fix(apm): Continuation of a trace from another span should use its span id as the parent span id (#572)

Correction based on what I see on the JS SDK:

https://github.com/getsentry/sentry-javascript/blob/01cac4ff6c09d7cf4b5e9d6cf595b095a8d036f3/packages/apm/src/span.ts#L202-L207

Author: dashed

sentry_sdk/tracing.py

@@ -205,7 +205,8 @@ def continue_from_headers(cls, headers):
         parent = cls.from_traceparent(headers.get("sentry-trace"))
         if parent is None:
             return cls()
-        return parent.new_span(same_process_as_parent=False)
+        parent.same_process_as_parent = False
+        return parent
 
     def iter_headers(self):
         # type: () -> Generator[Tuple[str, str], None, None]
@@ -236,7 +237,7 @@ def from_traceparent(cls, traceparent):
         else:
             sampled = None
 
-        return cls(trace_id=trace_id, span_id=span_id, sampled=sampled)
+        return cls(trace_id=trace_id, parent_span_id=span_id, sampled=sampled)
 
     def to_traceparent(self):
         # type: () -> str

tests/test_tracing.py

@@ -59,6 +59,9 @@ def test_continue_from_headers(sentry_init, capture_events, sampled):
     assert span is not None
     assert span.sampled == sampled
     assert span.trace_id == old_span.trace_id
+    assert span.same_process_as_parent is False
+    assert span.parent_span_id == old_span.span_id
+    assert span.span_id != old_span.span_id
 
     with Hub.current.start_span(span):
         with Hub.current.configure_scope() as scope: