fix(react-native): Copy RN's internal logging for unhandled rejections

packages/plugin-react-native-unhandled-rejection/rejection-handler.js

@@ -18,20 +18,40 @@ module.exports = {
           severityReason: { type: 'unhandledPromiseRejection' }
         }, 'promise rejection tracking', 1)
         client._notify(event)
-        // adding our own onUnhandled callback means the default log message doesn't happen, so make it happen here
-        if (typeof __DEV__ !== 'undefined' && __DEV__) logError(id, error)
+        // adding our own onUnhandled callback means the default handler doesn't get called, so make it happen here
+        if (typeof __DEV__ !== 'undefined' && __DEV__) rnInternalOnUnhandled(id, error)
       }
     })
     return () => rnPromise.disable()
   }
 }
 
-// this function is copied in from the promise module, since it's not exported and we can't reference it:
-// https://github.com/then/promise/blob/91b7b4cb6ad0cacc1c70560677458fe0aac2fa67/src/rejection-tracking.js#L101-L107
-function logError (id, error) {
-  console.warn('Possible Unhandled Promise Rejection (id: ' + id + '):')
-  var errStr = (error && (error.stack || error)) + ''
-  errStr.split('\n').forEach(function (line) {
-    console.warn('  ' + line)
-  })
+// This is a direct copy (with flow types removed) from RN internal code. In v0.64+ it is possible to reference, but in
+// older versions we can't access it so simply have to copy it.
+// https://github.com/facebook/react-native/blob/4409642811c787052e0baeb92e2679a96002c1e3/Libraries/Promise.js#L21-L46
+const rnInternalOnUnhandled = (id, rejection) => {
+  let message
+  let stack
+
+  const stringValue = Object.prototype.toString.call(rejection)
+  if (stringValue === '[object Error]') {
+    message = Error.prototype.toString.call(rejection)
+    const error = rejection
+    stack = error.stack
+  } else {
+    try {
+      message = require('pretty-format')(rejection)
+    } catch {
+      message =
+        typeof rejection === 'string'
+          ? rejection
+          : JSON.stringify(rejection)
+    }
+  }
+
+  const warning =
+    `Possible Unhandled Promise Rejection (id: ${id}):\n` +
+    `${message ?? ''}\n` +
+    (stack == null ? '' : stack)
+  console.warn(warning)
 }