Enhancement: Add --dry-run option

README.md

@@ -36,6 +36,7 @@ The `NormalizeCommand` provided by the `NormalizePlugin` within this package wil
 
 ### Options
 
+* `--dry-run`: Show the results of normalizing, but do not modify any files
 * `--indent-size`: Indent size (an integer greater than 0); should be used with the `--indent-style` option
 * `--indent-style`: Indent style (one of "space", "tab"); should be used with the `--indent-size` option
 * `--no-update-lock`: Do not update lock file if it exists

composer.json

@@ -19,7 +19,8 @@
   "require": {
     "php": "^7.1",
     "composer-plugin-api": "^1.1.0",
-    "localheinz/json-normalizer": "0.4.0"
+    "localheinz/json-normalizer": "0.4.0",
+    "sebastian/diff": "^2.0.1"
   },
   "require-dev": {
     "composer/composer": "^1.1.0",

src/Command/NormalizeCommand.php

@@ -16,6 +16,7 @@
 use Composer\Command;
 use Composer\Factory;
 use Localheinz\Json\Normalizer;
+use SebastianBergmann\Diff;
 use Symfony\Component\Console;
 
 final class NormalizeCommand extends Command\BaseCommand
@@ -43,22 +44,35 @@ final class NormalizeCommand extends Command\BaseCommand
      */
     private $formatter;
 
+    /**
+     * @var Diff\Differ
+     */
+    private $differ;
+
     public function __construct(
         Normalizer\NormalizerInterface $normalizer,
         Normalizer\Format\SnifferInterface $sniffer = null,
-        Normalizer\Format\FormatterInterface $formatter = null
+        Normalizer\Format\FormatterInterface $formatter = null,
+        Diff\Differ $differ = null
     ) {
         parent::__construct('normalize');
 
         $this->normalizer = $normalizer;
         $this->sniffer = $sniffer ?: new Normalizer\Format\Sniffer();
         $this->formatter = $formatter ?: new Normalizer\Format\Formatter();
+        $this->differ = $differ ?: new Diff\Differ();
     }
 
     protected function configure(): void
     {
         $this->setDescription('Normalizes composer.json according to its JSON schema (https://getcomposer.org/schema.json).');
         $this->setDefinition([
+            new Console\Input\InputOption(
+                'dry-run',
+                null,
+                Console\Input\InputOption::VALUE_NONE,
+                'Show the results of normalizing, but do not modify any files'
+            ),
             new Console\Input\InputOption(
                 'indent-size',
                 null,
@@ -87,6 +101,8 @@ protected function execute(Console\Input\InputInterface $input, Console\Output\O
     {
         $io = $this->getIO();
 
+        $dryRun = $input->getOption('dry-run');
+
         try {
             $indent = $this->indentFrom($input);
         } catch (\RuntimeException $exception) {
@@ -157,6 +173,30 @@ protected function execute(Console\Input\InputInterface $input, Console\Output\O
             return 0;
         }
 
+        if ($dryRun) {
+            $io->writeError(\sprintf(
+                '<error>%s is not normalized.</error>',
+                $composerFile
+            ));
+
+            $io->write([
+                '',
+                '<fg=green>--- original </>',
+                '<fg=red>+++ normalized </>',
+                '',
+                '<fg=yellow>---------- begin diff ----------</>',
+            ]);
+
+            $io->write($this->diff(
+                $json,
+                $formatted
+            ));
+
+            $io->write('<fg=yellow>----------- end diff -----------</>');
+
+            return 1;
+        }
+
         \file_put_contents($composerFile, $formatted);
 
         $io->write(\sprintf(
@@ -256,6 +296,37 @@ private function composerFile(): string
         return $composerFile;
     }
 
+    /**
+     * @param string $before
+     * @param string $after
+     *
+     * @return string[]
+     */
+    private function diff(string $before, string $after): array
+    {
+        $diff = $this->differ->diffToArray(
+            $before,
+            $after
+        );
+
+        return \array_map(function (array $element) {
+            static $templates = [
+                0 => ' %s',
+                1 => '<fg=green>+%s</>',
+                2 => '<fg=red>-%s</>',
+            ];
+
+            [$token, $status] = $element;
+
+            $template = $templates[$status];
+
+            return \sprintf(
+                $template,
+                $token
+            );
+        }, $diff);
+    }
+
     /**
      * @see https://getcomposer.org/doc/03-cli.md#validate
      *