fix: Throw when using custom level formatters with multiple transports (

pinojs#1353)

docs/api.md

@@ -293,6 +293,8 @@ Changes the shape of the log level. The default shape is `{ level: number }`.
 The function takes two arguments, the label of the level (e.g. `'info'`)
 and the numeric value (e.g. `30`).
 
+ps: The log level cannot be customized when using multiple transports
+
 ```js
 const formatters = {
   level (label, number) {

lib/tools.js

@@ -409,6 +409,9 @@ function createArgsNormalizer (defaultOptions) {
       if (opts.transport instanceof SonicBoom || opts.transport.writable || opts.transport._writableState) {
         throw Error('option.transport do not allow stream, please pass to option directly. e.g. pino(transport)')
       }
+      if (opts.transport.targets && opts.transport.targets.length && opts.formatters && typeof opts.formatters.level === 'function') {
+        throw Error('option.transport.targets do not allow custom level formatters')
+      }
       stream = transport({ caller, ...opts.transport })
     }
     opts = Object.assign({}, defaultOptions, opts)

test/formatters.test.js

@@ -335,3 +335,30 @@ test('formatter with transport', async ({ match, equal }) => {
     nested: { object: true }
   })
 })
+
+test('throws when custom level formatter is used with transport.targets', async ({ throws }) => {
+  const destination = join(
+    os.tmpdir(),
+    '_' + Math.random().toString(36).substr(2, 9)
+  )
+
+  throws(() => {
+    pino({
+      formatters: {
+        level (label) {
+          return label
+        }
+      },
+      transport: {
+        targets: [
+          {
+            target: 'pino/file',
+            options: { destination }
+          }
+        ]
+      }
+    }
+    )
+  },
+  Error('option.transport.targets do not allow custom level formatters'))
+})