fix(resources): wait for async attributes for detecting resources

CHANGELOG.md

@@ -21,6 +21,7 @@ For experimental package changes, see the [experimental CHANGELOG](experimental/
 * fix(resources): prevent circular import (resource -> detector -> resource -> ...) [#4653](https://github.com/open-telemetry/opentelemetry-js/pull/4653) @pichlermarc
   * fixes a circular import warning which would appear in rollup when bundling `@opentelemetry/resources`
 * fix(exporter-metrics-otlp-grpc): add explicit otlp-exporter-base dependency to exporter-metrics-otlp-grpc [#4678](https://github.com/open-telemetry/opentelemetry-js/pull/4678) @AkselAllas
+* fix(resources) wait for async attributes for detecting resources [#4687](https://github.com/open-telemetry/opentelemetry-js/pull/4687) @ziolekjj
 
 ### :books: (Refine Doc)
 

packages/opentelemetry-resources/src/detect-resources.ts

@@ -70,6 +70,9 @@ export const detectResourcesSync = (
         if (isPromiseLike<Resource>(resourceOrPromise)) {
           const createPromise = async () => {
             const resolvedResource = await resourceOrPromise;
+            if (resolvedResource.waitForAsyncAttributes) {
+              await resolvedResource.waitForAsyncAttributes();
+            }
             return resolvedResource.attributes;
           };
           resource = new Resource({}, createPromise());

packages/opentelemetry-resources/test/detect-resources.test.ts

@@ -28,7 +28,10 @@ describe('detectResourcesSync', () => {
   it('handles resource detectors which return Promise<Resource>', async () => {
     const detector: Detector = {
       async detect() {
-        return new Resource({ sync: 'fromsync' });
+        return new Resource(
+          { sync: 'fromsync' },
+          Promise.resolve({ async: 'fromasync' }).then(attrs => attrs)
+        );
       },
     };
     const resource = detectResourcesSync({
@@ -38,6 +41,7 @@ describe('detectResourcesSync', () => {
     await resource.waitForAsyncAttributes?.();
     assert.deepStrictEqual(resource.attributes, {
       sync: 'fromsync',
+      async: 'fromasync',
     });
   });