child_process: treat already-aborted controller as aborting

If an AbortController passed to execfile() is already aborted, use the
same behavior as if the controller was aborted after calling execfile().
This mimics the behavior of fetch in the browser.

PR-URL: #36644
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>

lib/child_process.js

@@ -376,6 +376,8 @@ function execFile(file /* , args, options, callback */) {
   }
   if (options.signal) {
     if (options.signal.aborted) {
+      if (!ex)
+        ex = new AbortError();
       process.nextTick(() => kill());
     } else {
       const childController = new AbortController();

test/parallel/test-child-process-execfile.js

@@ -53,25 +53,19 @@ const execOpts = { encoding: 'utf8', shell: true };
   const ac = new AbortController();
   const { signal } = ac;
 
-  const firstCheck = common.mustCall((err) => {
-    assert.strictEqual(err.code, 'ABORT_ERR');
-    assert.strictEqual(err.name, 'AbortError');
-    assert.strictEqual(err.signal, undefined);
-  });
-
-  const secondCheck = common.mustCall((err) => {
-    assert.strictEqual(err.code, null);
-    assert.strictEqual(err.name, 'Error');
-    assert.strictEqual(err.signal, 'SIGTERM');
-  });
-
-  execFile(process.execPath, [echoFixture, 0], { signal }, (err) => {
-    firstCheck(err);
-    // Test that re-using the aborted signal results in immediate SIGTERM.
-    execFile(process.execPath, [echoFixture, 0], { signal }, secondCheck);
-  });
+  const test = () => {
+    const check = common.mustCall((err) => {
+      assert.strictEqual(err.code, 'ABORT_ERR');
+      assert.strictEqual(err.name, 'AbortError');
+      assert.strictEqual(err.signal, undefined);
+    });
+    execFile(process.execPath, [echoFixture, 0], { signal }, check);
+  };
 
+  test();
   ac.abort();
+  // Verify that it still works the same way now that the signal is aborted.
+  test();
 }
 
 {