ConsoleWidget now manually controls the vertical scrollbar.

As a result, Ctrl+L works as expected. Additionally, the prompt does not "jump around" while scrolling through history.

IPython/frontend/qt/console/console_widget.py

@@ -204,6 +204,12 b' class ConsoleWidget(Configurable, QtGui.QWidget):'
     # 'QWidget' interface
     #---------------------------------------------------------------------------
 
+    def resizeEvent(self, event):
+        """ Adjust the scrollbars manually after a resize event.
+        """
+        super(ConsoleWidget, self).resizeEvent(event)
+        self._adjust_scrollbars()
+
     def sizeHint(self):
         """ Reimplemented to suggest a size that is 80 characters wide and
             25 lines high.
@@ -462,6 +468,18 b' class ConsoleWidget(Configurable, QtGui.QWidget):'
         """
         self._control.print_(printer)
 
+    def prompt_to_top(self):
+        """ Moves the prompt to the top of the viewport.
+        """
+        if not self._executing:
+            scrollbar = self._control.verticalScrollBar()
+            scrollbar.setValue(scrollbar.maximum())
+            cursor = self._control.textCursor()
+            self._control.setTextCursor(self._get_prompt_cursor())
+            self._control.ensureCursorVisible()
+            QtGui.qApp.processEvents(QtCore.QEventLoop.ExcludeUserInputEvents)
+            self._control.setTextCursor(cursor)
+            
     def redo(self):
         """ Redo the last operation. If there is no operation to redo, nothing
             happens.
@@ -682,12 +700,6 b' class ConsoleWidget(Configurable, QtGui.QWidget):'
         
         return menu
 
-    def _context_menu_show(self, pos):
-        """ Shows a context menu at the given QPoint (in widget coordinates).
-        """
-        menu = self._context_menu_make(pos)
-        menu.exec_(self._control.mapToGlobal(pos))
-
     def _control_key_down(self, modifiers, include_command=True):
         """ Given a KeyboardModifiers flags object, return whether the Control
         key is down.
@@ -723,11 +735,20 b' class ConsoleWidget(Configurable, QtGui.QWidget):'
 
         # Connect signals.
         control.cursorPositionChanged.connect(self._cursor_position_changed)
-        control.customContextMenuRequested.connect(self._context_menu_show)
+        control.customContextMenuRequested.connect(
+            self._custom_context_menu_requested)
         control.copyAvailable.connect(self.copy_available)
         control.redoAvailable.connect(self.redo_available)
         control.undoAvailable.connect(self.undo_available)
 
+        # Hijack the document size change signal to prevent Qt from adjusting
+        # the viewport's scrollbar. We are relying on an implementation detail
+        # of Q(Plain)TextEdit here, which is potentially dangerous, but without
+        # this functionality we cannot create a nice terminal interface.
+        layout = control.document().documentLayout()
+        layout.documentSizeChanged.disconnect()
+        layout.documentSizeChanged.connect(self._adjust_scrollbars)
+
         # Configure the control.
         control.setContextMenuPolicy(QtCore.Qt.CustomContextMenu)
         control.setReadOnly(True)
@@ -830,14 +851,7 b' class ConsoleWidget(Configurable, QtGui.QWidget):'
                 intercepted = True
 
             elif key == QtCore.Qt.Key_L:
-                # It would be better to simply move the prompt block to the top
-                # of the control viewport. QPlainTextEdit has a private method
-                # to do this (setTopBlock), but it cannot be duplicated here
-                # because it requires access to the QTextControl that underlies
-                # both QPlainTextEdit and QTextEdit. In short, this can only be
-                # achieved by appending newlines after the prompt, which is a
-                # gigantic hack and likely to cause other problems.
-                self.clear()
+                self.prompt_to_top()
                 intercepted = True
 
             elif key == QtCore.Qt.Key_O:
@@ -1354,6 +1368,13 b' class ConsoleWidget(Configurable, QtGui.QWidget):'
             else:
                 self._append_plain_text(text)
 
+    def _prompt_finished(self):
+        """ Called immediately after a prompt is finished, i.e. when some input
+            will be processed and a new prompt displayed.
+        """
+        self._control.setReadOnly(True)
+        self._prompt_finished_hook()
+
     def _prompt_started(self):
         """ Called immediately after a new prompt is displayed.
         """
@@ -1371,13 +1392,6 b' class ConsoleWidget(Configurable, QtGui.QWidget):'
         self._executing = False
         self._prompt_started_hook()
 
-    def _prompt_finished(self):
-        """ Called immediately after a prompt is finished, i.e. when some input
-            will be processed and a new prompt displayed.
-        """
-        self._control.setReadOnly(True)
-        self._prompt_finished_hook()
-
     def _readline(self, prompt='', callback=None):
         """ Reads one line of input from the user. 
 
@@ -1488,6 +1502,23 b' class ConsoleWidget(Configurable, QtGui.QWidget):'
 
     #------ Signal handlers ----------------------------------------------------
 
+    def _adjust_scrollbars(self):
+        """ Expands the vertical scrollbar beyond the range set by Qt.
+        """
+        # This code is adapted from _q_adjustScrollbars in qplaintextedit.cpp
+        # and qtextedit.cpp.
+        document = self._control.document()
+        scrollbar = self._control.verticalScrollBar()
+        viewport_height = self._control.viewport().height()
+        if isinstance(self._control, QtGui.QPlainTextEdit):
+            high = max(0, document.lineCount() - 1)
+            step = viewport_height / self._control.fontMetrics().lineSpacing()
+        else:
+            high = document.size().height()
+            step = viewport_height
+        scrollbar.setRange(0, high)
+        scrollbar.setPageStep(step)
+
     def _cursor_position_changed(self):
         """ Clears the temporary buffer based on the cursor position.
         """
@@ -1505,3 +1536,9 b' class ConsoleWidget(Configurable, QtGui.QWidget):'
             else:
                 self._clear_temporary_buffer()
                 self._text_completing_pos = 0
+
+    def _custom_context_menu_requested(self, pos):
+        """ Shows a context menu at the given QPoint (in widget coordinates).
+        """
+        menu = self._context_menu_make(pos)
+        menu.exec_(self._control.mapToGlobal(pos))