Add prompt suggesting using --dev when require command is used with dev packages

doc/04-schema.md

@@ -119,6 +119,10 @@ Examples:
 - redis
 - templating
 
+> **Note**: Some special keywords trigger `composer require` without the
+> `--dev` option to prompt users if they would like to add these packages to
+> `require-dev` instead of `require`. These are: `dev`, `testing`, `static analysis`.
+
 Optional.
 
 ### homepage

src/Composer/Command/RequireCommand.php

@@ -13,7 +13,10 @@
 namespace Composer\Command;
 
 use Composer\DependencyResolver\Request;
+use Composer\Package\CompletePackageInterface;
+use Composer\Package\PackageInterface;
 use Composer\Util\Filesystem;
+use Composer\Util\PackageSorter;
 use Seld\Signal\SignalHandler;
 use Symfony\Component\Console\Input\InputInterface;
 use Composer\Console\Input\InputArgument;
@@ -218,9 +221,36 @@ protected function execute(InputInterface $input, OutputInterface $output)
             throw $e;
         }
 
+        $requirements = $this->formatRequirements($requirements);
+
+        if (!$input->getOption('dev') && $io->isInteractive()) {
+            $devPackages = [];
+            $devTags = ['dev', 'testing', 'static analysis'];
+            $currentRequiresByKey = $this->getPackagesByRequireKey();
+            foreach ($requirements as $name => $version) {
+                // skip packages which are already in the composer.json as those have already been decided
+                if (isset($currentRequiresByKey[$name])) {
+                    continue;
+                }
+
+                $pkg = PackageSorter::getMostCurrentVersion($this->getRepos()->findPackages($name));
+                if ($pkg instanceof CompletePackageInterface && count(array_intersect($devTags, array_map('strtolower', $pkg->getKeywords()))) > 0) {
+                    $devPackages[] = $name;
+                }
+            }
+
+            if (count($devPackages) === count($requirements)) {
+                $plural = count($requirements) > 1 ? 's' : '';
+                $plural2 = count($requirements) > 1 ? 'are' : 'is';
+                $io->warning('The package'.$plural.' you required '.$plural2.' recommended to be placed in require-dev but you did not use --dev.');
+                if ($io->askConfirmation('<info>Do you want to re-run the command with --dev?</> [<comment>yes</>]? ')) {
+                    $input->setOption('dev', true);
+                }
+            }
+        }
+
         $requireKey = $input->getOption('dev') ? 'require-dev' : 'require';
         $removeKey = $input->getOption('dev') ? 'require' : 'require-dev';
-        $requirements = $this->formatRequirements($requirements);
 
         // validate requirements format
         $versionParser = new VersionParser();
@@ -254,6 +284,7 @@ protected function execute(InputInterface $input, OutputInterface $output)
                         return 0;
                     }
 
+                    $input->setOption('dev', true);
                     list($requireKey, $removeKey) = array($removeKey, $requireKey);
                 }
             }

src/Composer/Util/PackageSorter.php

@@ -17,6 +17,34 @@
 
 class PackageSorter
 {
+    /**
+     * Returns the most recent version of a set of packages
+     *
+     * This is ideally the default branch version, or failing that it will return the package with the highest version
+     *
+     * @template T of PackageInterface
+     * @param array<T> $packages
+     * @return ($packages is non-empty-array<T> ? T : T|null)
+     */
+    public static function getMostCurrentVersion(array $packages): ?PackageInterface
+    {
+        return array_reduce($packages, function ($carry, $pkg) {
+            if ($carry === null) {
+                return $pkg;
+            }
+
+            if ($pkg->isDefaultBranch()) {
+                return $pkg;
+            }
+
+            if (!$carry->isDefaultBranch() && version_compare($carry->getVersion(), $pkg->getVersion(), '<')) {
+                return $pkg;
+            }
+
+            return $carry;
+        });
+    }
+
     /**
      * Sorts packages by name
      *