feature: added --drop-if-exists option to postgresql migrator

documentation/components/bridges/symfony-postgresql-bundle.md

@@ -143,8 +143,15 @@ flow_postgresql:
     rollback_file_name: "rollback.php"             # Name of the rollback file in each version directory
     all_or_nothing: false                          # Wrap all migrations in a single transaction
     generate_rollback: true                        # Generate rollback files automatically
+    drop_if_exists: false                          # Emit IF EXISTS on diff-generated DROP statements
 ```
 
+#### `drop_if_exists`
+
+Set `drop_if_exists: true` to render every diff-generated `DROP` with `IF EXISTS` — useful for convergence migrations
+that run against both fresh and legacy databases. Default `false`, so a missing object fails loudly (drift detection).
+Override for a single run with the [`--drop-if-exists`](#generating-migrations-from-schema-diff) flag.
+
 ### Catalog Providers
 
 Catalog providers define the target database schema. When you run `flow:migrations:diff`, the bundle compares
@@ -316,6 +323,7 @@ These commands are available when `migrations.enabled: true` for at least one co
 | `--up` / `--down`     | Migration direction (execute)                         |
 | `--allow-empty-diff`  | Don't fail when no changes detected (diff)            |
 | `--from-empty-schema` | Generate as if the database were empty (diff)         |
+| `--drop-if-exists`    | Emit `IF EXISTS` on generated DROP statements (diff)  |
 
 ## Migration Workflow
 
@@ -349,6 +357,13 @@ with the catalog, and `rollback.php` with the reverse operations (if `generate_r
 
 Use `--from-empty-schema` to generate a migration as if the database were empty (useful for initial setup).
 
+Use `--drop-if-exists` to emit `IF EXISTS` on every generated `DROP` for this run (a per-run override of the
+[`drop_if_exists`](#drop_if_exists) config key):
+
+```bash
+php bin/console flow:migrations:diff --drop-if-exists
+```
+
 ### Generating Blank Migrations
 
 Create an empty migration for manual SQL (data migrations, custom operations):

documentation/components/libs/postgresql.md

@@ -33,6 +33,7 @@ execute it with the Client, and map results to objects.
 | Add pagination to existing queries | [Query Modification](#query-modification)                                          | `ext-pg_query`              |
 | Analyze query performance          | [Query Plan Analysis](/documentation/components/libs/postgresql/client-explain.md) | `ext-pgsql`, `ext-pg_query` |
 | Traverse or modify AST directly    | [Advanced Features](#advanced-features)                                            | `ext-pg_query`              |
+| Generate SQL from schema diffs     | [Schema Diff](#schema-diff)                                                        | `ext-pg_query`              |
 
 ## Requirements
 
@@ -687,6 +688,42 @@ foreach ($query->raw()->getStmts() as $stmt) {
 
 ---
 
+## Schema Diff
+
+Compare two catalogs and generate the SQL that turns the source into the target.
+
+```php
+<?php
+
+use Flow\PostgreSql\Schema\Catalog;
+
+use function Flow\PostgreSql\DSL\{catalog_comparator, schema, schema_column_integer, schema_table};
+
+$current = new Catalog([schema('public', tables: [schema_table('users', [schema_column_integer('id', false)])])]);
+$target = new Catalog([schema('public')]); // users removed
+
+foreach (catalog_comparator()->compare($current, $target)->generate() as $sql) {
+    echo $sql->toSql() . "\n"; // DROP TABLE public.users CASCADE
+}
+```
+
+### `dropIfExists`
+
+By default, generated `DROP` statements have no `IF EXISTS`, so a missing object fails loudly (drift detection).
