frontend-plugin-api: implement .T on route refs as declared props

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

packages/frontend-plugin-api/src/routing/RouteRef.test.ts

@@ -21,7 +21,7 @@ describe('RouteRef', () => {
   it('should be created and have a mutable ID', () => {
     const routeRef: RouteRef<undefined> = createRouteRef();
     const internal = toInternalRouteRef(routeRef);
-    expect(() => internal.T).toThrow();
+    expect(internal.T).toBe(undefined);
     expect(internal.getParams()).toEqual([]);
     expect(internal.getDescription()).toMatch(/RouteRef\.test\.ts/);
 
@@ -51,7 +51,6 @@ describe('RouteRef', () => {
     const internal = toInternalRouteRef(routeRef);
     expect(internal.getParams()).toEqual(['x', 'y']);
     expect(internal.getDescription()).toMatch(/RouteRef\.test\.ts/);
-    expect(() => internal.T).toThrow();
   });
 
   it('should properly infer and validate parameter types and assignments', () => {

packages/frontend-plugin-api/src/routing/RouteRef.ts

@@ -63,6 +63,7 @@ export function isRouteRef(opaque: { $$type: string }): opaque is RouteRef {
 export class RouteRefImpl implements InternalRouteRef {
   readonly $$type = '@backstage/RouteRef';
   readonly version = 'v1';
+  declare readonly T: never;
 
   #id?: string;
   #params: string[];
@@ -73,10 +74,6 @@ export class RouteRefImpl implements InternalRouteRef {
     this.#creationSite = creationSite;
   }
 
-  get T(): never {
-    throw new Error(`tried to read RouteRef.T of ${this}`);
-  }
-
   getParams(): string[] {
     return this.#params;
   }

packages/frontend-plugin-api/src/routing/SubRouteRef.test.ts

@@ -34,6 +34,7 @@ describe('SubRouteRef', () => {
     });
     const internal = toInternalSubRouteRef(routeRef);
     expect(internal.path).toBe('/foo');
+    expect(internal.T).toBe(undefined);
     expect(internal.getParent()).toBe(internalParent);
     expect(internal.getParams()).toEqual([]);
     expect(String(internal)).toMatch(

packages/frontend-plugin-api/src/routing/SubRouteRef.ts

@@ -73,6 +73,7 @@ export class SubRouteRefImpl<TParams extends AnyRouteParams>
 {
   readonly $$type = '@backstage/SubRouteRef';
   readonly version = 'v1';
+  declare readonly T: never;
 
   #params: string[];
   #parent: RouteRef;
@@ -82,10 +83,6 @@ export class SubRouteRefImpl<TParams extends AnyRouteParams>
     this.#parent = parent;
   }
 
-  get T(): never {
-    throw new Error(`tried to read RouteRef.T of ${this}`);
-  }
-
   getParams(): string[] {
     return this.#params;
   }