child_process: harden fork arguments validation

Ensure that the first argument `modulePath` of `fork` method
must be provided and be of type string.

PR-URL: #27039
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

lib/child_process.js

@@ -62,6 +62,7 @@ function stdioStringToArray(option) {
 }
 
 exports.fork = function fork(modulePath /* , args, options */) {
+  validateString(modulePath, 'modulePath');
 
   // Get options and args arguments.
   var execArgv;

test/parallel/test-child-process-fork-args.js

@@ -0,0 +1,105 @@
+'use strict';
+const common = require('../common');
+const fixtures = require('../common/fixtures');
+const assert = require('assert');
+const { fork } = require('child_process');
+
+// This test check the arguments of `fork` method
+// Refs: https://github.com/nodejs/node/issues/20749
+const expectedEnv = { foo: 'bar' };
+
+// Ensure that first argument `modulePath` must be provided
+// and be of type string
+{
+  const invalidModulePath = [
+    0,
+    true,
+    undefined,
+    null,
+    [],
+    {},
+    () => {},
+    Symbol('t')
+  ];
+  invalidModulePath.forEach((modulePath) => {
+    common.expectsError(() => fork(modulePath), {
+      code: 'ERR_INVALID_ARG_TYPE',
+      type: TypeError,
+      message: /^The "modulePath" argument must be of type string/
+    });
+  });
+
+  const cp = fork(fixtures.path('child-process-echo-options.js'));
+  cp.on(
+    'exit',
+    common.mustCall((code) => {
+      assert.strictEqual(code, 0);
+    })
+  );
+}
+
+// Ensure that the second argument of `fork`
+// and `fork` should parse options
+// correctly if args is undefined or null
+{
+  const invalidSecondArgs = [
+    0,
+    true,
+    () => {},
+    Symbol('t')
+  ];
+  invalidSecondArgs.forEach((arg) => {
+    common.expectsError(
+      () => {
+        fork(fixtures.path('child-process-echo-options.js'), arg);
+      },
+      {
+        code: 'ERR_INVALID_ARG_VALUE',
+        type: TypeError
+      }
+    );
+  });
+
+  const argsLists = [undefined, null, []];
+
+  argsLists.forEach((args) => {
+    const cp = fork(fixtures.path('child-process-echo-options.js'), args, {
+      env: Object.assign({}, process.env, expectedEnv)
+    });
+
+    cp.on(
+      'message',
+      common.mustCall(({ env }) => {
+        assert.strictEqual(env.foo, expectedEnv.foo);
+      })
+    );
+
+    cp.on(
+      'exit',
+      common.mustCall((code) => {
+        assert.strictEqual(code, 0);
+      })
+    );
+  });
+}
+
+// Ensure that the third argument should be type of object if provided
+{
+  const invalidThirdArgs = [
+    0,
+    true,
+    () => {},
+    Symbol('t')
+  ];
+  invalidThirdArgs.forEach((arg) => {
+    common.expectsError(
+      () => {
+        fork(fixtures.path('child-process-echo-options.js'), [], arg);
+      },
+      {
+        code: 'ERR_INVALID_ARG_VALUE',
+        type: TypeError
+      }
+    );
+  });
+}