tweak history prefix search (up/^p) in qtconsole

moving the cursor around the line could result in
weird inconsistencies in the prefix.

This simplifies the logic by always using the cursor position
to set the history prefix,
and better determine when the history prefix has actually changed.

IPython/frontend/qt/console/history_console_widget.py

@@ -1,283 +1,295
 # System library imports
 from IPython.external.qt import QtGui
 
 # Local imports
 from IPython.utils.traitlets import Bool
 from console_widget import ConsoleWidget
 
 
 class HistoryConsoleWidget(ConsoleWidget):
     """ A ConsoleWidget that keeps a history of the commands that have been
         executed and provides a readline-esque interface to this history.
     """
 
     #------ Configuration ------------------------------------------------------
 
     # If enabled, the input buffer will become "locked" to history movement when
     # an edit is made to a multi-line input buffer. To override the lock, use
     # Shift in conjunction with the standard history cycling keys.
     history_lock = Bool(False, config=True)
 
     #---------------------------------------------------------------------------
     # 'object' interface
     #---------------------------------------------------------------------------
 
     def __init__(self, *args, **kw):
         super(HistoryConsoleWidget, self).__init__(*args, **kw)
 
         # HistoryConsoleWidget protected variables.
         self._history = []
         self._history_edits = {}
         self._history_index = 0
         self._history_prefix = ''
 
     #---------------------------------------------------------------------------
     # 'ConsoleWidget' public interface
     #---------------------------------------------------------------------------
 
     def execute(self, source=None, hidden=False, interactive=False):
         """ Reimplemented to the store history.
         """
         if not hidden:
             history = self.input_buffer if source is None else source
 
         executed = super(HistoryConsoleWidget, self).execute(
             source, hidden, interactive)
 
         if executed and not hidden:
             # Save the command unless it was an empty string or was identical
             # to the previous command.
             history = history.rstrip()
             if history and (not self._history or self._history[-1] != history):
                 self._history.append(history)
 
             # Emulate readline: reset all history edits.
             self._history_edits = {}
 
             # Move the history index to the most recent item.
             self._history_index = len(self._history)
 
         return executed
 
     #---------------------------------------------------------------------------
     # 'ConsoleWidget' abstract interface
     #---------------------------------------------------------------------------
 
     def _up_pressed(self, shift_modifier):
         """ Called when the up key is pressed. Returns whether to continue
             processing the event.
         """
         prompt_cursor = self._get_prompt_cursor()
         if self._get_cursor().blockNumber() == prompt_cursor.blockNumber():
             # Bail out if we're locked.
             if self._history_locked() and not shift_modifier:
                 return False
 
             # Set a search prefix based on the cursor position.
             col = self._get_input_buffer_cursor_column()
             input_buffer = self.input_buffer
-            if self._history_index == len(self._history) or \
-                    (self._history_prefix and col != len(self._history_prefix)):
+            # use the *shortest* of the cursor column and the history prefix
+            # to determine if the prefix has changed
+            n = min(col, len(self._history_prefix))
+            
+            # prefix changed, restart search from the beginning
+            if (self._history_prefix[:n] != input_buffer[:n]):
                 self._history_index = len(self._history)
+            
+            # the only time we shouldn't set the history prefix
+            # to the line up to the cursor is if we are already
+            # in a simple scroll (no prefix),
+            # and the cursor is at the end of the first line
+            first_line = input_buffer.split('\n', 1)[0]
+            if self._history_index == len(self._history) or \
+                not (self._history_prefix == '' and col == len(first_line)):
                 self._history_prefix = input_buffer[:col]
 
             # Perform the search.
             self.history_previous(self._history_prefix,
                                     as_prefix=not shift_modifier)
 
             # Go to the first line of the prompt for seemless history scrolling.
             # Emulate readline: keep the cursor position fixed for a prefix
             # search.
             cursor = self._get_prompt_cursor()
             if self._history_prefix:
                 cursor.movePosition(QtGui.QTextCursor.Right,
                                     n=len(self._history_prefix))
             else:
                 cursor.movePosition(QtGui.QTextCursor.EndOfLine)
             self._set_cursor(cursor)
 
             return False
 
         return True
 
     def _down_pressed(self, shift_modifier):
         """ Called when the down key is pressed. Returns whether to continue
             processing the event.
         """
         end_cursor = self._get_end_cursor()
         if self._get_cursor().blockNumber() == end_cursor.blockNumber():
             # Bail out if we're locked.
             if self._history_locked() and not shift_modifier:
                 return False
 
             # Perform the search.
             replaced = self.history_next(self._history_prefix,
                                             as_prefix=not shift_modifier)
 
             # Emulate readline: keep the cursor position fixed for a prefix
             # search. (We don't need to move the cursor to the end of the buffer
             # in the other case because this happens automatically when the
             # input buffer is set.)
             if self._history_prefix and replaced:
                 cursor = self._get_prompt_cursor()
                 cursor.movePosition(QtGui.QTextCursor.Right,
                                     n=len(self._history_prefix))
                 self._set_cursor(cursor)
 
             return False
 
         return True
 
     #---------------------------------------------------------------------------
     # 'HistoryConsoleWidget' public interface
     #---------------------------------------------------------------------------
 
     def history_previous(self, substring='', as_prefix=True):
         """ If possible, set the input buffer to a previous history item.
 
