core-api: refactor global singleton access to get/set/getOrCreate

Co-authored-by: Juan Lulkin <jmaiz@spotify.com>
Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

packages/core-api/src/extensions/componentData.tsx

@@ -15,7 +15,7 @@
  */
 
 import { ComponentType, ReactNode } from 'react';
-import { getGlobalSingleton } from '../lib/globalObject';
+import { getOrCreateGlobalSingleton } from '../lib/globalObject';
 
 // TODO(Rugvip): Access via symbol is deprecated, remove once on 0.3.x
 const DATA_KEY = Symbol('backstage-component-data');
@@ -33,7 +33,7 @@ type MaybeComponentNode = ReactNode & {
 };
 
 // The store is bridged across versions using the global object
-const store = getGlobalSingleton(
+const store = getOrCreateGlobalSingleton(
   'component-data-store',
   () => new WeakMap<ComponentType<any>, DataContainer>(),
 );

packages/core-api/src/lib/globalObject.test.ts

@@ -14,7 +14,11 @@
  * limitations under the License.
  */
 
-import { getGlobalSingleton } from './globalObject';
+import {
+  getGlobalSingleton,
+  getOrCreateGlobalSingleton,
+  setGlobalSingleton,
+} from './globalObject';
 
 const anyGlobal = global as any;
 
@@ -23,20 +27,64 @@ describe('getGlobalSingleton', () => {
     delete anyGlobal['__@backstage/my-thing__'];
   });
 
+  it('should return an existing value', () => {
+    const myThing = {};
+    const myOtherThing = {};
+
+    anyGlobal['__@backstage/my-thing__'] = myThing;
+    expect(getGlobalSingleton('my-thing')).toBe(myThing);
+    expect(getGlobalSingleton('my-thing')).toBe(myThing);
+    anyGlobal['__@backstage/my-thing__'] = myOtherThing;
+    expect(getGlobalSingleton('my-thing')).toBe(myOtherThing);
+  });
+
+  it('should throw if the value is not set', () => {
+    expect(() => getGlobalSingleton('my-thing')).toThrow(
+      'Global my-thing is not set',
+    );
+  });
+});
+
+describe('getOrCreateGlobalSingleton', () => {
+  beforeEach(() => {
+    delete anyGlobal['__@backstage/my-thing__'];
+  });
+
   it('should return an existing value', () => {
     const myThing = {};
     anyGlobal['__@backstage/my-thing__'] = myThing;
 
-    expect(getGlobalSingleton('my-thing', () => ({}))).toBe(myThing);
-    expect(getGlobalSingleton('my-thing', () => ({}))).toBe(myThing);
+    expect(getOrCreateGlobalSingleton('my-thing', () => ({}))).toBe(myThing);
+    expect(getOrCreateGlobalSingleton('my-thing', () => ({}))).toBe(myThing);
   });
 
   it('should should create a new value', () => {
     const myNewThing = {};
 
     expect(anyGlobal['__@backstage/my-thing__']).toBe(undefined);
-    expect(getGlobalSingleton('my-thing', () => myNewThing)).toBe(myNewThing);
+    expect(getOrCreateGlobalSingleton('my-thing', () => myNewThing)).toBe(
+      myNewThing,
+    );
     expect(anyGlobal['__@backstage/my-thing__']).toBe(myNewThing);
-    expect(getGlobalSingleton('my-thing', () => ({}))).toBe(myNewThing);
+    expect(getOrCreateGlobalSingleton('my-thing', () => ({}))).toBe(myNewThing);
+  });
+});
+
+describe('setGlobalSingleton', () => {
+  beforeEach(() => {
+    delete anyGlobal['__@backstage/my-thing__'];
+  });
+
+  it('should set a global value', () => {
+    setGlobalSingleton('my-thing', 'global value');
+
+    expect(anyGlobal['__@backstage/my-thing__']).toBe('global value');
+  });
+
+  it('should throw if global value is set', () => {
+    anyGlobal['__@backstage/my-thing__'] = 'already defined';
+    expect(() => setGlobalSingleton('my-thing', () => 'global value')).toThrow(
+      'Global my-thing is already se',
+    );
   });
 });

packages/core-api/src/lib/globalObject.ts

@@ -26,10 +26,41 @@ function getGlobalObject() {
   return Function('return this')();
 }
 
-export const globalObject = getGlobalObject();
+const globalObject = getGlobalObject();
 
-export function getGlobalSingleton<T>(id: string, supplier: () => T): T {
-  const key = `__@backstage/${id}__`;
+const makeKey = (id: string) => `__@backstage/${id}__`;
+
+/**
+ * Used to provide a global singleton value, failing if it is already set.
+ */
+export function setGlobalSingleton(id: string, value: unknown): void {
+  const key = makeKey(id);
+  if (key in globalObject) {
+    throw new Error(`Global ${id} is already set`); // TODO some sort of special build err
+  }
+  globalObject[key] = value;
+}
+
+/**
+ * Used to access a global singleton value, failing if it is not already set.
+ */
+export function getGlobalSingleton<T>(id: string): T {
+  const key = makeKey(id);
+  if (!(key in globalObject)) {
+    throw new Error(`Global ${id} is not set`); // TODO some sort of special build err
+  }
+
+  return globalObject[key];
+}
+
+/**
+ * Serializes access to a global singleton value, with the first caller creating the value.
+ */
+export function getOrCreateGlobalSingleton<T>(
+  id: string,
+  supplier: () => T,
+): T {
+  const key = makeKey(id);
 
   let value = globalObject[key];
   if (value) {

packages/core-api/src/routing/types.ts

@@ -15,7 +15,7 @@
  */
 
 import { IconComponent } from '../icons';
-import { getGlobalSingleton } from '../lib/globalObject';
+import { getOrCreateGlobalSingleton } from '../lib/globalObject';
 
 export type AnyParams = { [param in string]: string } | undefined;
 export type ParamKeys<Params extends AnyParams> = keyof Params extends never
@@ -34,7 +34,7 @@ export type RouteFunc<Params extends AnyParams> = (
   ...[params]: Params extends undefined ? readonly [] : readonly [Params]
 ) => string;
 
-export const routeRefType: unique symbol = getGlobalSingleton<any>(
+export const routeRefType: unique symbol = getOrCreateGlobalSingleton<any>(
   'route-ref-type',
   () => Symbol('route-ref-type'),
 );