src,test: fix config file parsing for flags defaulted to true

PR-URL: https://github.com/nodejs/node/pull/59110
Reviewed-By: Pietro Marchini <pietro.marchini94@gmail.com>
Reviewed-By: Marco Ippolito <marcoippolito54@gmail.com>
Reviewed-By: Jacob Smith <jacob@frende.me>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>

src/node_config_file.cc

@@ -55,6 +55,10 @@ ParseResult ConfigReader::ProcessOptionValue(
       if (result) {
         // If the value is true, we need to set the flag
         output->push_back(option_name);
+      } else {
+        // Ensure negation is made putting the "--no-" prefix
+        output->push_back("--no-" +
+                          option_name.substr(2, option_name.size() - 2));
       }
 
       break;

test/fixtures/rc/warnings-false.json

@@ -0,0 +1,5 @@
+{
+  "nodeOptions": {
+    "warnings": false
+  }
+}

test/parallel/test-config-file.js

@@ -60,6 +60,17 @@ test('should parse boolean flag', async () => {
   strictEqual(result.code, 0);
 });
 
+test('should parse boolean flag defaulted to true', async () => {
+  const result = await spawnPromisified(process.execPath, [
+    '--experimental-config-file',
+    fixtures.path('rc/warnings-false.json'),
+    '-p', 'process.emitWarning("A warning")',
+  ]);
+  strictEqual(result.stderr, '');
+  strictEqual(result.stdout, 'undefined\n');
+  strictEqual(result.code, 0);
+});
+
 test('should throw an error when a flag is declared twice', async () => {
   const result = await spawnPromisified(process.execPath, [
     '--no-warnings',