Prefer execution when there's only a single line entered

Closes gh-10425

The heuristic here is to treat a single line specially, and always
evaluate it as if the cursor was at the end. An alternative heuristic
could be to do this if the cursor is on the last line of the input.

IPython/terminal/shortcuts.py

@@ -1,246 +1,251 b''
 """
 Module to define and register Terminal IPython shortcuts with
 :mod:`prompt_toolkit`
 """
 
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
 import warnings
 import signal
 import sys
 from typing import Callable
 
 
 from prompt_toolkit.enums import DEFAULT_BUFFER, SEARCH_BUFFER
 from prompt_toolkit.filters import (HasFocus, HasSelection, Condition,
     ViInsertMode, EmacsInsertMode, HasCompletions)
 from prompt_toolkit.filters.cli import ViMode, ViNavigationMode
 from prompt_toolkit.keys import Keys
 from prompt_toolkit.key_binding.bindings.completion import display_completions_like_readline
 
 from IPython.utils.decorators import undoc
 
 @undoc
 @Condition
 def cursor_in_leading_ws(cli):
     before = cli.application.buffer.document.current_line_before_cursor
     return (not before) or before.isspace()
 
 def register_ipython_shortcuts(registry, shell):
     """Set up the prompt_toolkit keyboard shortcuts for IPython"""
     insert_mode = ViInsertMode() | EmacsInsertMode()
 
     # Ctrl+J == Enter, seemingly
     registry.add_binding(Keys.ControlJ,
                          filter=(HasFocus(DEFAULT_BUFFER)
                                  & ~HasSelection()
                                  & insert_mode
                         ))(newline_or_execute_outer(shell))
 
     registry.add_binding(Keys.ControlBackslash)(force_exit)
 
     registry.add_binding(Keys.ControlP,
                          filter=(ViInsertMode() & HasFocus(DEFAULT_BUFFER)
                         ))(previous_history_or_previous_completion)
 
     registry.add_binding(Keys.ControlN,
                          filter=(ViInsertMode() & HasFocus(DEFAULT_BUFFER)
                         ))(next_history_or_next_completion)
 
     registry.add_binding(Keys.ControlG,
                          filter=(HasFocus(DEFAULT_BUFFER) & HasCompletions()
                         ))(dismiss_completion)
 
     registry.add_binding(Keys.ControlC, filter=HasFocus(DEFAULT_BUFFER)
                         )(reset_buffer)
 
     registry.add_binding(Keys.ControlC, filter=HasFocus(SEARCH_BUFFER)
                         )(reset_search_buffer)
 
     supports_suspend = Condition(lambda cli: hasattr(signal, 'SIGTSTP'))
     registry.add_binding(Keys.ControlZ, filter=supports_suspend
                         )(suspend_to_bg)
 
     # Ctrl+I == Tab
     registry.add_binding(Keys.ControlI,
                          filter=(HasFocus(DEFAULT_BUFFER)
                                  & ~HasSelection()
                                  & insert_mode
                                  & cursor_in_leading_ws
                         ))(indent_buffer)
 
     registry.add_binding(Keys.ControlO,
                          filter=(HasFocus(DEFAULT_BUFFER)
                                 & EmacsInsertMode()))(newline_autoindent_outer(shell.input_splitter))
 
     registry.add_binding(Keys.F2,
                          filter=HasFocus(DEFAULT_BUFFER)
                         )(open_input_in_editor)
 
     if shell.display_completions == 'readlinelike':
         registry.add_binding(Keys.ControlI,
                              filter=(HasFocus(DEFAULT_BUFFER)
                                      & ~HasSelection()
                                      & insert_mode
                                      & ~cursor_in_leading_ws
                             ))(display_completions_like_readline)
 
     if sys.platform == 'win32':
         registry.add_binding(Keys.ControlV,
                              filter=(
                              HasFocus(
                              DEFAULT_BUFFER) & ~ViMode()
                             ))(win_paste)
 
 
 def newline_or_execute_outer(shell):
     def newline_or_execute(event):
         """When the user presses return, insert a newline or execute the code."""
         b = event.current_buffer
         d = b.document
 
         if b.complete_state:
             cc = b.complete_state.current_completion
             if cc:
                 b.apply_completion(cc)
             else:
                 b.cancel_completion()
             return
 
