lib noderawfs now requires FS.init()

[walkingeyerobot]

Previously I was able to call FS.chdir() when using noderawfs without first calling FS.init(), but now I have to call FS.init() first. I think that just means the docs need to be updated here because FS.init() does more than just set up standard I/O devices in this case: https://emscripten.org/docs/api_reference/Filesystem-API.html?highlight=filesystem#setting-up-standard-i-o-devices

[sbc100]

IIUC FS.init() should automatically be called when the module loads. Did that somehow change maybe? Can you share more details and perhaps we can construct a test case.

[walkingeyerobot]

It's entirely possible (even likely) that I'm holding it wrong. I'm running some JS before the emscripten JS that looks approximately like this:

var Module = typeof Module !== 'undefined' ? Module : {
  arguments: [],
  preRun: [function() {
    ENV = typeof ENV !== "undefined" ? ENV : {};
    ENV.FOO = 'const'; // lots of lines like this
    FS.chdir('/usr/local/bar');
  }]
};

This was working fine under 3.1.63 (and for a loooong time before that) and has broken under 3.1.65. If I run FS.init(); before I call FS.chdir it works as expected.

I'm not going through --pre-js; maybe that's the problem?

[sbc100]

That looks like something that we should continue to support. I'll see if I can repro and fix.

[sbc100]

What error message do you see when you don't call FS.init(). Can't seem to replicate this using a trivial example:

$ cat test.js 
Module.preRun = [function() {
    FS.mkdir('/foo');
    FS.chdir('/foo');
}];
$ emcc --pre-js test.js ~/test/hello.c -sFORCE_FILESYSTEM
$ node ./a.out.js 
Hello, world!

[kleisauke]

This looks like a oversight on my part. Commit c614fa5 introduced the regression, which was later reverted by commit 659f01d, while keeping the filesystem wrapping in FS.init() to minimize the diff.

I just opened PR #22559 for this.

[walkingeyerobot]

Without the FS.init() I get a very cryptic error message:

exception caught:  [<generic error, no stack>] {
  name: 'ErrnoError',
  errno: 44,
  code: 'ENOENT'
}

I was able to trace that to here: https://github.com/emscripten-core/emscripten/blob/main/src/library_memfs.js#L176

[walkingeyerobot]

I'll also add that I'm on node v18.17.0 and I'm unable to change the version of node I'm on.

[sbc100]

I think #22559 will fix this issue.