Why am I getting an error regarding Bolts framework and FacebookSDK when I'm not even using Bolts?

1. Open the project in Xcode.
2. Go to where you extracted the FacebookSDK. If you're using Mac OSX, it should be available in Documents/FacebookSDK.
3. Grab the Bolts.framework file and drop into your Frameworks folder in Xcode for your project.

It should build now.

you need to add Bolts.framework to your project

As of 24th of April 2019, the Facebook SDK in Swift repo inside this commit:

Removed Bolts from Swift SDK

So you will have to add Bolts to your pod file. FYI if you're using Swift 5 you will need to use the Bolts in Objc because currently Bolts for Swift only support Swift 4.1.

For Swift 5 in your pod file:

pod 'Bolts'

To answer your question, from Bolts GitHub:

Bolts is a collection of low-level libraries designed to make developing mobile apps easier. Bolts was designed by Parse and Facebook for our own internal use

EDIT / UPDATE:

It looks like Bolts for Swift now support Swift 5.