+Set `dropIfExists: true` to render every diff-generated drop with `IF EXISTS` — useful for convergence migrations
+that must run against both fresh and legacy databases:
+
+```php
+// On the comparator (applies to every compare):
+catalog_comparator(dropIfExists: true)->compare($current, $target);
+
+// Or per call (overrides the comparator's default):
+catalog_comparator()->compare($current, $target, dropIfExists: true);
+// -> DROP TABLE IF EXISTS public.users CASCADE
+```
+
+---
+
 ## Reference
 
 ### Exception Handling

src/bridge/symfony/postgresql-bundle/src/Flow/Bridge/Symfony/PostgreSqlBundle/Command/DiffCommand.php

@@ -41,7 +41,13 @@ protected function configure(): void
             ->addOption('connection', 'c', InputOption::VALUE_OPTIONAL, 'The connection to use', null)
             ->addArgument('name', InputArgument::OPTIONAL, 'The name of the migration (e.g. \'add_categories\')')
             ->addOption('allow-empty-diff', null, InputOption::VALUE_NONE, 'Do not throw when no changes are detected')
-            ->addOption('from-empty-schema', null, InputOption::VALUE_NONE, 'Generate as if the database were empty');
+            ->addOption('from-empty-schema', null, InputOption::VALUE_NONE, 'Generate as if the database were empty')
+            ->addOption(
+                'drop-if-exists',
+                null,
+                InputOption::VALUE_NONE,
+                'Emit IF EXISTS on generated DROP statements (overrides the migrations.drop_if_exists config for this run)',
+            );
     }
 
     protected function execute(InputInterface $input, OutputInterface $output): int
@@ -58,9 +64,10 @@ protected function execute(InputInterface $input, OutputInterface $output): int
         $name = $input->getArgument('name');
         $allowEmpty = $input->getOption('allow-empty-diff') === true;
         $fromEmpty = $input->getOption('from-empty-schema') === true;
+        $dropIfExists = $input->getOption('drop-if-exists') === true ? true : null;
 
         try {
-            $version = $diffGenerator->generate($name, $allowEmpty, $fromEmpty);
+            $version = $diffGenerator->generate($name, $allowEmpty, $fromEmpty, $dropIfExists);
         } catch (MigrationException $e) {
             $io->warning($e->getMessage());
 

src/bridge/symfony/postgresql-bundle/src/Flow/Bridge/Symfony/PostgreSqlBundle/FlowPostgreSqlBundle.php

@@ -357,6 +357,10 @@ public function configure(DefinitionConfigurator $definition): void
             ->defaultTrue()
             ->info('Generate rollback files when creating migrations (default: true)')
             ->end()
+            ->booleanNode('drop_if_exists')
+            ->defaultFalse()
+            ->info('Emit IF EXISTS on diff-generated DROP statements (default: false)')
+            ->end()
             ->arrayNode('exclude')
             ->info('Schema objects excluded from migration diffing (e.g. tables created dynamically at runtime). Each entry defines exactly one matcher: schema, table, exact, starts_with, ends_with, pattern or policy_id.')
             ->arrayPrototype()
@@ -424,7 +428,7 @@ public function configure(DefinitionConfigurator $definition): void
     }
 
     /**
-     * @param array{connections: array<string, array{dsn: string, dbname: ?string, host: ?string, port: ?int, user: ?string, password: ?string, dbname_suffix: string, test_transaction_rollback: bool, context?: array<string, mixed>, telemetry?: array{service_id: string, clock_service_id: ?string, trace_queries: bool, trace_transactions: bool, collect_metrics: bool, log_queries: bool, max_query_length: int, include_parameters: bool, max_parameters: int, max_parameter_length: int}}>, messenger: array{enabled: bool, table_name: string, schema: string}, cache: array{pools?: array<string, array{connection: ?string, table_name: string, schema: string, id_col: string, data_col: string, lifetime_col: string, time_col: string, namespace: string, default_lifetime: int, marshaller_service_id: ?string, share_connection: bool}>}, session: array{enabled: bool, connection: ?string, table_name: string, schema: string, id_col: string, data_col: string, lifetime_col: string, time_col: string, lock_mode: string, ttl: ?int, share_connection: bool}, migrations: array{enabled: bool, directory: string, namespace: string, table_name: string, table_schema: string, migration_file_name: string, rollback_file_name: string, all_or_nothing: bool, generate_rollback: bool, exclude?: list<array{schema: ?string, table: ?string, exact: ?string, starts_with: ?string, ends_with: ?string, pattern: ?string, policy_id: ?string, type: ?string, for_schema: ?string}>}, catalog_providers: list<array{catalog_provider_id: ?string, catalog: ?array<string, mixed>}>} $config
