ignore `instance.actor` when checking if there are local users (#13146)

* ignore `instance.actor` when checking if there are local users

We've seen this happen a few times:

* there was some AP software at $some_domain
* it gets replaced by Misskey
* before the first user can be created, an AP activity comes in
* Misskey resolves the activity
* to do this, it creates the `instance.actor` to sign its request
* now there *is* a local user, so the `meta` endpoint returns
  `requireSetup:false`
* the admin is very confused

This commit factors out the check, and doesn't count the
`instance.actor` as a real user.

* autogen bits

2 files changed, 12 insertions, 2 deletions

diff --git a/packages/backend/src/core/InstanceActorService.ts b/packages/backend/src/core/InstanceActorService.ts
index b40fd46291..7ce8dc96a1 100644
--- a/packages/backend/src/core/InstanceActorService.ts
+++ b/packages/backend/src/core/InstanceActorService.ts
@@ -4,7 +4,7 @@
  */
 
 import { Inject, Injectable } from '@nestjs/common';
-import { IsNull } from 'typeorm';
+import { IsNull, Not } from 'typeorm';
 import type { MiLocalUser } from '@/models/User.js';
 import type { UsersRepository } from '@/models/_.js';
 import { MemorySingleCache } from '@/misc/cache.js';
@@ -28,6 +28,14 @@ export class InstanceActorService {
 	}
 
 	@bindThis
+	public async realLocalUsersPresent(): Promise<boolean> {
+		return await this.usersRepository.existsBy({
+			host: IsNull(),
+			username: Not(ACTOR_USERNAME),
+		});
+	}
+
+	@bindThis
 	public async getInstanceActor(): Promise<MiLocalUser> {
 		const cached = this.cache.get();
 		if (cached) return cached;
diff --git a/packages/backend/src/core/SignupService.ts b/packages/backend/src/core/SignupService.ts
index b9e3ded46f..81c2b241eb 100644
--- a/packages/backend/src/core/SignupService.ts
+++ b/packages/backend/src/core/SignupService.ts
@@ -16,6 +16,7 @@ import { MiUserKeypair } from '@/models/UserKeypair.js';
 import { MiUsedUsername } from '@/models/UsedUsername.js';
 import generateUserToken from '@/misc/generate-native-user-token.js';
 import { UserEntityService } from '@/core/entities/UserEntityService.js';
+import { InstanceActorService } from '@/core/InstanceActorService.js';
 import { bindThis } from '@/decorators.js';
 import UsersChart from '@/core/chart/charts/users.js';
 import { UtilityService } from '@/core/UtilityService.js';
@@ -37,6 +38,7 @@ export class SignupService {
 		private userEntityService: UserEntityService,
 		private idService: IdService,
 		private metaService: MetaService,
+		private instanceActorService: InstanceActorService,
 		private usersChart: UsersChart,
 	) {
 	}
@@ -81,7 +83,7 @@ export class SignupService {
 			throw new Error('USED_USERNAME');
 		}
 
-		const isTheFirstUser = (await this.usersRepository.countBy({ host: IsNull() })) === 0;
+		const isTheFirstUser = !await this.instanceActorService.realLocalUsersPresent();
 
 		if (!opts.ignorePreservedUsernames && !isTheFirstUser) {
 			const instance = await this.metaService.fetch(true);