-        before_text = d.text[:d.cursor_position]
-        status, indent = shell.input_splitter.check_complete(before_text + '\n')
+        # If there's only one line, treat it as if the cursor is at the end.
+        # See https://github.com/ipython/ipython/issues/10425
+        if d.line_count == 1:
+            check_text = d.text
+        else:
+            check_text = d.text[:d.cursor_position]
+        status, indent = shell.input_splitter.check_complete(check_text + '\n')
 
         if not (d.on_last_line or
                 d.cursor_position_row >= d.line_count - d.empty_line_count_at_the_end()
                 ):
             b.insert_text('\n' + (' ' * (indent or 0)))
             return
 
         if (status != 'incomplete') and b.accept_action.is_returnable:
             b.accept_action.validate_and_handle(event.cli, b)
         else:
             b.insert_text('\n' + (' ' * (indent or 0)))
     return newline_or_execute
 
 
 def previous_history_or_previous_completion(event):
     """
     Control-P in vi edit mode on readline is history next, unlike default prompt toolkit.
 
     If completer is open this still select previous completion.
     """
     event.current_buffer.auto_up()
 
 
 def next_history_or_next_completion(event):
     """
     Control-N in vi edit mode on readline is history previous, unlike default prompt toolkit.
 
     If completer is open this still select next completion.
     """
     event.current_buffer.auto_down()
 
 
 def dismiss_completion(event):
     b = event.current_buffer
     if b.complete_state:
         b.cancel_completion()
 
 
 def reset_buffer(event):
     b = event.current_buffer
     if b.complete_state:
         b.cancel_completion()
     else:
         b.reset()
 
 
 def reset_search_buffer(event):
     if event.current_buffer.document.text:
         event.current_buffer.reset()
     else:
         event.cli.push_focus(DEFAULT_BUFFER)
 
 def suspend_to_bg(event):
     event.cli.suspend_to_background()
 
 def force_exit(event):
     """
     Force exit (with a non-zero return value)
     """
     sys.exit("Quit")
 
 def indent_buffer(event):
     event.current_buffer.insert_text(' ' * 4)
 
 @undoc
 def newline_with_copy_margin(event):
     """
     DEPRECATED since IPython 6.0
 
     See :any:`newline_autoindent_outer` for a replacement.
 
     Preserve margin and cursor position when using
     Control-O to insert a newline in EMACS mode
     """
     warnings.warn("`newline_with_copy_margin(event)` is deprecated since IPython 6.0. "
       "see `newline_autoindent_outer(shell)(event)` for a replacement.",
                   DeprecationWarning, stacklevel=2)
 
     b = event.current_buffer
     cursor_start_pos = b.document.cursor_position_col
     b.newline(copy_margin=True)
     b.cursor_up(count=1)
     cursor_end_pos = b.document.cursor_position_col
     if cursor_start_pos != cursor_end_pos:
         pos_diff = cursor_start_pos - cursor_end_pos
         b.cursor_right(count=pos_diff)
 
 def newline_autoindent_outer(inputsplitter) -> Callable[..., None]:
     """
     Return a function suitable for inserting a indented newline after the cursor.
 
     Fancier version of deprecated ``newline_with_copy_margin`` which should
     compute the correct indentation of the inserted line. That is to say, indent
     by 4 extra space after a function definition, class definition, context
     manager... And dedent by 4 space after ``pass``, ``return``, ``raise ...``.
     """
 
     def newline_autoindent(event):
         """insert a newline after the cursor indented appropriately."""
         b = event.current_buffer
         d = b.document
 
         if b.complete_state:
             b.cancel_completion()
         text = d.text[:d.cursor_position] + '\n'
         _, indent = inputsplitter.check_complete(text)
         b.insert_text('\n' + (' ' * (indent or 0)), move_cursor=False)
 
     return newline_autoindent
 
 
 def open_input_in_editor(event):
     event.cli.current_buffer.tempfile_suffix = ".py"
     event.cli.current_buffer.open_in_editor(event.cli)
 
 
 if sys.platform == 'win32':
     from IPython.core.error import TryNext
     from IPython.lib.clipboard import (ClipboardEmpty,
                                        win32_clipboard_get,
                                        tkinter_clipboard_get)
 
     @undoc
     def win_paste(event):
         try:
             text = win32_clipboard_get()
         except TryNext:
             try:
                 text = tkinter_clipboard_get()
             except (TryNext, ClipboardEmpty):
                 return
         except ClipboardEmpty:
             return
         event.current_buffer.insert_text(text.replace('\t', ' ' * 4))