From 6058a95955643828268d0eac55615d6ecf15cd5b Mon Sep 17 00:00:00 2001
From: Patrik Oldsberg <poldsberg@gmail.com>
Date: Tue, 6 Aug 2024 14:13:23 +0200
Subject: [PATCH] backend-plugin-api: backwards compat for service ref multiton
 field

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>
---
 packages/backend-plugin-api/api-report.md      |  2 +-
 .../src/services/system/types.test.ts          | 18 ++++++++++++++++++
 .../src/services/system/types.ts               |  4 ++--
 3 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/packages/backend-plugin-api/api-report.md b/packages/backend-plugin-api/api-report.md
index 99c7b1b9fc..16574ac94e 100644
--- a/packages/backend-plugin-api/api-report.md
+++ b/packages/backend-plugin-api/api-report.md
@@ -703,7 +703,7 @@ export type ServiceRef<
 > = {
   id: string;
   scope: TScope;
-  multiton: TInstances extends 'multiton' ? true : false;
+  multiton?: TInstances extends 'multiton' ? true : false;
   T: TService;
   $$type: '@backstage/ServiceRef';
 };
diff --git a/packages/backend-plugin-api/src/services/system/types.test.ts b/packages/backend-plugin-api/src/services/system/types.test.ts
index adf097761b..70d165fd8d 100644
--- a/packages/backend-plugin-api/src/services/system/types.test.ts
+++ b/packages/backend-plugin-api/src/services/system/types.test.ts
@@ -324,6 +324,24 @@ describe('createServiceFactory', () => {
     metaFactory();
   });
 
+  it('should support old service refs without a multiton field', () => {
+    const oldPluginDep = pluginDep as Omit<typeof pluginDep, 'multiton'>; // Old refs don't have a multiton field
+    const metaFactory = createServiceFactory({
+      service: ref,
+      deps: {
+        plugin: oldPluginDep,
+      },
+      async factory({ plugin }) {
+        const plugin1: boolean = plugin;
+        // @ts-expect-error
+        const plugin2: number = plugin;
+        unused(plugin1, plugin2);
+        return 'x';
+      },
+    });
+    expect(metaFactory).toEqual(expect.any(Function));
+  });
+
   it('should only allow objects as options', () => {
     // @ts-expect-error
     const metaFactory = createServiceFactory((_opts: string) => ({
diff --git a/packages/backend-plugin-api/src/services/system/types.ts b/packages/backend-plugin-api/src/services/system/types.ts
index 7cd18da4d2..a6f33d7941 100644
--- a/packages/backend-plugin-api/src/services/system/types.ts
+++ b/packages/backend-plugin-api/src/services/system/types.ts
@@ -39,7 +39,7 @@ export type ServiceRef<
    */
   scope: TScope;
 
-  multiton: TInstances extends 'multiton' ? true : false;
+  multiton?: TInstances extends 'multiton' ? true : false;
 
   /**
    * Utility for getting the type of the service, using `typeof serviceRef.T`.
@@ -189,7 +189,7 @@ type ServiceRefsToInstances<
 > = {
   [key in keyof T as T[key]['scope'] extends TScope
     ? key
-    : never]: T[key]['multiton'] extends true
+    : never]: T[key]['multiton'] extends true | undefined
     ? Array<T[key]['T']>
     : T[key]['T'];
 };