Remove input_prefilter hook

Our code already doesn't call this hook (as pointed out in gh-4709), and
probably hasn't for some time, so it seems ~no-one is relying on it. We
have much more powerful APIs to do the same thing.

docs/source/whatsnew/pr/incompat-input-prefilter-hook.rst

@@ -0,0 +1,4 b''
+* The ``input_prefilter`` hook has been removed, as it was never
+  actually used by the code. The input transformer system offers much
+  more powerful APIs to work with input code. See
+  :doc:`/config/inputtransforms` for details.

IPython/core/hooks.py

@@ -1,224 +1,209 b''
 """Hooks for IPython.
 
 In Python, it is possible to overwrite any method of any object if you really
 want to.  But IPython exposes a few 'hooks', methods which are *designed* to
 be overwritten by users for customization purposes.  This module defines the
 default versions of all such hooks, which get used by IPython if not
 overridden by the user.
 
 Hooks are simple functions, but they should be declared with ``self`` as their
 first argument, because when activated they are registered into IPython as
 instance methods. The self argument will be the IPython running instance
 itself, so hooks have full access to the entire IPython object.
 
 If you wish to define a new hook and activate it, you can make an :doc:`extension
 </config/extensions/index>` or a :ref:`startup script <startup_files>`. For
 example, you could use a startup file like this::
 
     import os
 
     def calljed(self,filename, linenum):
         "My editor hook calls the jed editor directly."
         print "Calling my own editor, jed ..."
         if os.system('jed +%d %s' % (linenum,filename)) != 0:
             raise TryNext()
 
     def load_ipython_extension(ip):
         ip.set_hook('editor', calljed)
 
 """
 
 #*****************************************************************************
 #       Copyright (C) 2005 Fernando Perez. <[e-mail]>
 #
 #  Distributed under the terms of the BSD License.  The full license is in
 #  the file COPYING, distributed as part of this software.
 #*****************************************************************************
 
 import os
 import subprocess
 import sys
 
 from IPython.core.error import TryNext
 
 # List here all the default hooks.  For now it's just the editor functions
 # but over time we'll move here all the public API for user-accessible things.
 
 __all__ = ['editor', 'fix_error_editor', 'synchronize_with_editor',
-           'input_prefilter', 'shutdown_hook', 'late_startup_hook',
+           'shutdown_hook', 'late_startup_hook',
            'show_in_pager','pre_prompt_hook',
            'pre_run_code_hook', 'clipboard_get']
 
 def editor(self, filename, linenum=None, wait=True):
     """Open the default editor at the given filename and linenumber.
 
     This is IPython's default editor hook, you can use it as an example to
     write your own modified one.  To set your own editor function as the
     new editor hook, call ip.set_hook('editor',yourfunc)."""
 
     # IPython configures a default editor at startup by reading $EDITOR from
     # the environment, and falling back on vi (unix) or notepad (win32).
     editor = self.editor
 
     # marker for at which line to open the file (for existing objects)
     if linenum is None or editor=='notepad':
         linemark = ''
     else:
         linemark = '+%d' % int(linenum)
 
     # Enclose in quotes if necessary and legal
     if ' ' in editor and os.path.isfile(editor) and editor[0] != '"':
         editor = '"%s"' % editor
 
     # Call the actual editor
     proc = subprocess.Popen('%s %s %s' % (editor, linemark, filename),
                             shell=True)
     if wait and proc.wait() != 0:
         raise TryNext()
 
 import tempfile
 def fix_error_editor(self,filename,linenum,column,msg):
     """Open the editor at the given filename, linenumber, column and
     show an error message. This is used for correcting syntax errors.
     The current implementation only has special support for the VIM editor,
     and falls back on the 'editor' hook if VIM is not used.
 
     Call ip.set_hook('fix_error_editor',youfunc) to use your own function,
     """
     def vim_quickfix_file():
         t = tempfile.NamedTemporaryFile()
         t.write('%s:%d:%d:%s\n' % (filename,linenum,column,msg))
         t.flush()
         return t
     if os.path.basename(self.editor) != 'vim':
         self.hooks.editor(filename,linenum)
         return
     t = vim_quickfix_file()
     try:
         if os.system('vim --cmd "set errorformat=%f:%l:%c:%m" -q ' + t.name):
             raise TryNext()
     finally:
         t.close()
 
 
 def synchronize_with_editor(self, filename, linenum, column):
         pass
 
 
 class CommandChainDispatcher:
     """ Dispatch calls to a chain of commands until some func can handle it
 
     Usage: instantiate, execute "add" to add commands (with optional
     priority), execute normally via f() calling mechanism.
 
     """
     def __init__(self,commands=None):
         if commands is None:
             self.chain = []
         else:
             self.chain = commands
 
 
     def __call__(self,*args, **kw):
         """ Command chain is called just like normal func.
 
         This will call all funcs in chain with the same args as were given to
         this function, and return the result of first func that didn't raise
         TryNext"""
         last_exc = TryNext()
         for prio,cmd in self.chain:
             #print "prio",prio,"cmd",cmd #dbg
             try:
                 return cmd(*args, **kw)
             except TryNext as exc:
                 last_exc = exc
         # if no function will accept it, raise TryNext up to the caller
         raise last_exc
 
     def __str__(self):
         return str(self.chain)
 
     def add(self, func, priority=0):
         """ Add a func to the cmd chain with given priority """
         self.chain.append((priority, func))
         self.chain.sort(key=lambda x: x[0])
 
     def __iter__(self):
         """ Return all objects in chain.
 
         Handy if the objects are not callable.
         """
         return iter(self.chain)
 
 
-def input_prefilter(self,line):
-    """ Default input prefilter
-
-    This returns the line as unchanged, so that the interpreter
-    knows that nothing was done and proceeds with "classic" prefiltering
-    (%magics, !shell commands etc.).
-
-    Note that leading whitespace is not passed to this hook. Prefilter
-    can't alter indentation.
-
-    """
-    #print "attempt to rewrite",line #dbg
-    return line
-
-
 def shutdown_hook(self):
     """ default shutdown hook
 
     Typically, shotdown hooks should raise TryNext so all shutdown ops are done
     """
 
     #print "default shutdown hook ok" # dbg
     return
 
 
 def late_startup_hook(self):
     """ Executed after ipython has been constructed and configured
 
     """
     #print "default startup hook ok" # dbg
 
 
 def show_in_pager(self,s):
     """ Run a string through pager """
     # raising TryNext here will use the default paging functionality
     raise TryNext
 
 
 def pre_prompt_hook(self):
     """ Run before displaying the next prompt
 
     Use this e.g. to display output from asynchronous operations (in order
     to not mess up text entry)
     """
 
     return None
 
 
 def pre_run_code_hook(self):
     """ Executed before running the (prefiltered) code in IPython """
     return None
 
 
 def clipboard_get(self):
     """ Get text from the clipboard.
     """
     from IPython.lib.clipboard import (
         osx_clipboard_get, tkinter_clipboard_get,
         win32_clipboard_get
     )
     if sys.platform == 'win32':
         chain = [win32_clipboard_get, tkinter_clipboard_get]
     elif sys.platform == 'darwin':
         chain = [osx_clipboard_get, tkinter_clipboard_get]
     else:
         chain = [tkinter_clipboard_get]
     dispatcher = CommandChainDispatcher()
     for func in chain:
         dispatcher.add(func)
     text = dispatcher()
     return text