+     * @param array{connections: array<string, array{dsn: string, dbname: ?string, host: ?string, port: ?int, user: ?string, password: ?string, dbname_suffix: string, test_transaction_rollback: bool, context?: array<string, mixed>, telemetry?: array{service_id: string, clock_service_id: ?string, trace_queries: bool, trace_transactions: bool, collect_metrics: bool, log_queries: bool, max_query_length: int, include_parameters: bool, max_parameters: int, max_parameter_length: int}}>, messenger: array{enabled: bool, table_name: string, schema: string}, cache: array{pools?: array<string, array{connection: ?string, table_name: string, schema: string, id_col: string, data_col: string, lifetime_col: string, time_col: string, namespace: string, default_lifetime: int, marshaller_service_id: ?string, share_connection: bool}>}, session: array{enabled: bool, connection: ?string, table_name: string, schema: string, id_col: string, data_col: string, lifetime_col: string, time_col: string, lock_mode: string, ttl: ?int, share_connection: bool}, migrations: array{enabled: bool, directory: string, namespace: string, table_name: string, table_schema: string, migration_file_name: string, rollback_file_name: string, all_or_nothing: bool, generate_rollback: bool, drop_if_exists: bool, exclude?: list<array{schema: ?string, table: ?string, exact: ?string, starts_with: ?string, ends_with: ?string, pattern: ?string, policy_id: ?string, type: ?string, for_schema: ?string}>}, catalog_providers: list<array{catalog_provider_id: ?string, catalog: ?array<string, mixed>}>} $config
      */
     #[Override]
     public function loadExtension(array $config, ContainerConfigurator $configurator, ContainerBuilder $container): void
@@ -666,7 +670,7 @@ private function registerMessenger(
     }
 
     /**
-     * @param array{enabled: bool, directory: string, namespace: string, table_name: string, table_schema: string, migration_file_name: string, rollback_file_name: string, all_or_nothing: bool, generate_rollback: bool, exclude?: list<array{schema: ?string, table: ?string, exact: ?string, starts_with: ?string, ends_with: ?string, pattern: ?string, policy_id: ?string, type: ?string, for_schema: ?string}>} $mc
+     * @param array{enabled: bool, directory: string, namespace: string, table_name: string, table_schema: string, migration_file_name: string, rollback_file_name: string, all_or_nothing: bool, generate_rollback: bool, drop_if_exists: bool, exclude?: list<array{schema: ?string, table: ?string, exact: ?string, starts_with: ?string, ends_with: ?string, pattern: ?string, policy_id: ?string, type: ?string, for_schema: ?string}>} $mc
      */
     private function registerMigrations(string $name, array $mc, ContainerBuilder $container, bool $isFirst): void
     {
@@ -684,6 +688,7 @@ private function registerMigrations(string $name, array $mc, ContainerBuilder $c
             $mc['all_or_nothing'],
             $mc['generate_rollback'],
             $this->buildExclusionPolicy($mc['exclude'] ?? []),
+            $mc['drop_if_exists'],
         ]);
         $configDef->setPublic(true);
         $container->setDefinition("flow.postgresql.{$name}.migrations.configuration", $configDef);

src/bridge/symfony/postgresql-bundle/tests/Flow/Bridge/Symfony/PostgreSqlBundle/Tests/Integration/Command/DiffCommandTest.php

@@ -34,4 +34,19 @@ public function test_generates_schema_migration(): void
         static::assertStringContainsString('DROP TABLE', $rollbackContent);
         static::assertStringContainsString('implements Rollback', $rollbackContent);
     }
+
+    public function test_generates_schema_migration_with_drop_if_exists_flag(): void
+    {
+        $command = $this->context->command('flow.postgresql.command.diff');
+        $tester = new CommandTester($command);
+        $tester->execute(['name' => 'create_test_users_if_exists', '--drop-if-exists' => true]);
+
+        static::assertSame(Command::SUCCESS, $tester->getStatusCode());
+
+        $dirs = $this->context->migrationDirs('*_create_test_users_if_exists');
+        static::assertCount(1, $dirs);
+
+        $rollbackContent = $this->context->fileContent((string) $dirs[0] . '/rollback.php');
