fix: propagate otel span kind to span.kind tag (#6904)

Since opentelemetry tags always have span kinds defined (and if the
host project doesn't specify it then it defaults to INTERNAL) then let's
propagate that span kind to DD's `span.kind` tag so that it is properly
visible in the UI. Otherwise we are forcing clients to add a redundant
addAttribute if they want to retain the span kind after the trace is
sent to datadog.

Co-authored-by: Piotr Jakubowski <piotrj@gmail.com>

Author: mabdinur

packages/dd-trace/src/opentelemetry/span.js

@@ -10,7 +10,7 @@ const { timeInputToHrTime } = require('@opentelemetry/core')
 const tracer = require('../../')
 const DatadogSpan = require('../opentracing/span')
 const { ERROR_MESSAGE, ERROR_TYPE, ERROR_STACK, IGNORE_OTEL_ERROR } = require('../constants')
-const { SERVICE_NAME, RESOURCE_NAME } = require('../../../../ext/tags')
+const { SERVICE_NAME, RESOURCE_NAME, SPAN_KIND } = require('../../../../ext/tags')
 const kinds = require('../../../../ext/kinds')
 
 const SpanContext = require('./span_context')
@@ -146,7 +146,8 @@ class Span {
       integrationName: parentTracer?._isOtelLibrary ? 'otel.library' : 'otel',
       tags: {
         [SERVICE_NAME]: _tracer._service,
-        [RESOURCE_NAME]: spanName
+        [RESOURCE_NAME]: spanName,
+        [SPAN_KIND]: spanKindNames[kind]
       },
       links
     }, _tracer._debug)

packages/dd-trace/test/opentelemetry/span.spec.js

@@ -17,7 +17,7 @@ const SpanContext = require('../../src/opentelemetry/span_context')
 const { NoopSpanProcessor } = require('../../src/opentelemetry/span_processor')
 
 const { ERROR_MESSAGE, ERROR_STACK, ERROR_TYPE, IGNORE_OTEL_ERROR } = require('../../src/constants')
-const { SERVICE_NAME, RESOURCE_NAME } = require('../../../../ext/tags')
+const { SERVICE_NAME, RESOURCE_NAME, SPAN_KIND } = require('../../../../ext/tags')
 const kinds = require('../../../../ext/kinds')
 const format = require('../../src/format')
 
@@ -235,6 +235,13 @@ describe('OTel Span', () => {
     expect(context._tags[RESOURCE_NAME]).to.equal('name')
   })
 
+  it('should copy span kind to span.kind', () => {
+    const span = makeSpan('name', { kind: api.SpanKind.CONSUMER })
+
+    const context = span._ddSpan.context()
+    expect(context._tags[SPAN_KIND]).to.equal(kinds.CONSUMER)
+  })
+
   it('should expose span context', () => {
     const span = makeSpan('name')