fix: Fix sample decision propagation via headers

sentry_sdk/tracing.py

@@ -583,22 +583,23 @@ def _set_initial_sampling_decision(self, sampling_context):
         decision, `traces_sample_rate` will be used.
         """
 
+        # if the user has forced a sampling decision by passing a `sampled`
+        # value when starting the transaction, go with that
+        if self.sampled is not None:
+            return
+
         hub = self.hub or sentry_sdk.Hub.current
         client = hub.client
-        options = (client and client.options) or {}
         transaction_description = "{op}transaction <{name}>".format(
             op=("<" + self.op + "> " if self.op else ""), name=self.name
         )
 
-        # nothing to do if there's no client or if tracing is disabled
-        if not client or not has_tracing_enabled(options):
+        # nothing to do if there's no client
+        if not client:
             self.sampled = False
             return
 
-        # if the user has forced a sampling decision by passing a `sampled`
-        # value when starting the transaction, go with that
-        if self.sampled is not None:
-            return
+        options = client.options
 
         # we would have bailed already if neither `traces_sampler` nor
         # `traces_sample_rate` were defined, so one of these should work; prefer
@@ -662,16 +663,6 @@ def _set_initial_sampling_decision(self, sampling_context):
             )
 
 
-def has_tracing_enabled(options):
-    # type: (Dict[str, Any]) -> bool
-    """
-    Returns True if either traces_sample_rate or traces_sampler is
-    non-zero/defined, False otherwise.
-    """
-
-    return bool(options.get("traces_sample_rate") or options.get("traces_sampler"))
-
-
 def _is_valid_sample_rate(rate):
     # type: (Any) -> bool
     """

setup.py

@@ -18,7 +18,7 @@ def get_file_text(file_name):
     with open(os.path.join(here, file_name)) as in_file:
         return in_file.read()
 
-    
+
 setup(
     name="sentry-sdk",
     version="0.19.4",
@@ -31,7 +31,7 @@ def get_file_text(file_name):
     },
     description="Python client for Sentry (https://sentry.io)",
     long_description=get_file_text("README.md"),
-    long_description_content_type='text/markdown',
+    long_description_content_type="text/markdown",
     packages=find_packages(exclude=("tests", "tests.*")),
     # PEP 561
     package_data={"sentry_sdk": ["py.typed"]},

tests/tracing/test_integration_tests.py

@@ -47,12 +47,15 @@ def test_basic(sentry_init, capture_events, sample_rate):
 
 
 @pytest.mark.parametrize("sampled", [True, False, None])
-def test_continue_from_headers(sentry_init, capture_events, sampled):
-    sentry_init(traces_sample_rate=1.0)
+@pytest.mark.parametrize(
+    "sample_rate", [0.0, 1.0]
+)  # ensure sampling decision is actually passed along via headers
+def test_continue_from_headers(sentry_init, capture_events, sampled, sample_rate):
+    sentry_init(traces_sample_rate=sample_rate)
     events = capture_events()
 
     # make a parent transaction (normally this would be in a different service)
-    with start_transaction(name="hi"):
+    with start_transaction(name="hi", sampled=True if sample_rate == 0 else None):
         with start_span() as old_span:
             old_span.sampled = sampled
             headers = dict(Hub.current.iter_trace_propagation_headers())
@@ -84,7 +87,7 @@ def test_continue_from_headers(sentry_init, capture_events, sampled):
             scope.transaction = "ho"
         capture_message("hello")
 
-    if sampled is False:
+    if sampled is False or (sample_rate == 0 and sampled is None):
         trace1, message = events
 
         assert trace1["transaction"] == "hi"