mypy: Prohibit unreachable code.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

zulip/integrations/codebase/zulip_codebase_config.py

@@ -1,3 +1,5 @@
+from typing import Optional
+
 # Change these values to configure authentication for your codebase account
 # Note that this is the Codebase API Username, found in the Settings page
 # for your account
@@ -23,14 +25,14 @@ ZULIP_TICKETS_STREAM_NAME = "tickets"
 
 # If properly installed, the Zulip API should be in your import
 # path, but if not, set a custom path below
-ZULIP_API_PATH = None
+ZULIP_API_PATH: Optional[str] = None
 
 # Set this to your Zulip API server URI
 ZULIP_SITE = "https://zulip.example.com"
 
 # If you wish to log to a file rather than stdout/stderr,
 # please fill this out your desired path
-LOG_FILE = None
+LOG_FILE: Optional[str] = None
 
 # This file is used to resume this mirror in case the script shuts down.
 # It is required and needs to be writeable.

zulip/integrations/codebase/zulip_codebase_mirror

@@ -293,8 +293,7 @@ def check_permissions() -> None:
         sys.stderr.write(str(e))
 
 if __name__ == "__main__":
-    if not isinstance(config.RESUME_FILE, str):
-        sys.stderr.write("RESUME_FILE path not given; refusing to continue")
+    assert isinstance(config.RESUME_FILE, str), "RESUME_FILE path not given; refusing to continue"
     check_permissions()
     if config.LOG_FILE:
         logging.basicConfig(filename=config.LOG_FILE, level=logging.WARNING)