Removing get_current_span from Tracer and TracerProvider

After discussion in the SIG, we decided to remove the
legacy get_current_span APIs from Tracer and TracerProvider
to reduce long-term confusion of how to idiomatically retrieve
the span.

opentelemetry-api/src/opentelemetry/trace/__init__.py

@@ -272,18 +272,6 @@ class Tracer(abc.ABC):
     # This is the default behavior when creating spans.
     CURRENT_SPAN = DefaultSpan(INVALID_SPAN_CONTEXT)
 
-    @abc.abstractmethod
-    def get_current_span(self) -> "Span":  # noqa
-        """Gets the currently active span from the context.
-
-        If there is no current span, return a placeholder span with an invalid
-        context.
-
-        Returns:
-            The currently active :class:`.Span`, or a placeholder span with an
-            invalid :class:`.SpanContext`.
-        """
-
     @abc.abstractmethod
     def start_span(
         self,
@@ -355,11 +343,11 @@ def start_as_current_span(
 
             with tracer.start_as_current_span("one") as parent:
                 parent.add_event("parent's event")
-                with tracer.start_as_current_span("two") as child:
+                with trace.start_as_current_span("two") as child:
                     child.add_event("child's event")
-                    tracer.get_current_span()  # returns child
-                tracer.get_current_span()      # returns parent
-            tracer.get_current_span()          # returns previously active span
+                    trace.get_current_span()  # returns child
+                trace.get_current_span()      # returns parent
+            trace.get_current_span()          # returns previously active span
 
         This is a convenience method for creating spans attached to the
         tracer's context. Applications that need more control over the span
@@ -413,10 +401,6 @@ class DefaultTracer(Tracer):
     All operations are no-op.
     """
 
-    def get_current_span(self) -> "Span":  # noqa
-        # pylint: disable=no-self-use
-        return INVALID_SPAN
-
     def start_span(
         self,
         name: str,

opentelemetry-api/tests/trace/test_tracer.py

@@ -21,10 +21,6 @@ class TestTracer(unittest.TestCase):
     def setUp(self):
         self.tracer = trace.DefaultTracer()
 
-    def test_get_current_span(self):
-        span = self.tracer.get_current_span()
-        self.assertIsInstance(span, trace.Span)
-
     def test_start_span(self):
         with self.tracer.start_span("") as span:
             self.assertIsInstance(span, trace.Span)

opentelemetry-sdk/src/opentelemetry/sdk/trace/__init__.py

@@ -593,9 +593,6 @@ def __init__(
         self.source = source
         self.instrumentation_info = instrumentation_info
 
-    def get_current_span(self):  # pylint: disable
-        return self.source.get_current_span()
-
     def start_as_current_span(
         self,
         name: str,
@@ -618,7 +615,7 @@ def start_span(  # pylint: disable=too-many-locals
         set_status_on_exception: bool = True,
     ) -> trace_api.Span:
         if parent is Tracer.CURRENT_SPAN:
-            parent = self.get_current_span()
+            parent = trace_api.get_current_span()
 
         parent_context = parent
         if isinstance(parent_context, trace_api.Span):

opentelemetry-sdk/tests/trace/test_trace.py

@@ -211,24 +211,6 @@ def test_span_processor_for_source(self):
             span2.span_processor, tracer_provider._active_span_processor
         )
 
-    def test_get_current_span_multiple_tracers(self):
-        """In the case where there are multiple tracers,
-        get_current_span will return the same active span
-        for both tracers.
-        """
-        tracer_1 = new_tracer()
-        tracer_2 = new_tracer()
-        root = tracer_1.start_span("root")
-        with tracer_1.use_span(root, True):
-            self.assertIs(tracer_1.get_current_span(), root)
-            self.assertIs(tracer_2.get_current_span(), root)
-            self.assertIs(trace_api.get_current_span(), root)
-
-        # outside of the loop, both should not reference a span.
-        self.assertIs(tracer_1.get_current_span(), None)
-        self.assertIs(tracer_2.get_current_span(), None)
-        self.assertIs(trace_api.get_current_span(), None)
-
     def test_start_span_implicit(self):
         tracer = new_tracer()
 
@@ -271,7 +253,7 @@ def test_start_span_implicit(self):
 
             self.assertIsNotNone(child.end_time)
 
-        self.assertIsNone(tracer.get_current_span())
+        self.assertIsNone(trace_api.get_current_span())
         self.assertIsNotNone(root.end_time)
 
     def test_start_span_explicit(self):
@@ -599,7 +581,7 @@ def event_formatter():
             self.assertEqual(root.events[4].timestamp, now)
 
     def test_invalid_event_attributes(self):
-        self.assertIsNone(self.tracer.get_current_span())
+        self.assertIsNone(trace_api.get_current_span())
 
         with self.tracer.start_as_current_span("root") as root:
             root.add_event("event0", {"attr1": True, "attr2": ["hi", False]})