@uppy/core: fix plugin detection

[aduh95]

Using instanceof is problematic as it won't detect plugins from different Uppy distributions. Whether we should support that use-case is certainly debatable – having more than one Uppy distribution is good indication that there's a bug in the build chain – but it seems useful to only produce a warning rather than failing hard.

[github-actions]

Diff output files

diff --git a/packages/@uppy/core/lib/UIPlugin.js b/packages/@uppy/core/lib/UIPlugin.js
index c640aa7..4d04353 100644
--- a/packages/@uppy/core/lib/UIPlugin.js
+++ b/packages/@uppy/core/lib/UIPlugin.js
@@ -40,8 +40,21 @@ class UIPlugin extends BasePlugin {
   }
   getTargetPlugin(target) {
     let targetPlugin;
-    if (typeof target === "object" && target instanceof UIPlugin) {
+    if (typeof (target == null ? void 0 : target.addTarget) === "function") {
       targetPlugin = target;
+      if (!(targetPlugin instanceof UIPlugin)) {
+        console.warn(
+          new Error(
+            "The provided plugin is not an instance of UIPlugin. This is an indication of a bug with the way Uppy is bundled.",
+            {
+              cause: {
+                targetPlugin,
+                UIPlugin,
+              },
+            },
+          ),
+        );
+      }
     } else if (typeof target === "function") {
       const Target = target;
       this.uppy.iteratePlugins(p => {

[Murderlon]

It's a bit weird but I don't know an alternative now