fix(tracing): lazy importing asyncio should not reset existing trace context [backport 2.7]

ddtrace/_trace/provider.py

@@ -113,7 +113,6 @@ class DefaultContextProvider(BaseContextProvider, DatadogContextMixin):
     def __init__(self):
         # type: () -> None
         super(DefaultContextProvider, self).__init__()
-        _DD_CONTEXTVAR.set(None)
 
     def _has_active_context(self):
         # type: () -> bool

releasenotes/notes/fix-asyncio-context-reset-6283f01dc7d46dc4.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    This fix resolves an issue where importing ``asyncio`` after a trace has already been started will reset the currently active span.

tests/conftest.py

@@ -16,12 +16,14 @@
 from typing import Generator  # noqa:F401
 from typing import Tuple  # noqa:F401
 from unittest import mock
+import warnings
 
 from _pytest.runner import call_and_report
 from _pytest.runner import pytest_runtest_protocol as default_pytest_runtest_protocol
 import pytest
 
 import ddtrace
+from ddtrace._trace.provider import _DD_CONTEXTVAR
 from ddtrace.internal.compat import httplib
 from ddtrace.internal.compat import parse
 from ddtrace.internal.remoteconfig.client import RemoteConfigClient
@@ -67,6 +69,17 @@ def test_spans(tracer):
     container.reset()
 
 
+@pytest.fixture(autouse=True)
+def clear_context_after_every_test():
+    try:
+        yield
+    finally:
+        ctx = _DD_CONTEXTVAR.get()
+        if ctx is not None:
+            warnings.warn(f"Context was not cleared after test, expected None, got {ctx}")
+        _DD_CONTEXTVAR.set(None)
+
+
 @pytest.fixture
 def run_python_code_in_subprocess(tmpdir):
     def _run(code, **kwargs):

tests/contrib/asyncio/test_lazyimport.py

@@ -0,0 +1,18 @@
+import pytest  # noqa: I001
+
+
+@pytest.mark.subprocess()
+def test_lazy_import():
+    import ddtrace.auto  # noqa: F401,I001
+    from ddtrace import tracer  # noqa: I001
+
+    assert tracer.context_provider.active() is None
+    span = tracer.trace("itsatest", service="test", resource="resource", span_type="http")
+    assert tracer.context_provider.active() is span
+
+    # Importing asyncio after starting a trace does not remove the current active span
+    import asyncio  # noqa: F401
+
+    assert tracer.context_provider.active() is span
+    span.finish()
+    assert tracer.context_provider.active() is None