Add service_version option support (#122)

Adds support for configuring a service version in tracer options, which
can be used for tracking service deployments and their performance regressions.

lib/span.ex

@@ -16,6 +16,7 @@ defmodule Spandex.Span do
     :private,
     :resource,
     :service,
+    :service_version,
     :services,
     :sql_query,
     :start,
@@ -37,6 +38,7 @@ defmodule Spandex.Span do
           private: Keyword.t(),
           resource: atom() | String.t(),
           service: atom(),
+          service_version: String.t() | nil,
           services: Keyword.t() | nil,
           sql_query: Keyword.t() | nil,
           start: Spandex.timestamp(),
@@ -57,6 +59,7 @@ defmodule Spandex.Span do
                  private: :keyword,
                  resource: [:atom, :string],
                  service: :atom,
+                 service_version: :string,
                  services: :keyword,
                  sql_query: :keyword,
                  start: :integer,

lib/tracer.ex

@@ -51,6 +51,7 @@ defmodule Spandex.Tracer do
                    service: :atom,
                    disabled?: :boolean,
                    env: :string,
+                   service_version: :string,
                    services: {:keyword, :atom},
                    strategy: :atom,
                    sender: :atom,
@@ -68,6 +69,7 @@ defmodule Spandex.Tracer do
                    sender:
                      "Once a trace is complete, it is sent using this module. Defaults to the `default_sender/0` of the selected adapter",
                    service: "The default service name to use for spans declared without a service",
+                   service_version: "The version of the service, used for tracking deployments.",
                    disabled?: "Allows for wholesale disabling a tracer",
                    env: "A name used to identify the environment name, e.g `prod` or `development`",
                    services: "A mapping of service name to the default span types.",

test/spandex_test.exs

@@ -25,6 +25,7 @@ defmodule Spandex.Test.SpandexTest do
 
   @span_opts [
     service: :test_service,
+    service_version: "v1",
     resource: "test_resource"
   ]
 
@@ -91,11 +92,11 @@ defmodule Spandex.Test.SpandexTest do
       assert {:error, :disabled} = Spandex.start_span("root_span", :disabled)
     end
 
-    test "inherits service and resource from parent span if not specified" do
+    test "inherits service, service_version and resource from parent span if not specified" do
       opts = @base_opts ++ @span_opts
       assert {:ok, %Trace{id: _trace_id}} = Spandex.start_trace("root_span", opts)
       assert {:ok, %Span{} = span} = Spandex.start_span("span_name", @base_opts)
-      assert %Span{name: "span_name", service: :test_service, resource: "test_resource"} = span
+      assert %Span{name: "span_name", service: :test_service, service_version: "v1", resource: "test_resource"} = span
     end
 
     test "returns an error if invalid options are specified" do