Added CLI support for Mypy Plugins

docs/source/command_line.rst

@@ -888,6 +888,11 @@ in developing or debugging mypy internals.
     This flag will invoke the Python debugger when mypy encounters
     a fatal error.
 
+.. option:: --extend-plugins, --ep {MODULE|PLUGIN_FILE} ...
+
+    This flag acts as a supplementary way to pass (a list of) plugins to customize
+    Mypy's type checking approach. See :ref:`extending-mypy` for more details.
+
 .. option:: --show-traceback, --tb
 
     If set, this flag will display a full traceback when mypy

mypy/main.py

@@ -1008,6 +1008,14 @@ def add_invertible_flag(
         title="Advanced options", description="Debug and customize mypy internals."
     )
     internals_group.add_argument("--pdb", action="store_true", help="Invoke pdb on fatal error")
+    internals_group.add_argument(
+        "--extend-plugins",
+        "--ep",
+        type=lambda s: [item.strip() for item in s.split(",")],
+        metavar="{MODULE|PLUGIN_FILE}",
+        dest="special-opts:cli_plugins",
+        help="Include user defined plugins during Mypy's type analysis",
+    )
     internals_group.add_argument(
         "--show-traceback", "--tb", action="store_true", help="Show traceback on fatal error"
     )
@@ -1291,6 +1299,11 @@ def set_strict_flags() -> None:
     special_opts = argparse.Namespace()
     parser.parse_args(args, SplitNamespace(options, special_opts, "special-opts:"))
 
+    # Parse extra plugins passed via cli args
+    if special_opts.cli_plugins:
+        options.plugins.extend(special_opts.cli_plugins)
+        print(special_opts.cli_plugins)
+
     # The python_version is either the default, which can be overridden via a config file,
     # or stored in special_opts and is passed via the command line.
     options.python_version = special_opts.python_version or options.python_version