         Parameters:
         -----------
         substring : str, optional
             If specified, search for an item with this substring.
         as_prefix : bool, optional
             If True, the substring must match at the beginning (default).
 
         Returns:
         --------
         Whether the input buffer was changed.
         """
         index = self._history_index
         replace = False
         while index > 0:
             index -= 1
             history = self._get_edited_history(index)
             if (as_prefix and history.startswith(substring)) \
                 or (not as_prefix and substring in history):
                 replace = True
                 break
 
         if replace:
             self._store_edits()
             self._history_index = index
             self.input_buffer = history
 
         return replace
 
     def history_next(self, substring='', as_prefix=True):
         """ If possible, set the input buffer to a subsequent history item.
 
         Parameters:
         -----------
         substring : str, optional
             If specified, search for an item with this substring.
         as_prefix : bool, optional
             If True, the substring must match at the beginning (default).
 
         Returns:
         --------
         Whether the input buffer was changed.
         """
         index = self._history_index
         replace = False
         while self._history_index < len(self._history):
             index += 1
             history = self._get_edited_history(index)
             if (as_prefix and history.startswith(substring)) \
                 or (not as_prefix and substring in history):
                 replace = True
                 break
 
         if replace:
             self._store_edits()
             self._history_index = index
             self.input_buffer = history
 
         return replace
 
     def history_tail(self, n=10):
         """ Get the local history list.
 
         Parameters:
         -----------
         n : int
             The (maximum) number of history items to get.
         """
         return self._history[-n:]
 
     def _request_update_session_history_length(self):
         msg_id = self.kernel_manager.shell_channel.execute('',
             silent=True,
             user_expressions={
                 'hlen':'len(get_ipython().history_manager.input_hist_raw)',
                 }
             )
         self._request_info['execute'][msg_id] = self._ExecutionRequest(msg_id, 'save_magic')
 
     def _handle_execute_reply(self, msg):
         """ Handles replies for code execution, here only session history length
         """
         msg_id = msg['parent_header']['msg_id']
         info = self._request_info['execute'].pop(msg_id,None)
         if info and info.kind == 'save_magic' and not self._hidden:
             content = msg['content']
             status = content['status']
             if status == 'ok':
                 self._max_session_history=(int(content['user_expressions']['hlen']))
 
     def save_magic(self):
         # update the session history length
         self._request_update_session_history_length()
 
         file_name,extFilter = QtGui.QFileDialog.getSaveFileName(self,
             "Enter A filename",
             filter='Python File (*.py);; All files (*.*)'
             )
 
         # let's the user search/type for a file name, while the history length
         # is fetched
 
         if file_name:
             hist_range, ok = QtGui.QInputDialog.getText(self,
                 'Please enter an interval of command to save',
                 'Saving commands:',
                 text=str('1-'+str(self._max_session_history))
                 )
             if ok:
                 self.execute("%save"+" "+file_name+" "+str(hist_range))
 
     #---------------------------------------------------------------------------
     # 'HistoryConsoleWidget' protected interface
     #---------------------------------------------------------------------------
 
     def _history_locked(self):
         """ Returns whether history movement is locked.
         """
         return (self.history_lock and
                 (self._get_edited_history(self._history_index) !=
                  self.input_buffer) and
                 (self._get_prompt_cursor().blockNumber() !=
                  self._get_end_cursor().blockNumber()))
 
     def _get_edited_history(self, index):
         """ Retrieves a history item, possibly with temporary edits.
         """
         if index in self._history_edits:
             return self._history_edits[index]
         elif index == len(self._history):
             return unicode()
         return self._history[index]
 
     def _set_history(self, history):
         """ Replace the current history with a sequence of history items.
         """
         self._history = list(history)
         self._history_edits = {}
         self._history_index = len(self._history)
 
     def _store_edits(self):
         """ If there are edits to the current input buffer, store them.
         """
         current = self.input_buffer
         if self._history_index == len(self._history) or \
                 self._history[self._history_index] != current:
             self._history_edits[self._history_index] = current