)
+            def set_doc():
+                self.pt_cli.application.buffer.document = Document(s)
+            self.pt_cli.pre_run_callables.append(set_doc)
             self.rl_next_input = None
 
     def interact(self, display_banner=DISPLAY_BANNER_DEPRECATED):