Fix capacity validation

Author: cmanallen

sentry_sdk/tracing.py

@@ -316,7 +316,7 @@ def __init__(
         self._data = {}  # type: Dict[str, Any]
         self._containing_transaction = containing_transaction
         self._flags = {}  # type: Dict[str, bool]
-        self._flags_capacity = 0
+        self._flags_capacity = 3
 
         if hub is not None:
             warnings.warn(
@@ -610,7 +610,7 @@ def set_data(self, key, value):
 
     def set_flag(self, flag, result):
         # type: (str, bool) -> None
-        if len(self._flags) >= self._flags_capacity:
+        if len(self._flags) < self._flags_capacity:
             self._flags[flag] = result
 
     def set_status(self, value):

tests/test_feature_flags.py

@@ -7,6 +7,8 @@
 
 import sentry_sdk
 from sentry_sdk.feature_flags import add_feature_flag, FlagBuffer
+from sentry_sdk import start_span, start_transaction
+from tests.conftest import ApproxDict
 
 
 def test_featureflags_integration(sentry_init, capture_events, uninstall_integration):
@@ -220,3 +222,26 @@ def reader():
     # shared resource. When deepcopying we should have exclusive access to the underlying
     # memory.
     assert error_occurred is False
+
+
+def test_flag_limit(sentry_init, capture_events):
+    sentry_init(traces_sample_rate=1.0)
+
+    events = capture_events()
+
+    with start_transaction(name="hi"):
+        with start_span(op="foo", name="bar"):
+            add_feature_flag("first", True)
+            add_feature_flag("second", True)
+            add_feature_flag("third", True)
+            add_feature_flag("fourth", True)
+
+    (event,) = events
+    assert event["spans"][0]["data"] == ApproxDict(
+        {
+            "flag.evaluation.first": True,
+            "flag.evaluation.second": True,
+            "flag.evaluation.third": True,
+        }
+    )
+    assert "flag.evaluation.fourth" not in event["spans"][0]["data"]