Fix opentracing shim references

CHANGELOG.md

@@ -31,6 +31,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   ([#2145](https://github.com/open-telemetry/opentelemetry-python/pull/2145))
 - Add `schema_url` to `TracerProvider.get_tracer`
   ([#2154](https://github.com/open-telemetry/opentelemetry-python/pull/2154))
+- Fix parental trace relationship for opentracing `follows_from` reference
+  ([#2180](https://github.com/open-telemetry/opentelemetry-python/pull/2180))
 
 ## [1.5.0-0.24b0](https://github.com/open-telemetry/opentelemetry-python/releases/tag/v1.5.0-0.24b0) - 2021-08-26
 

shim/opentelemetry-opentracing-shim/src/opentelemetry/shim/opentracing_shim/__init__.py

@@ -592,7 +592,10 @@ def start_active_span(
 
         current_span = get_current_span()
 
-        if child_of is None and current_span is not INVALID_SPAN_CONTEXT:
+        if (
+            child_of is None
+            and current_span.get_span_context() is not INVALID_SPAN_CONTEXT
+        ):
             child_of = SpanShim(None, None, current_span)
 
         span = self.start_span(
@@ -649,12 +652,20 @@ def start_span(
         if isinstance(parent, OtelSpanContext):
             parent = NonRecordingSpan(parent)
 
-        parent_span_context = set_span_in_context(parent)
-
         links = []
+        valid_links = []
         if references:
             for ref in references:
                 links.append(Link(ref.referenced_context.unwrap()))
+                if ref.referenced_context.unwrap() is not INVALID_SPAN_CONTEXT:
+                    valid_links.append(ref)
+
+        if valid_links and parent is None:
+            parent = NonRecordingSpan(
+                valid_links[0].referenced_context.unwrap()
+            )
+
+        parent_span_context = set_span_in_context(parent)
 
         # The OpenTracing API expects time values to be `float` values which
         # represent the number of seconds since the epoch. OpenTelemetry

shim/opentelemetry-opentracing-shim/tests/test_shim.py

@@ -389,6 +389,24 @@ def test_references(self):
                     parent.context.unwrap(),
                 )
 
+    def test_follows_from_references(self):
+        """Test span creation using the `references` argument with a follows from relationship."""
+
+        with self.shim.start_span("ParentSpan") as parent:
+            ref = opentracing.follows_from(parent.context)
+
+        with self.shim.start_active_span(
+            "FollowingSpan", references=[ref]
+        ) as child:
+            self.assertEqual(
+                child.span.unwrap().links[0].context,
+                parent.context.unwrap(),
+            )
+            self.assertEqual(
+                child.span.unwrap().parent,
+                parent.context.unwrap(),
+            )
+
     def test_set_operation_name(self):
         """Test `set_operation_name()` method."""