Fix ENVIRONMENT_IS_WORKER detection on Deno

[kleisauke]

importScripts() is always undefined on Deno.

[kleisauke]

Test case:

Before:

$ cat > test.c << EOF
#include <assert.h>
#include <pthread.h>
#include <stdio.h>

#include <emscripten/em_asm.h>

void* worker_thread(void *arg) {
  int is_worker = EM_ASM_INT(return ENVIRONMENT_IS_WORKER);
  printf("ENVIRONMENT_IS_WORKER: %d\n", is_worker);
  return NULL;
}

int main() {
  int is_worker = EM_ASM_INT(return ENVIRONMENT_IS_WORKER);
  printf("ENVIRONMENT_IS_WORKER: %d\n", is_worker);

  pthread_t thread;
  pthread_create(&thread, NULL, worker_thread, NULL);
  pthread_join(thread, NULL);

  return 0;
}
EOF
$ emcc test.c -o test.js -sASSERTIONS=0 -pthread -sEXIT_RUNTIME
$ node test.js
ENVIRONMENT_IS_WORKER: 0
ENVIRONMENT_IS_WORKER: 1
$ emcc test.c -o test.mjs -sENVIRONMENT=web,worker -sASSERTIONS=0 -pthread
$ echo "import Module from './test.mjs';await Module();Deno.exit()" | deno run --allow-read -
ENVIRONMENT_IS_WORKER: 0 [repeated x times until OOM]

After:

$ emcc test.c -o test.mjs -sENVIRONMENT=web,worker -sASSERTIONS=0 -pthread
$ echo "import Module from './test.mjs';await Module();Deno.exit()" | deno run --allow-read -
ENVIRONMENT_IS_WORKER: 0
ENVIRONMENT_IS_WORKER: 1

[kripken]

Looks reasonable to me. The downside is maybe a few more bytes in size, but I don't see a way around that, and it mostly affects pthreads builds (which are larger anyhow).

other.test_no_pthread on CI will need to be updated a little, it looks like (it greps for Worker, which this PR adds; can first replace WorkerGlobalScope with another string, if there isn't anything nicer).

[sbc100]

I'm a little confused because you say that deno never defines importScripts, but from the looks of this code it seems that node doesn't define it either. Isn't the point of this line to inject it?

[kleisauke]

Ah, you're right. Node.js doesn't define importScripts either.

const { Worker, isMainThread } = require('node:worker_threads');

if (isMainThread) {
  // This re-loads the current file inside a Worker instance.
  new Worker(__filename);
} else {
  console.log(typeof importScripts);  // Prints 'undefined'.
}

Commit 4bab494 removes this altogether, since ENVIRONMENT_IS_WORKER no longer depends on this dummy symbol on Node.js:

emscripten/src/shell.js

Line 144 in 9e618aa

ENVIRONMENT_IS_WORKER = !worker_threads.isMainThread;

(I can separate this change into its own PR if needed)

[kleisauke]

Note that ENVIRONMENT_IS_NODE is false on Deno. IIUC, Deno tends to favor standard Web Platform APIs over proprietary ones and wasn't originally designed to be a drop-in replacement for Node.js.

[kripken]

Deno does have a Node.js compatibility layer these days (they started to compromise on that at some point, though they did start with "pure Web APIs" IIRC). I wonder if maybe we can make IS_NODE also accept deno, for simplicity? Separate from this PR of course. (And if it isn't trivial, then #12203 is probably the best long-term plan instead.)

This PR itself lgtm as is. Unless @sbc100 you had more thoughts?