transloadit: throw and warn when using the old Uppy Server URL (#1038)

Shows up in the informer and in the console when trying to upload a file
from a remote source. Kinda sucks that you have to actually do it, but
this is the easiest place to implement it…else we have to look at other
plugins' private options and hope that users are adding the plugins in
an order that makes that possible.

packages/@uppy/transloadit/src/index.js

@@ -17,6 +17,7 @@ function defaultGetAssemblyOptions (file, options) {
 const COMPANION = 'https://api2.transloadit.com/companion'
 // Regex used to check if a Companion address is run by Transloadit.
 const TL_COMPANION = /https?:\/\/api2(?:-\w+)?\.transloadit\.com\/companion/
+const TL_UPPY_SERVER = /https?:\/\/api2(?:-\w+)?\.transloadit\.com\/uppy-server/
 
 /**
  * Upload files to Transloadit using Tus.
@@ -103,6 +104,18 @@ module.exports = class Transloadit extends Plugin {
     // We only replace the hostname for Transloadit's companions, so that
     // people can also self-host them while still using Transloadit for encoding.
     let remote = file.remote
+    if (file.remote && TL_UPPY_SERVER.test(file.remote.serverUrl)) {
+      const err = new Error(
+        'The https://api2.transloadit.com/uppy-server endpoint was renamed to ' +
+        'https://api2.transloadit.com/companion, please update your `serverUrl` ' +
+        'options accordingly.')
+      // Explicitly log this error here because it is caught by the `createAssembly`
+      // Promise further along.
+      // That's fine, but createAssembly only shows the informer, we need something a
+      // little more noisy.
+      this.uppy.log(err)
+      throw err
+    }
     if (file.remote && TL_COMPANION.test(file.remote.serverUrl)) {
       let newHost = status.companion_url
         .replace(/\/$/, '')
@@ -681,3 +694,4 @@ module.exports = class Transloadit extends Plugin {
 }
 
 module.exports.COMPANION = COMPANION
+module.exports.UPPY_SERVER = COMPANION