Fix alterTable without legacy alter table

Closes #3088

drift/CHANGELOG.md

@@ -1,6 +1,7 @@
 ## 2.22.1
 
 - Fix generated SQL for `insertFromSelect` statements with upserts.
+- Fix `alterTable` for databases where `legacy_alter_table` is not writable.
 
 ## 2.22.0
 

drift/lib/src/runtime/query_builder/migration.dart

@@ -158,7 +158,7 @@ class Migrator {
     final foreignKeysEnabled =
         (await database.customSelect('PRAGMA foreign_keys').getSingle())
             .read<bool>('foreign_keys');
-    final legacyAlterTable =
+    bool? legacyAlterTable =
         (await database.customSelect('PRAGMA legacy_alter_table').getSingle())
             .read<bool>('legacy_alter_table');
 
@@ -255,16 +255,39 @@ class Migrator {
       // we've just dropped the original table), we need to enable the legacy
       // option which skips the integrity check.
       // See also: https://sqlite.org/forum/forumpost/0e2390093fbb8fd6
-      if (!legacyAlterTable) {
-        await _issueCustomQuery('pragma legacy_alter_table = 1;');
+      if (legacyAlterTable == false) {
+        try {
+          await _issueCustomQuery('pragma legacy_alter_table = 1;');
+        } on Object {
+          // On some databases like Turso, legacy_alter_table is not writable.
+          legacyAlterTable = null;
+
+          // A workaround is to drop all views and to re-create them later.
+          // We're not doing this by default to ensure we're not breaking
+          // existing users (e.g. if the new table references a view somehow).
+          final allViews = await database.customSelect(
+            'SELECT name, sql FROM sqlite_master WHERE type = ?;',
+            variables: [Variable<String>('view')],
+          ).get();
+
+          for (final row in allViews) {
+            final sql = row.read<String>('sql');
+            if (!createAffected.contains(sql)) {
+              createAffected.add(sql);
+            }
+
+            final name = row.read<String>('name');
+            await database.customStatement('DROP VIEW "$name";');
+          }
+        }
       }
 
       // Step 7: Rename the new table to the old name
       await _issueCustomQuery(
           'ALTER TABLE ${context.identifier(temporaryName)} '
           'RENAME TO ${context.identifier(tableName)}');
 
-      if (!legacyAlterTable) {
+      if (legacyAlterTable == false) {
         await _issueCustomQuery('pragma legacy_alter_table = 0;');
       }
 

drift/test/integration_tests/migrations_integration_test.dart

@@ -534,6 +534,19 @@ void main() {
 
     expect(underlying.userVersion, 3);
   });
+
+  test("alterTable works for databases that can't set legacy alter table",
+      () async {
+    final interceptor = _NoLegacyAlterTable();
+    final db = TodoDb(NativeDatabase.memory().interceptWith(interceptor));
+    addTearDown(db.close);
+
+    final user = await db.users.insertReturning(
+        UsersCompanion.insert(name: 'test user', profilePicture: Uint8List(0)));
+    await Migrator(db).alterTable(TableMigration(db.users));
+    expect(await db.users.all().get(), [user]);
+    expect(interceptor.didPreventLegacyAlterTable, isTrue);
+  });
 }
 
 class _TestDatabase extends GeneratedDatabase {
@@ -548,3 +561,18 @@ class _TestDatabase extends GeneratedDatabase {
   @override
   final MigrationStrategy migration;
 }
+
+class _NoLegacyAlterTable extends QueryInterceptor {
+  var didPreventLegacyAlterTable = false;
+
+  @override
+  Future<void> runCustom(
+      QueryExecutor executor, String statement, List<Object?> args) {
+    if (statement.contains('legacy_alter_table') && statement.contains('=')) {
+      didPreventLegacyAlterTable = true;
+      throw 'not allowed';
+    }
+
+    return super.runCustom(executor, statement, args);
+  }
+}