Move parsing for the fine-grained flag into the main arg parsing code

mypy/dmypy_server.py

@@ -86,13 +86,11 @@ class Server:
     def __init__(self, flags: List[str]) -> None:
         """Initialize the server with the desired mypy flags."""
         self.saved_cache = {}  # type: mypy.build.SavedCache
-        if '--experimental' in flags:
-            self.fine_grained = True
-            self.fine_grained_initialized = False
-            flags.remove('--experimental')
-        else:
-            self.fine_grained = False
-        sources, options = mypy.main.process_options(['-i'] + flags, False)
+        self.fine_grained_initialized = False
+        sources, options = mypy.main.process_options(['-i'] + flags,
+                                                     require_targets=False,
+                                                     server_options=True)
+        self.fine_grained = options.fine_grained_incremental
         if sources:
             sys.exit("dmypy: start/restart does not accept sources")
         if options.report_dirs:

mypy/main.py

@@ -206,7 +206,8 @@ def invert_flag_name(flag: str) -> str:
 
 
 def process_options(args: List[str],
-                    require_targets: bool = True
+                    require_targets: bool = True,
+                    server_options: bool = False,
                     ) -> Tuple[List[BuildSource], Options]:
     """Parse command line arguments."""
 
@@ -389,6 +390,9 @@ def add_invertible_flag(flag: str,
     parser.add_argument('--no-fast-parser', action='store_true',
                         dest='special-opts:no_fast_parser',
                         help=argparse.SUPPRESS)
+    if server_options:
+        parser.add_argument('--experimental', action='store_true', dest='fine_grained_incremental',
+                            help="enable fine-grained incremental mode")
 
     report_group = parser.add_argument_group(
         title='report generation',

mypy/options.py

@@ -141,6 +141,7 @@ def __init__(self) -> None:
         self.debug_cache = False
         self.quick_and_dirty = False
         self.skip_version_check = False
+        self.fine_grained_incremental = False
 
         # Paths of user plugins
         self.plugins = []  # type: List[str]