Bug with bindings across compilation units

[hgiesel]

Describe the bug

Following scenario: we provide a base app (App.svelte), and some components for users to use (Component.svelte).

The users are supposed to provide their own add-on components (AddOn.svelte), which can use our components, and then add them to the base app through an interface app.addComponent(myaddon). The add-ons are then inserted using <svelte:element bind:this={myaddon} />

When using those provided components inside the add-on, we can set properties, but we cannot bind to them.

Reproduction

https://github.com/hgiesel/svelte-bug-example

Logs

No response

System Info

System:
    OS: macOS 11.2.3
    CPU: (8) x64 Intel(R) Core(TM) i7-1060NG7 CPU @ 1.20GHz
    Memory: 423.93 MB / 8.00 GB
    Shell: 5.1.4 - /usr/local/bin/bash
  Binaries:
    Node: 16.0.0 - /usr/local/bin/node
    Yarn: 1.22.5 - ~/.yarn/bin/yarn
    npm: 7.10.0 - /usr/local/bin/npm
  Browsers:
    Chrome: 91.0.4472.114
    Firefox: 89.0.2
    Safari: 14.0.3
  npmPackages:
    svelte: ^3.38.3 => 3.38.3

Severity

blocking all usage of svelte

[hgiesel]

I could hack it to work by changing:

var binding_callbacks = [];

from here to be

globalThis.binding_callbacks = globalThis.binding_callbacks || [];

That's obviously not the way to go, but it seems to me, that it's not just a bug, but that Svelte does not support combining multiple compilation outputs together. Is this out of scope for Svelte? I assume that in order for this to work, binding_callbacks, render_callbacks, etc. would have to be able to be passed into Svelte components, and also exported on demand so that it can be referenced by other components.

[hgiesel]

Could I get a feedback for this issue. It would really help me plan for the future.

[dae]

So, the problem here turned out to be bundling multiple copies of svelte/internal, as each copy retains its own state. We were able to work around the issue by exporting the copy bundled with the base code as a global. We exclude svelte from the add-on bundle, and map the call to require("svelte/internal") at runtime to the base code's copy of svelte/internal.

[Conduitry]

I'm going to close this. Bundling multiple copies of the internals causes a number of issues.