Add the ability to flush() the LogSink from OptionalLogger and friends (

#19)

package.json

@@ -1,7 +1,7 @@
 {
   "name": "@rocicorp/logger",
   "description": "Logging utilities",
-  "version": "5.0.0",
+  "version": "5.1.0",
   "repository": "github:rocicorp/logger",
   "license": "Apache-2.0",
   "engines": {

src/logger.test.ts

@@ -262,6 +262,15 @@ test('tee logger flush', async () => {
   expect(l3.flushCount).to.equal(1);
 });
 
+test('optional logger flush', async () => {
+  const l1 = new TestLogSinkWithFlush();
+  const logger = new OptionalLoggerImpl(l1);
+
+  expect(l1.flushCount).to.equal(0);
+  await logger.flush();
+  expect(l1.flushCount).to.equal(1);
+});
+
 test('Console logger calls JSON stringify on complex arguments', () => {
   const jsonStringifySpy = sinon.spy(JSON, 'stringify');
   const mockDebug = mockConsoleMethod('debug');

src/logger.ts

@@ -9,6 +9,7 @@ export interface OptionalLogger {
   error?(...args: unknown[]): void;
   info?(...args: unknown[]): void;
   debug?(...args: unknown[]): void;
+  flush?(): Promise<void>;
 }
 
 /**
@@ -59,6 +60,7 @@ export class OptionalLoggerImpl implements OptionalLogger {
   readonly debug?: (...args: unknown[]) => void = undefined;
   readonly info?: (...args: unknown[]) => void = undefined;
   readonly error?: (...args: unknown[]) => void = undefined;
+  readonly flush: () => Promise<void>;
 
   constructor(logSink: LogSink, level: LogLevel = 'info', context?: Context) {
     const impl =
@@ -78,6 +80,8 @@ export class OptionalLoggerImpl implements OptionalLogger {
         this.error = impl('error');
     }
     /* eslint-enable @typescript-eslint/ban-ts-comment, no-fallthrough */
+
+    this.flush = () => logSink.flush?.() ?? Promise.resolve();
   }
 }