+        static::assertStringContainsString('DROP TABLE IF EXISTS', $rollbackContent);
+    }
 }

src/bridge/symfony/postgresql-bundle/tests/Flow/Bridge/Symfony/PostgreSqlBundle/Tests/Integration/FlowPostgreSqlExtensionTest.php

@@ -1151,6 +1151,7 @@ public function test_migration_configuration_values_propagated(): void
                         'namespace' => 'Custom\\Migrations',
                         'table_name' => 'custom_migrations_table',
                         'table_schema' => 'custom_schema',
+                        'drop_if_exists' => true,
                     ],
                     'catalog_providers' => [
                         ['catalog_provider_id' => 'test.catalog_provider'],
@@ -1166,6 +1167,7 @@ public function test_migration_configuration_values_propagated(): void
         static::assertSame('Custom\\Migrations', $configuration->migrationsNamespace);
         static::assertSame('custom_migrations_table', $configuration->tableName);
         static::assertSame('custom_schema', $configuration->tableSchema);
+        static::assertTrue($configuration->dropIfExists);
     }
 
     public function test_migration_generate_and_up_to_date_commands_registered(): void

src/bridge/symfony/postgresql-bundle/tests/Flow/Bridge/Symfony/PostgreSqlBundle/Tests/Unit/DependencyInjection/ConfigurationTest.php

@@ -402,6 +402,22 @@ public function test_migrations_default_values(): void
         static::assertSame('public', $config['migrations']['table_schema']);
         static::assertFalse($config['migrations']['all_or_nothing']);
         static::assertTrue($config['migrations']['generate_rollback']);
+        static::assertFalse($config['migrations']['drop_if_exists']);
+    }
+
+    public function test_migrations_drop_if_exists_can_be_enabled(): void
+    {
+        $config = $this->context->processConfig([
+            'connections' => [
+                'default' => ['dsn' => 'postgresql://user:pass@localhost:5432/db'],
+            ],
+            'migrations' => [
+                'enabled' => true,
+                'drop_if_exists' => true,
+            ],
+        ]);
+
+        static::assertTrue($config['migrations']['drop_if_exists']);
     }
 
     public function test_migrations_exclude_defaults_to_empty(): void

src/lib/postgresql/src/Flow/PostgreSql/DSL/schema.php

@@ -1958,8 +1958,14 @@ function catalog_comparator(
     ?RenameStrategy $renameStrategy = null,
     ?ViewDependencyResolver $viewDependencyResolver = null,
     ?ExecutionOrderStrategy $tableOrderStrategy = null,
+    bool $dropIfExists = false,
 ): CatalogComparator {
-    return CatalogComparator::create($renameStrategy, $viewDependencyResolver, $tableOrderStrategy);
+    return CatalogComparator::create(
+        $renameStrategy,
+        $viewDependencyResolver,
+        $tableOrderStrategy,
+        dropIfExists: $dropIfExists,
+    );
 }
 
 #[DocumentationDSL(module: Module::PG_QUERY, type: DSLType::HELPER)]

src/lib/postgresql/src/Flow/PostgreSql/Migrations/Configuration.php

@@ -22,5 +22,6 @@ public function __construct(
         public bool $allOrNothing = false,
         public bool $generateRollback = true,
         public ?ExclusionPolicy $exclusionPolicy = null,
+        public bool $dropIfExists = false,
     ) {}
 }

src/lib/postgresql/src/Flow/PostgreSql/Migrations/Generator/DiffMigrationGenerator.php

@@ -23,12 +23,16 @@ public function __construct(
         private bool $generateRollback = true,
     ) {}
 
-    public function generate(?string $name = null, bool $allowEmpty = false, bool $fromEmptySchema = false): Version
-    {
+    public function generate(
+        ?string $name = null,
+        bool $allowEmpty = false,
+        bool $fromEmptySchema = false,
+        ?bool $dropIfExists = null,
+    ): Version {
         $source = $fromEmptySchema ? new Catalog([]) : $this->sourceCatalog->get();
         $target = $this->targetCatalog->get();
 
-        $diff = $this->comparator->compare($source, $target);
+        $diff = $this->comparator->compare($source, $target, $dropIfExists);
 
         if ($diff->isEmpty() && !$allowEmpty) {
             throw MigrationException::noChangesDetected();
@@ -41,7 +45,7 @@ public function generate(?string $name = null, bool $allowEmpty = false, bool $f
         if ($this->generateRollback) {
             $downSql = array_map(
                 static fn(Sql $query) => $query->toSql(),
