Log Unhandled rejection stack (#113614)

* Refactor state types

* Log the stack trace of unhandled promise rejections

* Revert "Refactor state types"

This reverts commit 6a5123a.

* Fix types

* code review feedback

src/core/server/environment/environment_service.test.ts

@@ -135,6 +135,32 @@ describe('UuidService', () => {
         expect(logger.get('process').warn).not.toHaveBeenCalled();
       });
     });
+
+    describe('unhandledRejection warnings', () => {
+      it('logs warn for an unhandeld promise rejected with an Error', async () => {
+        await service.preboot();
+
+        const err = new Error('something went wrong');
+        process.emit('unhandledRejection', err, new Promise((res, rej) => rej(err)));
+
+        expect(logger.get('process').warn).toHaveBeenCalledTimes(1);
+        expect(loggingSystemMock.collect(logger).warn[0][0]).toMatch(
+          /Detected an unhandled Promise rejection: Error: something went wrong\n.*at /
+        );
+      });
+
+      it('logs warn for an unhandeld promise rejected with a string', async () => {
+        await service.preboot();
+
+        const err = 'something went wrong';
+        process.emit('unhandledRejection', err, new Promise((res, rej) => rej(err)));
+
+        expect(logger.get('process').warn).toHaveBeenCalledTimes(1);
+        expect(loggingSystemMock.collect(logger).warn[0][0]).toMatch(
+          /Detected an unhandled Promise rejection: "something went wrong"/
+        );
+      });
+    });
   });
 
   describe('#setup()', () => {

src/core/server/environment/environment_service.ts

@@ -54,9 +54,10 @@ export class EnvironmentService {
       this.configService.atPath<PidConfigType>(pidConfigDef.path).pipe(take(1)).toPromise(),
     ]);
 
-    // was present in the legacy `pid` file.
+    // Log unhandled rejections so that we can fix them in preparation for https://github.com/elastic/kibana/issues/77469
     process.on('unhandledRejection', (reason) => {
-      this.log.warn(`Detected an unhandled Promise rejection.\n${reason}`);
+      const message = (reason as Error)?.stack ?? JSON.stringify(reason);
+      this.log.warn(`Detected an unhandled Promise rejection: ${message}`);
     });
 
     process.on('warning', (warning) => {