fix(spotlight): More defensive Django spotlight middleware injection

Turns out `settings.MIDDLEWARE` does not have to be a `list`. This causes issues as not all iterables support appending items to them. This PR leverages `itertools.chain` along with `type(settings.MIDDLEWARE)` to extend the middleware list while keeping its original type. It also adds a try-except block around the injection code to make sure it doesn't block anything further down in the unexpected case that it fails.

Author: BYK

sentry_sdk/spotlight.py

@@ -5,6 +5,8 @@
 import urllib.error
 import urllib3
 
+from itertools import chain
+
 from typing import TYPE_CHECKING
 
 if TYPE_CHECKING:
@@ -18,6 +20,7 @@
 
 
 DEFAULT_SPOTLIGHT_URL = "http://localhost:8969/stream"
+DJANGO_SPOTLIGHT_MIDDLEWARE_PATH = "sentry_sdk.spotlight.SpotlightMiddleware"
 
 
 class SpotlightClient:
@@ -112,9 +115,18 @@ def setup_spotlight(options):
     else:
         return None
 
-    if settings is not None and env_to_bool(
-        os.environ.get("SENTRY_SPOTLIGHT_ON_ERROR", "1")
+    if (
+        settings is not None
+        and settings.DEBUG
+        and env_to_bool(os.environ.get("SENTRY_SPOTLIGHT_ON_ERROR", "1"))
     ):
-        settings.MIDDLEWARE.append("sentry_sdk.spotlight.SpotlightMiddleware")
+        try:
+            middleware = settings.MIDDLEWARE
+            if DJANGO_SPOTLIGHT_MIDDLEWARE_PATH not in middleware:
+                settings.MIDDLEWARE = type(middleware)(
+                    chain(middleware, (DJANGO_SPOTLIGHT_MIDDLEWARE_PATH,))
+                )
+        except Exception as err:
+            logger.error("Cannot inject Spotlight middleware", exc_info=err)
 
     return SpotlightClient(url)