fix(mixedModuleGraph): handle undefined id in getModulesByFile

[bluwy]

Description

Handle undefined id in getModulesByFile. I tested it manually with Astro to verify that it fixes its e2e tests, but I've not added test (withastro/astro#11979) 😬

[stackblitz]

Run & review this pull request in StackBlitz Codeflow.

[patak-dev]

I still don't understand why we have modules without an id 🤔
Let's merge this though to unblock testing other things in Astro.

[sapphi-red]

This seems to be the reason.

vite/packages/vite/src/node/server/moduleGraph.ts

Lines 388 to 391 in b513836

	// some deps, like a css file referenced via @import, don't have its own
	// url because they are inlined into the main css import. But they still
	// need to be represented in the module graph so that they can trigger
	// hmr in the importing css file.

[patak-dev]

Ah, that makes sense. I wonder if in this case we should also set an id for the module. We could set id and url to it, or add a prefix like \0fileOnlyEntry.

This code in that function doesn't seems right to me:

    const url = `${FS_PREFIX}${file}`
    for (const m of fileMappedModules) {
      if (m.url === url || m.id === file) {
        return m
      }
    }

If we first resolve a module that has file as its id, and then go through this code, we return that module and both are merged.
If we first go through this code, and then later on we resolve a module with the same file as id, we end up creating two modules. I think setting the id to be the file would avoid this.

[sapphi-red]

That's true. Adding a prefix feels more correct to me. The content of modules should be unique for each id and should set an id different from normal modules.

BTW if we have files like:

• main.js: contains import './foo.css'
• foo.css: contains @import './bar.css'
• bar.css

and a framework is going to inject link tags to avoid FOUC, they will want to only inject foo.css, otherwise there will be duplicate styles injected. How are they handling this in the current state? I guess it won't be a big problem though, it will just have duplicate styles.