-                $this->comparator->compare($target, $this->sourceCatalog->get())->generate(),
+                $this->comparator->compare($target, $this->sourceCatalog->get(), $dropIfExists)->generate(),
             );
         }
 

src/lib/postgresql/src/Flow/PostgreSql/Migrations/MigrationsFactory.php

@@ -41,7 +41,7 @@ public function createDiffGenerator(MigrationGenerator $generator): DiffMigratio
         return new DiffMigrationGenerator(
             client_catalog_provider($this->configuration->client, exclusionPolicy: $exclusionPolicy),
             $this->configuration->targetCatalogProvider,
-            catalog_comparator(),
+            catalog_comparator(dropIfExists: $this->configuration->dropIfExists),
             $generator,
             $this->configuration->generateRollback,
         );

src/lib/postgresql/src/Flow/PostgreSql/Schema/Diff/CatalogComparator.php

@@ -31,6 +31,7 @@ public function __construct(
         private ExecutionOrderStrategy $materializedViewOrderStrategy = new MaterializedViewDependencyOrder(
             new Parser(),
         ),
+        private bool $dropIfExists = false,
     ) {}
 
     /**
@@ -44,6 +45,7 @@ public static function create(
         ?ExecutionOrderStrategy $tableOrderStrategy = null,
         ?ExecutionOrderStrategy $viewOrderStrategy = null,
         ?ExecutionOrderStrategy $materializedViewOrderStrategy = null,
+        bool $dropIfExists = false,
     ): self {
         $renameStrategy ??= new GreedySimilarityRenameStrategy(new SimilarTextStrategy());
         $constraintComparator = new ConstraintComparator();
@@ -64,16 +66,19 @@ public static function create(
                 $tableOrderStrategy,
                 $viewOrderStrategy,
                 $materializedViewOrderStrategy,
+                dropIfExists: $dropIfExists,
             ),
             $viewDependencyResolver ?? new AstViewDependencyResolver(new Parser()),
             $tableOrderStrategy,
             $viewOrderStrategy,
             $materializedViewOrderStrategy,
+            dropIfExists: $dropIfExists,
         );
     }
 
-    public function compare(Catalog $source, Catalog $target): CatalogDiff
+    public function compare(Catalog $source, Catalog $target, ?bool $dropIfExists = null): CatalogDiff
     {
+        $effectiveDropIfExists = $dropIfExists ?? $this->dropIfExists;
         $sourceNames = $source->names();
         $targetNames = $target->names();
 
@@ -98,7 +103,11 @@ public function compare(Catalog $source, Catalog $target): CatalogDiff
                 continue;
             }
 
-            $schemaDiff = $this->schemaComparator->compare($source->get($name), $target->get($name));
+            $schemaDiff = $this->schemaComparator->compare(
+                $source->get($name),
+                $target->get($name),
+                $effectiveDropIfExists,
+            );
 
             if (!$schemaDiff->isEmpty()) {
                 $modifiedSchemas[] = $schemaDiff;
@@ -115,6 +124,7 @@ public function compare(Catalog $source, Catalog $target): CatalogDiff
             $this->tableOrderStrategy,
             $this->viewOrderStrategy,
             $this->materializedViewOrderStrategy,
+            $effectiveDropIfExists,
         );
     }
 }

src/lib/postgresql/src/Flow/PostgreSql/Schema/Diff/CatalogDiff.php

@@ -48,6 +48,7 @@ public function __construct(
         private ExecutionOrderStrategy $materializedViewOrderStrategy = new MaterializedViewDependencyOrder(
             new Parser(),
         ),
+        private bool $dropIfExists = false,
     ) {}
 
     /**
@@ -72,9 +73,10 @@ public function generate(): array
         $dependentViews = $this->resolveDependentViews();
 
         foreach ($dependentViews->toDrop as $dv) {
-            $sqls[] = $dv->view instanceof MaterializedView
+            $builder = $dv->view instanceof MaterializedView
                 ? drop()->materializedView($dv->qualifiedName())
                 : drop()->view($dv->qualifiedName());
+            $sqls[] = $this->dropIfExists ? $builder->ifExists() : $builder;
         }
 
         foreach ($this->modifiedSchemas as $diff) {
@@ -109,7 +111,8 @@ public function generate(): array
         }
 
         foreach ($this->removedSchemas as $schema) {
-            $sqls[] = drop()->schema($schema->name)->cascade();
+            $builder = drop()->schema($schema->name)->cascade();
+            $sqls[] = $this->dropIfExists ? $builder->ifExists() : $builder;
         }
 
         return $sqls;