Make SpanProcessor.on_start accept parent Context (#1251)

* context from Tracer.start_span is passed through to the SpanProcessor
* fix linting issue in falcon test app when linting with eachdist script
* fix global error handler test as it read installed extensions
* reset global Configuration object state after tests were run

exporter/opentelemetry-exporter-datadog/CHANGELOG.md

@@ -2,6 +2,9 @@
 
 ## Unreleased
 
+ - Make `SpanProcessor.on_start` accept parent Context
+  ([#1251](https://github.com/open-telemetry/opentelemetry-python/pull/1251))
+
 ## Version 0.14b0
 
 Released 2020-10-13

exporter/opentelemetry-exporter-datadog/src/opentelemetry/exporter/datadog/spanprocessor.py

@@ -17,7 +17,7 @@ import logging
 import threading
 import typing
 
-from opentelemetry.context import attach, detach, set_value
+from opentelemetry.context import Context, attach, detach, set_value
 from opentelemetry.sdk.trace import Span, SpanProcessor
 from opentelemetry.sdk.trace.export import SpanExporter
 from opentelemetry.trace import INVALID_TRACE_ID
@@ -81,7 +81,9 @@ class DatadogExportSpanProcessor(SpanProcessor):
         self.done = False
         self.worker_thread.start()
 
-    def on_start(self, span: Span) -> None:
+    def on_start(
+        self, span: Span, parent_context: typing.Optional[Context] = None
+    ) -> None:
         ctx = span.get_span_context()
         trace_id = ctx.trace_id
 

exporter/opentelemetry-exporter-datadog/tests/test_datadog_exporter.py

@@ -21,6 +21,7 @@ from unittest import mock
 from ddtrace.internal.writer import AgentWriter
 
 from opentelemetry import trace as trace_api
+from opentelemetry.context import Context
 from opentelemetry.exporter import datadog
 from opentelemetry.sdk import trace
 from opentelemetry.sdk.trace import Resource, sampling
@@ -482,6 +483,21 @@ class TestDatadogSpanExporter(unittest.TestCase):
 
         tracer_provider.shutdown()
 
+    def test_span_processor_accepts_parent_context(self):
+        span_processor = mock.Mock(
+            wraps=datadog.DatadogExportSpanProcessor(self.exporter)
+        )
+        tracer_provider = trace.TracerProvider()
+        tracer_provider.add_span_processor(span_processor)
+        tracer = tracer_provider.get_tracer(__name__)
+
+        context = Context()
+        span = tracer.start_span("foo", context=context)
+
+        span_processor.on_start.assert_called_once_with(
+            span, parent_context=context
+        )
+
     def test_origin(self):
         context = trace_api.SpanContext(
             trace_id=0x000000000000000000000000DEADBEEF,