feat: add Tracer#context_with_span convenience method

api/lib/opentelemetry/trace/tracer.rb

@@ -21,6 +21,15 @@ def current_span(context = Context.current)
         context.value(CURRENT_SPAN_KEY) || Span::INVALID
       end
 
+      # Returns a context containing the span, derived from the optional parent
+      # context, or the current context if one was not provided.
+      #
+      # @param [optional Context] context The context to use as the parent for
+      #  the returned context
+      def context_with_span(span, context = Context.current)
+        context.set_value(CURRENT_SPAN_KEY, span)
+      end
+
       # This is a helper for the default use-case of extending the current trace with a span.
       #
       # With this helper:

api/test/opentelemetry/trace/tracer_test.rb

@@ -161,4 +161,20 @@ def start_span(*)
       _(span.context).wont_equal(invalid_span_context)
     end
   end
+
+  describe '#context_with_span' do
+    it 'returns a context containing span' do
+      span = tracer.start_span('test')
+      ctx = tracer.context_with_span(span)
+      _(tracer.current_span(ctx)).must_equal(span)
+    end
+
+    it 'returns a context containing span' do
+      parent_ctx = OpenTelemetry::Context.empty.set_value('foo', 'bar')
+      span = tracer.start_span('test')
+      ctx = tracer.context_with_span(span, parent_ctx)
+      _(tracer.current_span(ctx)).must_equal(span)
+      _(ctx.value('foo')).must_equal('bar')
+    end
+  end
 end