Gère le cas où le login est déjà pris à l'inscription

src/Silex/DI/DI.php

@@ -66,7 +66,8 @@ class DI
     private function getPDO(): PDO
     {
         if ($this->pdo === null) {
-            return new PDO(sprintf('mysql:host=%s;dbname=%s', DB_HOST, DB_DATABASE), DB_USER, DB_PASSWORD);
+            $this->pdo = new PDO(sprintf('mysql:host=%s;dbname=%s', DB_HOST, DB_DATABASE), DB_USER, DB_PASSWORD);
+            $this->pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
         }
         return $this->pdo;
     }

src/Silex/Gateway/UniqueViolation.php

@@ -0,0 +1,15 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Silex\Gateway;
+
+use PDOException;
+
+final class UniqueViolation
+{
+    public static function isUniqueViolation(PDOException $ex): bool
+    {
+        return $ex->errorInfo[1] === 1062; // Mysql
+    }
+}

src/Silex/Gateway/UserGateway.php

@@ -5,6 +5,7 @@ declare(strict_types=1);
 namespace Silex\Gateway;
 
 use PDO;
+use PDOException;
 use Silex\Model\User;
 
 class UserGateway
@@ -37,7 +38,14 @@ class UserGateway
     public function insert(User $user): bool
     {
         $req = $this->pdo->prepare('INSERT INTO registered_user (login, password, role) VALUES (:login, :password, :role);');
+        try {
             $req->execute(['login' => $user->getLogin(), 'password' => $user->getPasswordHash(), 'role' => $user->getRole()]);
+        } catch (PDOException $ex) {
+            if (UniqueViolation::isUniqueViolation($ex)) {
+                return false;
+            }
+            throw $ex;
+        }
         $user->setId(intval($this->pdo->lastInsertId()));
         return true;
     }

tables.sql

@@ -1,6 +1,6 @@
 CREATE TABLE registered_user (
     id_user SERIAL PRIMARY KEY,
-    login VARCHAR(32) NOT NULL,
+    login VARCHAR(32) NOT NULL UNIQUE,
     password CHAR(72) NOT NULL, -- BCrypt
     role INT NOT NULL DEFAULT 0
 );