fix: use empty object type in combineLatest/forkJoin sigs (#5832)

* test: add failing dtslint tests

* fix: use empty object type

* chore: improve test descriptions

* chore: remove accidental whitespace

* chore: spelling

* chore: remove tslint line-length comment

* chore: rebase properly

* chore: update api_guardian

api_guard/dist/types/index.d.ts

@@ -43,7 +43,9 @@ export declare function bindNodeCallback<A extends readonly unknown[], R extends
 export declare function combineLatest(sources: []): Observable<never>;
 export declare function combineLatest<A extends readonly unknown[]>(sources: readonly [...ObservableInputTuple<A>]): Observable<A>;
 export declare function combineLatest<A extends readonly unknown[]>(...sources: [...ObservableInputTuple<A>]): Observable<A>;
-export declare function combineLatest(sourcesObject: {}): Observable<never>;
+export declare function combineLatest(sourcesObject: {
+    [K in any]: never;
+}): Observable<never>;
 export declare function combineLatest<T>(sourcesObject: T): Observable<{
     [K in keyof T]: ObservedValueOf<T[K]>;
 }>;
@@ -166,7 +168,9 @@ export declare function firstValueFrom<T>(source: Observable<T>): Promise<T>;
 export declare function forkJoin(sources: []): Observable<never>;
 export declare function forkJoin<A extends readonly unknown[]>(sources: readonly [...ObservableInputTuple<A>]): Observable<A>;
 export declare function forkJoin<A extends readonly unknown[]>(...sources: [...ObservableInputTuple<A>]): Observable<A>;
-export declare function forkJoin(sourcesObject: {}): Observable<never>;
+export declare function forkJoin(sourcesObject: {
+    [K in any]: never;
+}): Observable<never>;
 export declare function forkJoin<T>(sourcesObject: T): Observable<{
     [K in keyof T]: ObservedValueOf<T[K]>;
 }>;

spec-dtslint/observables/combineLatest-spec.ts

@@ -136,4 +136,9 @@ describe('combineLatest({})', () => {
   it('should work for the simple case', () => {
     const res = combineLatest({ foo: a$, bar: b$, baz: c$ }); // $ExpectType Observable<{ foo: A; bar: B; baz: C; }>
   });
+
+  it('should not rely upon the excess-properties behavior to identify empty objects', () => {
+    const obj = { foo: a$, bar: b$, baz: c$ };
+    const res = combineLatest(obj); // $ExpectType Observable<{ foo: A; bar: B; baz: C; }>
+  });
 });

spec-dtslint/observables/forkJoin-spec.ts

@@ -67,6 +67,11 @@ describe('forkJoin({})', () => {
   it('should work for the simple case', () => {
     const res = forkJoin({ foo: of(1), bar: of('two'), baz: of(false) }); // $ExpectType Observable<{ foo: number; bar: string; baz: boolean; }>
   });
+
+  it('should not rely upon the excess-properties behavior to identify empty objects', () => {
+    const obj = { foo: of(1), bar: of('two'), baz: of(false) };
+    const res = forkJoin(obj); // $ExpectType Observable<{ foo: number; bar: string; baz: boolean; }>
+  });
 });
 
 describe('forkJoin([])', () => {

src/internal/observable/combineLatest.ts

@@ -18,7 +18,7 @@ export function combineLatest<A extends readonly unknown[]>(sources: readonly [.
 export function combineLatest<A extends readonly unknown[]>(...sources: [...ObservableInputTuple<A>]): Observable<A>;
 
 // combineLatest({a, b, c})
-export function combineLatest(sourcesObject: {}): Observable<never>;
+export function combineLatest(sourcesObject: { [K in any]: never }): Observable<never>;
 export function combineLatest<T>(sourcesObject: T): Observable<{ [K in keyof T]: ObservedValueOf<T[K]> }>;
 
 // If called with a single array, it "auto-spreads" the array, with result selector

src/internal/observable/forkJoin.ts

@@ -15,12 +15,11 @@ export function forkJoin<A extends readonly unknown[]>(sources: readonly [...Obs
 export function forkJoin<A extends readonly unknown[]>(...sources: [...ObservableInputTuple<A>]): Observable<A>;
 
 // forkJoin({a, b, c})
-export function forkJoin(sourcesObject: {}): Observable<never>;
+export function forkJoin(sourcesObject: { [K in any]: never }): Observable<never>;
 export function forkJoin<T>(sourcesObject: T): Observable<{ [K in keyof T]: ObservedValueOf<T[K]> }>;
 
 // forkJoin(a, b, c, resultSelector)
 /** @deprecated resultSelector is deprecated, pipe to map instead */
-
 export function forkJoin(...args: Array<ObservableInput<any> | ((...args: any[]) => any)>): Observable<any>;
 
 /**