repl: do not run --eval code if there is none

`getOptionValue('--eval')` always returns a string, so it is never
loose-equal to `null`. Running eval makes some modifications to the
global object, including setting `module` to a different value, which
we want to avoid if possible.

Refs: #27278
PR-URL: #27587
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: John-David Dalton <john.david.dalton@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>

lib/internal/main/repl.js

@@ -46,10 +46,9 @@ cliRepl.createInternalRepl(process.env, (err, repl) => {
 
 // If user passed '-e' or '--eval' along with `-i` or `--interactive`,
 // evaluate the code in the current context.
-const source = getOptionValue('--eval');
-if (source != null) {
+if (getOptionValue('[has_eval_string]')) {
   evalScript('[eval]',
-             source,
+             getOptionValue('--eval'),
              getOptionValue('--inspect-brk'),
              getOptionValue('--print'));
 }

test/parallel/test-repl-cli-eval.js

@@ -0,0 +1,22 @@
+'use strict';
+const common = require('../common');
+const child_process = require('child_process');
+const assert = require('assert');
+
+// Regression test for https://github.com/nodejs/node/issues/27575:
+// module.id === '<repl>' in the REPL.
+
+for (const extraFlags of [[], ['-e', '42']]) {
+  const flags = ['--interactive', ...extraFlags];
+  const proc = child_process.spawn(process.execPath, flags, {
+    stdio: ['pipe', 'pipe', 'inherit']
+  });
+  proc.stdin.write('module.id\n.exit\n');
+
+  let stdout = '';
+  proc.stdout.setEncoding('utf8');
+  proc.stdout.on('data', (chunk) => stdout += chunk);
+  proc.stdout.on('end', common.mustCall(() => {
+    assert(stdout.includes('<repl>'), `stdout: ${stdout}`);
+  }));
+}