Don't add ipython unconditionally to sys.path

Load ext will already do it with a context manager.

This should remove false positive when import modules, whithout breaking
functionalities.

Maybe closes  #13294 (making this part of 8.0 release make sens).

IPython/core/application.py

@@ -185,6 +185,15 b' class BaseIPythonApplication(Application):'
                 get_ipython_package_dir(), u'config', u'profile', change['new']
         )
 
+    add_ipython_dir_to_sys_path = Bool(False,
+        """Should the IPython profile directory be added to sys path ?
+
+        This option was non-existing before IPython 8.0, and ipython_dir was added to
+        sys path to allow import of extensions present there. This was historical
+        baggage from when pip did not exist. This now default to false,
+        but can bet to true for legacy reasons
+        """).tag(config=True)
+
     ipython_dir = Unicode(
         help="""
         The name of the IPython directory. This directory is used for logging
@@ -294,21 +303,22 b' class BaseIPythonApplication(Application):'
             str_old = os.path.abspath(old)
             if str_old in sys.path:
                 sys.path.remove(str_old)
-        str_path = os.path.abspath(new)
-        sys.path.append(str_path)
-        ensure_dir_exists(new)
-        readme = os.path.join(new, 'README')
-        readme_src = os.path.join(get_ipython_package_dir(), u'config', u'profile', 'README')
-        if not os.path.exists(readme) and os.path.exists(readme_src):
-            shutil.copy(readme_src, readme)
-        for d in ('extensions', 'nbextensions'):
-            path = os.path.join(new, d)
-            try:
-                ensure_dir_exists(path)
-            except OSError as e:
-                # this will not be EEXIST
-                self.log.error("couldn't create path %s: %s", path, e)
-        self.log.debug("IPYTHONDIR set to: %s" % new)
+        if self.add_ipython_dir_to_sys_path:
+            str_path = os.path.abspath(new)
+            #sys.path.append(str_path)
+            ensure_dir_exists(new)
+            readme = os.path.join(new, 'README')
+            readme_src = os.path.join(get_ipython_package_dir(), u'config', u'profile', 'README')
+            if not os.path.exists(readme) and os.path.exists(readme_src):
+                shutil.copy(readme_src, readme)
+            for d in ('extensions', 'nbextensions'):
+                path = os.path.join(new, d)
+                try:
+                    ensure_dir_exists(path)
+                except OSError as e:
+                    # this will not be EEXIST
+                    self.log.error("couldn't create path %s: %s", path, e)
+            self.log.debug("IPYTHONDIR set to: %s" % new)
 
     def load_config_file(self, suppress_errors=IPYTHON_SUPPRESS_CONFIG_ERRORS):
         """Load the config file.