Report errors encountered during bootPlaygroundRemote()

[adamziel]

Aims to improve the UX at #564 by bubbling up errors encountered when initializing workers.

This PR is meant to display an error message whenever there's a problem downloading any of the assets required to run the Playground including:

• .wasm files
• .data files
• Dynamic JavaScript imports
• Web worker
• Service worker

Testing instructions

1. Run npm run build
2. Run nx preview playground-website
3. Delete one of the files mentioned above in the build directory (build/packages/playground-website)
4. Confirm the error message was displayed

cc @dmsnell @ellatrix

[dmsnell]

before we have been running these and moving on possibly before they finish, but now with Promise.all we are pausing until they all finish. is that intentional?

also, we are using Promise.all so if a single data dependency throws an error the entire thing collapses.

• do we want to use Promise.allSettled so we can report failures for specific dependencies?
• if not, do we want to report the failure of any data dependency? because we're not wrapping this in a try/catch or adding any catch handler to any of the promises.

[adamziel]

Before we've waited for data dependencies, too, in one of the next lines: await depsReady;. That line is still there, in this PR, but maybe we don't need it anymore.

do we want to use Promise.allSettled so we can report failures for specific dependencies?

We could, but that would amount to the same outcome – display a loading error. Or would you like to do something more granular with that information?

do we want to report the failure of any data dependency?

That was my intention – try to download and start PHP and, if anything at all fails, reject the promise.

[adamziel]

No, we still need await depsReady; because it's resolved after the data dependencies have been both loaded and processed

[dmsnell]

We could, but that would amount to the same outcome – display a loading error. Or would you like to do something more granular with that information?

the point was that depsReady is all or nothing and .allSettled can tell us which dependencies failed. so if our goal is to expose more errors it could be beneficial to say something like "dependency {name} from {URL} failed to download" and be able to do that for each one that fails.

[adamziel]

Ah, I see what you mean! The information about the URL is included in the error message thrown by the Emscripten module. The ability to display multiple errors would still be nice, we’d just need to handle an array of error messages up the call stack.

Worth noting: data dependencies are produced by file_packager.py and we only load a single data dependency now: wp.data.

[adamziel]

I'll go ahead and merge to improve the "blank screen" loading experience. If we'll need more granular error info from Promise.allSettled() we can add it eventually.