Make wasm plugin work with service workers

[vedantroy]

The code generated by @rollup/plugin-wasm breaks when executed in a
service worker because window is undefined.

Rollup Plugin Name: wasm

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• [] no

This is a draft PR because I'm not sure how to write a test that runs code inside a service worker. Once I figure that out, I will add a test and update the above checkbox.

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

List any relevant issue numbers: #333

Description

This PR adds a check for whether window is undefined. This PR makes the loader function use globalThis instead of window. Prior to this, @rollup/plugin-wasm would break when the resulting generated code was run in a service worker, because it assumed window was defined.

[shellscape]

Thanks for taking this on. We'll leave this open and pending until you give the go-ahead to review.

[vedantroy]

@shellscape I added a test and refactored test.js because I needed to pass the code generated by rollup into a Worker instead of testBundle.

Note: The test is a bit fragile because I have to fake the browser environment (atob does not exist on globalThis in node, so I polyfilled it, and I undefined process to force the wasm loader to go into the browser section). However, I think it's the most reasonable test that is possible.

The test can only run on node versions where worker_threads is available (node > 11.7.0), so I skip the test on earlier versions of node.

Edit: I see the CI is failing for Node version 10 because worker_threads is not a module. I can fix this by installing the threads library (https://www.npmjs.com/package/threads) as a dev dependency, so the tests can pass on Node 10. But confirming this ok, before I do it because I don't know if adding a dependency (even if it is a dev dependency) is a good idea.

An alternative is to just merge the PR without a test? because the change is very trivial (replacing window with globalThis).

Edit 2: Seems like the threads package is not a drop in replacement for worker_threads in Node, so this will be more complicated than I thought.

[shellscape]

Thanks for the PR!

@ColinEberhardt and @jamen would you two be willing to take a look at this one?

[jamen]

The worker test does seem a bit hacky, but I don't have a better idea, so its probably fine. The change affecting the other tests is functionally the same, so that's fine.

It should probably be added in a major version because there is a gap of support between WebAssembly and globalThis according to caniuse (1, 2).

Looks okay to me. 👍

[vedantroy]

@jamen The gap of support seems to show that WebAssembly is less supported than globalThis in all cases (except for Opera Mobile, which supports wasm but not globalThis). However, if this is an issue, I can add a check so it tries using window before globalThis.

[jamen]

What I mean is the browser versions. WebAssembly came first and globalThis came later, so there are versions where WebAssembly exists but globalThis doesn't. I believe that is a breaking change, because the build would be supported in a more limited range of versions than WebAssembly itself.

I don't think it needs changed, but it should be in a major version so it wouldn't surprise existing builds. I haven't been very active in web lately though, so someone else can make that call. But also, a build concerned about this should be using something like @babel/preset-env anyways.

[shellscape]

Thanks everyone!