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)
+            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