Remove old mentions and uses of ipython_extension_dir (#14310)

The bulk of this functionality was removed in IPython 8.6.0, but there
were still mentions of it in the docs and in the reload code.

The extant mentions of `.ipython/extensions` in code came up as a source
of confusion in  #14263.

IPython/core/extensions.py

@@ -1,150 +1,135 b''
 # encoding: utf-8
 """A class for managing IPython extensions."""
 
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
 import os
 import os.path
 import sys
 from importlib import import_module, reload
 
 from traitlets.config.configurable import Configurable
 from IPython.utils.path import ensure_dir_exists
 from traitlets import Instance
 
 
 #-----------------------------------------------------------------------------
 # Main class
 #-----------------------------------------------------------------------------
 
 BUILTINS_EXTS = {"storemagic": False, "autoreload": False}
 
 
 class ExtensionManager(Configurable):
     """A class to manage IPython extensions.
 
     An IPython extension is an importable Python module that has
     a function with the signature::
 
         def load_ipython_extension(ipython):
             # Do things with ipython
 
     This function is called after your extension is imported and the
     currently active :class:`InteractiveShell` instance is passed as
     the only argument.  You can do anything you want with IPython at
     that point, including defining new magic and aliases, adding new
     components, etc.
     
     You can also optionally define an :func:`unload_ipython_extension(ipython)`
     function, which will be called if the user unloads or reloads the extension.
     The extension manager will only call :func:`load_ipython_extension` again
     if the extension is reloaded.
 
     You can put your extension modules anywhere you want, as long as
-    they can be imported by Python's standard import mechanism.  However,
-    to make it easy to write extensions, you can also put your extensions
-    in ``os.path.join(self.ipython_dir, 'extensions')``.  This directory
-    is added to ``sys.path`` automatically.
+    they can be imported by Python's standard import mechanism.
     """
 
     shell = Instance('IPython.core.interactiveshell.InteractiveShellABC', allow_none=True)
 
     def __init__(self, shell=None, **kwargs):
         super(ExtensionManager, self).__init__(shell=shell, **kwargs)
-        self.shell.observe(
-            self._on_ipython_dir_changed, names=('ipython_dir',)
-        )
         self.loaded = set()
 
-    @property
-    def ipython_extension_dir(self):
-        return os.path.join(self.shell.ipython_dir, u'extensions')
-
-    def _on_ipython_dir_changed(self, change):
-        ensure_dir_exists(self.ipython_extension_dir)
-
     def load_extension(self, module_str: str):
         """Load an IPython extension by its module name.
 
         Returns the string "already loaded" if the extension is already loaded,
         "no load function" if the module doesn't have a load_ipython_extension
         function, or None if it succeeded.
         """
         try:
             return self._load_extension(module_str)
         except ModuleNotFoundError:
             if module_str in BUILTINS_EXTS:
                 BUILTINS_EXTS[module_str] = True
                 return self._load_extension("IPython.extensions." + module_str)
             raise
 
     def _load_extension(self, module_str: str):
         if module_str in self.loaded:
             return "already loaded"
 
         assert self.shell is not None
 
         with self.shell.builtin_trap:
             if module_str not in sys.modules:
                 mod = import_module(module_str)
             mod = sys.modules[module_str]
             if self._call_load_ipython_extension(mod):
                 self.loaded.add(module_str)
             else:
                 return "no load function"
 
     def unload_extension(self, module_str: str):
         """Unload an IPython extension by its module name.
 
         This function looks up the extension's name in ``sys.modules`` and
         simply calls ``mod.unload_ipython_extension(self)``.
 
         Returns the string "no unload function" if the extension doesn't define
         a function to unload itself, "not loaded" if the extension isn't loaded,
         otherwise None.
         """
         if BUILTINS_EXTS.get(module_str, False) is True:
             module_str = "IPython.extensions." + module_str
         if module_str not in self.loaded:
             return "not loaded"
 
         if module_str in sys.modules:
             mod = sys.modules[module_str]
             if self._call_unload_ipython_extension(mod):
                 self.loaded.discard(module_str)
             else:
                 return "no unload function"
 
     def reload_extension(self, module_str: str):
         """Reload an IPython extension by calling reload.
 
         If the module has not been loaded before,
         :meth:`InteractiveShell.load_extension` is called. Otherwise
         :func:`reload` is called and then the :func:`load_ipython_extension`
         function of the module, if it exists is called.
         """
-        from IPython.utils.syspathcontext import prepended_to_syspath
 
         if BUILTINS_EXTS.get(module_str, False) is True:
             module_str = "IPython.extensions." + module_str
 
         if (module_str in self.loaded) and (module_str in sys.modules):
             self.unload_extension(module_str)
             mod = sys.modules[module_str]
-            with prepended_to_syspath(self.ipython_extension_dir):
                 reload(mod)
             if self._call_load_ipython_extension(mod):
                 self.loaded.add(module_str)
         else:
             self.load_extension(module_str)
 
     def _call_load_ipython_extension(self, mod):
         if hasattr(mod, 'load_ipython_extension'):
             mod.load_ipython_extension(self.shell)
             return True
 
     def _call_unload_ipython_extension(self, mod):
         if hasattr(mod, 'unload_ipython_extension'):
             mod.unload_ipython_extension(self.shell)
             return True