fix(migrator): store snapshot only after migration is generated (#5470)

### The problem
When using custom migration fileName function which forces using name
(throws) as in the example in documentaion
https://mikro-orm.io/docs/migrations#using-custom-migration-names and
having snapshots enabled, causes the update of snapshot. Second retry
with using name is not generating migration, because the snapshot has
already been updated and no changes are found.

 ```typescript
 migrations: {
  fileName: (timestamp: string, name?: string) => {
// force user to provide the name, otherwise you would end up with
`Migration20230421212713_undefined`
    if (!name) {
throw new Error('Specify migration name via `mikro-orm migration:create
--name=...`');
    }

    return `Migration${timestamp}_${name}`;
  },
  snapshot: true,
},
 ```

### Description of the solution
Delaying update of snapshot after migration file is actually generated.
Thus, updating it only after successful call to
`this.generator.generate` which, under the hood, calls custom `fileName`
function which is throwing error.

packages/migrations/src/Migrator.ts

@@ -80,8 +80,9 @@ export class Migrator implements IMigrator {
       return { fileName: '', code: '', diff };
     }
 
-    await this.storeCurrentSchema();
     const migration = await this.generator.generate(diff, path, name);
+    await this.storeCurrentSchema();
+
     return {
       fileName: migration[1],
       code: migration[0],
@@ -102,8 +103,8 @@ export class Migrator implements IMigrator {
     await this.ensureMigrationsDirExists();
     const schemaExists = await this.validateInitialMigration();
     const diff = await this.getSchemaDiff(false, true);
-    await this.storeCurrentSchema();
     const migration = await this.generator.generate(diff, path, name);
+    await this.storeCurrentSchema();
 
     if (schemaExists) {
       await this.storage.logMigration({ name: migration[1], context: null });

tests/features/migrations/Migrator.test.ts

@@ -107,6 +107,38 @@ describe('Migrator', () => {
     downMock.mockRestore();
   });
 
+  test('snapshot should not be updated when custom migration fileName function throws', async () => {
+    const dateMock = jest.spyOn(Date.prototype, 'toISOString');
+    dateMock.mockReturnValue('2019-10-13T21:48:13.382Z');
+    const migrationsSettings = orm.config.get('migrations');
+    orm.config.set('migrations', {
+      ...migrationsSettings,
+      fileName: (timestamp, name?) => {
+        if (!name) {
+          throw new Error('Migration name is required');
+        }
+
+        return `migration-${timestamp}-${name}`;
+      },
+      snapshot: true,
+    });
+    const migrator = orm.migrator;
+    await expect(migrator.createMigration()).rejects.toThrow(
+      'Migration name is required',
+    );
+    // retry creating migration with specified name
+    const migration = await migrator.createMigration(
+      undefined,
+      false,
+      false,
+      'with-custom-name',
+    );
+    expect(migration.fileName).toEqual('migration-20191013214813-with-custom-name.ts');
+    expect(migration).toMatchSnapshot('migration-dump');
+    orm.config.set('migrations', migrationsSettings); // Revert migration config changes
+    await remove(process.cwd() + '/temp/migrations-123/' + migration.fileName);
+  });
+
   test('generate schema migration', async () => {
     const dateMock = jest.spyOn(Date.prototype, 'toISOString');
     dateMock.mockReturnValue('2019-10-13T21:48:13.382Z');

tests/features/migrations/__snapshots__/Migrator.test.ts.snap

@@ -822,6 +822,52 @@ export class Migration20191013214813 extends Migration {
 }
 `;
 
+exports[`Migrator snapshot should not be updated when custom migration fileName function throws: migration-dump 1`] = `
+{
+  "code": "import { Migration } from '@mikro-orm/migrations';
+
+export class Migration20191013214813_with-custom-name extends Migration {
+
+  async up(): Promise<void> {
+    this.addSql('alter table \`test2\` drop foreign key \`test2_foo___bar_foreign\`;');
+
+    this.addSql('alter table \`book2\` drop column \`foo\`;');
+
+    this.addSql('alter table \`test2\` drop index \`test2_foo___bar_unique\`;');
+    this.addSql('alter table \`test2\` drop column \`foo___bar\`, drop column \`foo___baz\`;');
+  }
+
+  async down(): Promise<void> {
+    this.addSql('alter table \`book2\` add \`foo\` varchar(255) null default \\'lol\\';');
+
+    this.addSql('alter table \`test2\` add \`foo___bar\` int unsigned null, add \`foo___baz\` int unsigned null;');
+    this.addSql('alter table \`test2\` add constraint \`test2_foo___bar_foreign\` foreign key (\`foo___bar\`) references \`foo_bar2\` (\`id\`) on update cascade on delete set null;');
+    this.addSql('alter table \`test2\` add unique \`test2_foo___bar_unique\`(\`foo___bar\`);');
+  }
+
+}
+",
+  "diff": {
+    "down": [
+      "alter table \`book2\` add \`foo\` varchar(255) null default 'lol';",
+      "",
+      "alter table \`test2\` add \`foo___bar\` int unsigned null, add \`foo___baz\` int unsigned null;",
+      "alter table \`test2\` add constraint \`test2_foo___bar_foreign\` foreign key (\`foo___bar\`) references \`foo_bar2\` (\`id\`) on update cascade on delete set null;",
+      "alter table \`test2\` add unique \`test2_foo___bar_unique\`(\`foo___bar\`);",
+    ],
+    "up": [
+      "alter table \`test2\` drop foreign key \`test2_foo___bar_foreign\`;",
+      "",
+      "alter table \`book2\` drop column \`foo\`;",
+      "",
+      "alter table \`test2\` drop index \`test2_foo___bar_unique\`;",
+      "alter table \`test2\` drop column \`foo___bar\`, drop column \`foo___baz\`;",
+    ],
+  },
+  "fileName": "migration-20191013214813-with-custom-name.ts",
+}
+`;
+
 exports[`Migrator up/down params [all or nothing disabled]: all-or-nothing-disabled 1`] = `
 [
   "select 1 from information_schema.schemata where schema_name = 'mikro_orm_test_migrations' (via write connection '127.0.0.1')",