Bug: Weird Vite chunk map sources

[IamFastre]

Describe the bug
I keep getting this annoying error message in my dev console:

Not found: /node_modules/@microsoft/fetch-event-source/src/parse.ts
Not found: /node_modules/@microsoft/fetch-event-source/src/fetch.ts

I did some investigating and found that this chunk map is generated

// node_modules/.vite/deps/chunk-6H7Z5HH6.js.map
{
  "version": 3,
  "sources": ["../../@microsoft/fetch-event-source/src/parse.ts", "../../@microsoft/fetch-event-source/src/fetch.ts"],
  "sourcesContent": [null, null],
  "mappings":  /* long string */,
  "names": ["_a"]
}

which doesn't exist, this causes my app to try to reoptimize the dependencies, so some unnecessary server restarts.

To Reproduce

1. Use Vite with Svelte 5?
2. Open the dev build site and volià

Expected behavior
Not to send those messages or generate this incorrect chunk

Desktop (please complete the following information):

• OS: Windows 11
• Browser: Chrome
• Version: latest
• Node: 22

Additional context
I know the issue might just be from the @microsoft/fetch-event-source package, and I made an issue there, but the project seems to be abandoned

[IamFastre]

maybe it's better to abandon @microsoft/fetch-event-source for something else?

[razshare]

Hello @IamFastre

first of all thanks for the issue.

maybe it's better to abandon @microsoft/fetch-event-source for something else?

I actually agree with this, regardless if @microsoft/fetch-event-source works fine or not.

The reason it's being used at the moment is so that we can provide custom headers for the request, which is useful for authantication/authorization.

I'm currently a bit more focused on a different project, but I'll try get back on this next week.

In the meantime, may I ask if this is also causing issues outside of dev mode? For example what happens if you build for production with source maps enabled?

[IamFastre]

Good evening!
So, in dev mode that's how the source map looks on Edge:

with it thinking it's in @microsoft/fetch-event-source/src/{file-name}.ts
but weirdly enough in preview it's normal:

and of course the same with running the node http server with node ./build/index.js

the source maps causing the problem in the @microsoft/fetch-event-source package seem to be:

• node_modules/@microsoft/fetch-event-source/lib/esm/index.js.map (doesn't even get chunked)
• node_modules/@microsoft/fetch-event-source/lib/esm/fetch.js.map
• node_modules/@microsoft/fetch-event-source/lib/esm/parse.js.map

So as it seems the problems is entirely from @microsoft/fetch-event-source and its building process, but apparently the project is abandoned by MS and Azure.

I tried patching it with bun patch in sveltekit-sse itself by adding the src/* from the original code of @microsoft/fetch-event-source and it did silence the error thing and show the correct sources, but I'm no expert with bun and bun seems to refuse to make new directories when patching for some reason, giving me this error

bun patch-commit v1.2.16 (631e6748)
error: failed applying patch file: ENOENT: No such file or directory (open())
error: failed to apply patchfile (patches/@microsoft%2Ffetch-event-source@2.0.1.patch)

while editing files seemed to work fine, and patch-package would work but it's npm only

[razshare]

Hello @IamFastre ,
I'm glad to say that I've managed to drop the @microsoft/fetch-event-source dependency completely by using a custom implementation of a fetchEventSource.

The current playwright tests all pass successfully.

I'll be writing some more playwright tests this week in order to make sure the new implementation works as intended.

It goes without saying that there are no api changes in userland.

These changes are not released nor merged into main yet, they're available in https://github.com/razshare/sveltekit-sse/tree/fetchEventSource .

I'll let you know when the new release is available.

[IamFastre]

Thanks so much for the efforts! and take your time, it's not that important or urgent.

[razshare]

Hello @IamFastre , I've just released v0.14.1 with the changes I mentioned above.

Please update your version and let me know if this fixes your issue.

[IamFastre]

Thank you so much!