Fixed stream metadata loss during prettification

lib/tools.js

@@ -178,6 +178,7 @@ function prettifierMetaWrapper (pretty, dest) {
         return
       }
       warned = true
+      setMetadataProps(dest, this)
       dest.write(pretty(Object.assign({
         level: 40, // warn
         msg: 'pino.final with prettyPrint does not support flushing',
@@ -237,6 +238,8 @@ function prettifierMetaWrapper (pretty, dest) {
 
       const formatted = pretty(typeof redact === 'function' ? redact(obj) : obj)
       if (formatted === undefined) return
+
+      setMetadataProps(dest, this)
       dest.write(formatted)
     }
   }
@@ -351,6 +354,16 @@ function stringify (obj) {
   }
 }
 
+function setMetadataProps (dest, that) {
+  if (dest[needsMetadataGsym] === true) {
+    dest.lastLevel = that.lastLevel
+    dest.lastMsg = that.lastMsg
+    dest.lastObj = that.lastObj
+    dest.lastTime = that.lastTime
+    dest.lastLogger = that.lastLogger
+  }
+}
+
 module.exports = {
   noop,
   buildSafeSonicBoom,

test/pretty.test.js

@@ -272,3 +272,41 @@ test('works as expected with an object with the msg prop', async ({ isNot }) =>
   await once(child, 'close')
   isNot(actual.match(/\(123456 on abcdefghijklmnopqr\): hello/), null)
 })
+
+test('should not lose stream metadata for streams with `needsMetadataGsym` flag', async ({ isNot }) => {
+  const dest = new Writable({
+    objectMode: true,
+    write () {
+      isNot(typeof this.lastLevel === 'undefined', true)
+      isNot(typeof this.lastMsg === 'undefined', true)
+      isNot(typeof this.lastObj === 'undefined', true)
+      isNot(typeof this.lastTime === 'undefined', true)
+      isNot(typeof this.lastLogger === 'undefined', true)
+    }
+  })
+
+  dest[pino.symbols.needsMetadataGsym] = true
+
+  const log = pino({
+    prettyPrint: true
+  }, dest)
+  log.info('foo')
+})
+
+test('should not add stream metadata for streams without `needsMetadataGsym` flag', async ({ is }) => {
+  const dest = new Writable({
+    objectMode: true,
+    write () {
+      is(typeof this.lastLevel === 'undefined', true)
+      is(typeof this.lastMsg === 'undefined', true)
+      is(typeof this.lastObj === 'undefined', true)
+      is(typeof this.lastTime === 'undefined', true)
+      is(typeof this.lastLogger === 'undefined', true)
+    }
+  })
+
+  const log = pino({
+    prettyPrint: true
+  }, dest)
+  log.info('foo')
+})