Add command that shows merge plan path

src/Command/ConfigCommand.php

@@ -0,0 +1,38 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Yiisoft\Config\Command;
+
+use Composer\Command\BaseCommand;
+use Symfony\Component\Console\Input\InputInterface;
+use Symfony\Component\Console\Output\OutputInterface;
+use Yiisoft\Config\Composer\ProcessHelper;
+
+/**
+ * `ConfigCommand`
+ */
+final class ConfigCommand extends BaseCommand
+{
+    protected function configure(): void
+    {
+        $this
+            ->setName('yii-config-merge-plan');
+    }
+
+    protected function execute(InputInterface $input, OutputInterface $output): int
+    {
+        /**
+         * @psalm-suppress PossiblyNullArgument
+         * @psalm-suppress DeprecatedMethod
+         */
+        $helper = new ProcessHelper($this->getComposer());
+        $output->write(
+            $helper->getPaths()->absolute(
+                $helper->getMergePlanFile()
+            )
+        );
+
+        return 0;
+    }
+}

src/Command/ConfigCommandProvider.php

@@ -16,6 +16,7 @@ public function getCommands(): array
         return [
             new CopyCommand(),
             new RebuildCommand(),
+            new ConfigCommand(),
         ];
     }
 }