catch potential write errors on fatal flush sync (#740)

* Add forceFlushOnFatal flag

* Remove unused line

* Do nothing on error

* Update lib/levels.js

Co-Authored-By: David Mark Clements <david.mark.clements@gmail.com>

* Remove once

lib/levels.js

@@ -24,7 +24,11 @@ const levelMethods = {
     const stream = this[streamSym]
     logFatal.call(this, ...args)
     if (typeof stream.flushSync === 'function') {
-      stream.flushSync()
+      try {
+        stream.flushSync()
+      } catch (e) {
+        // https://github.com/pinojs/pino/pull/740#discussion_r346788313
+      }
     }
   },
   error: genLog(levels.error),

test/levels.test.js

@@ -417,3 +417,16 @@ test('fatal method sync-flushes the destination if sync flushing is available',
     instance.fatal('this is fatal')
   })
 })
+
+test('fatal method should call async when sync-flushing fails', ({ equal, fail, doesNotThrow, plan }) => {
+  plan(2)
+  const messages = [
+    'this is fatal 1'
+  ]
+  const stream = sink((result) => equal(result.msg, messages.shift()))
+  stream.flushSync = () => { throw new Error('Error') }
+  stream.flush = () => fail('flush should be called')
+
+  const instance = pino(stream)
+  doesNotThrow(() => instance.fatal(messages[0]))
+})