Revert "ref(flags): register LD hook in setup instead of init, and don't chec…" (#3900)

Mutating a class attribute on `__init__` violates encapsulation and will lead to strange errors.  We need to rethink how we want to implement this before we merge any code.

A simple reproduction of the issue:

```python
>>> class X:
...     y = 0
...     def __init__(self, z):
...         self.__class__.y = z
... 
>>> a = X(1)
>>> b = X(2)
>>> X.y
2
>>> a.y
2
>>> b.y
2
```

Reverts #3890

This reverts commit c3516db.

Co-authored-by: Anton Pirker <[email protected]>

Author: cmanallen

sentry_sdk/integrations/launchdarkly.py

@@ -20,27 +20,27 @@
 
 class LaunchDarklyIntegration(Integration):
     identifier = "launchdarkly"
-    _ld_client = None  # type: LDClient | None
 
     def __init__(self, ld_client=None):
         # type: (LDClient | None) -> None
         """
         :param client: An initialized LDClient instance. If a client is not provided, this
             integration will attempt to use the shared global instance.
         """
-        self.__class__._ld_client = ld_client
-
-    @staticmethod
-    def setup_once():
-        # type: () -> None
         try:
-            client = LaunchDarklyIntegration._ld_client or ldclient.get()
+            client = ld_client or ldclient.get()
         except Exception as exc:
             raise DidNotEnable("Error getting LaunchDarkly client. " + repr(exc))
 
+        if not client.is_initialized():
+            raise DidNotEnable("LaunchDarkly client is not initialized.")
+
         # Register the flag collection hook with the LD client.
         client.add_hook(LaunchDarklyHook())
 
+    @staticmethod
+    def setup_once():
+        # type: () -> None
         scope = sentry_sdk.get_current_scope()
         scope.add_error_processor(flag_error_processor)
 

tests/integrations/launchdarkly/test_launchdarkly.py

@@ -183,21 +183,22 @@ async def runner():
     }
 
 
-def test_launchdarkly_integration_did_not_enable(sentry_init, uninstall_integration):
-    """
-    Setup should fail when using global client and ldclient.set_config wasn't called.
-
-    We're accessing ldclient internals to set up this test, so it might break if launchdarkly's
-    implementation changes.
-    """
-
+def test_launchdarkly_integration_did_not_enable(monkeypatch):
+    # Client is not passed in and set_config wasn't called.
+    # TODO: Bad practice to access internals like this. We can skip this test, or remove this
+    #  case entirely (force user to pass in a client instance).
     ldclient._reset_client()
     try:
         ldclient.__lock.lock()
         ldclient.__config = None
     finally:
         ldclient.__lock.unlock()
 
-    uninstall_integration(LaunchDarklyIntegration.identifier)
     with pytest.raises(DidNotEnable):
-        sentry_init(integrations=[LaunchDarklyIntegration()])
+        LaunchDarklyIntegration()
+
+    # Client not initialized.
+    client = LDClient(config=Config("sdk-key"))
+    monkeypatch.setattr(client, "is_initialized", lambda: False)
+    with pytest.raises(DidNotEnable):
+        LaunchDarklyIntegration(ld_client=client)