fix(distinctUntilKeyChanged): improved key typing with keyof T (#3988)

* fix(distinctUntilKeyChanged): correct signatures

* chore(distinctUntilKeyChanged): nail down key's typing with keyof T

compat/operator/distinctUntilKeyChanged.ts

@@ -3,8 +3,8 @@ import { Observable } from 'rxjs';
 import { distinctUntilKeyChanged as higherOrder } from 'rxjs/operators';
 
 /* tslint:disable:max-line-length */
-export function distinctUntilKeyChanged<T>(this: Observable<T>, key: string): Observable<T>;
-export function distinctUntilKeyChanged<T, K>(this: Observable<T>, key: string, compare: (x: K, y: K) => boolean): Observable<T>;
+export function distinctUntilKeyChanged<T>(this: Observable<T>, key: keyof T): Observable<T>;
+export function distinctUntilKeyChanged<T, K extends keyof T>(this: Observable<T>, key: K, compare: (x: T[K], y: T[K]) => boolean): Observable<T>;
 /* tslint:enable:max-line-length */
 
 /**
@@ -64,6 +64,7 @@ export function distinctUntilKeyChanged<T, K>(this: Observable<T>, key: string,
  * @method distinctUntilKeyChanged
  * @owner Observable
  */
-export function distinctUntilKeyChanged<T>(this: Observable<T>, key: string, compare?: (x: T, y: T) => boolean): Observable<T> {
-  return higherOrder<T, T>(key, compare)(this);
+// tslint:disable-next-line:max-line-length
+export function distinctUntilKeyChanged<T, K extends keyof T>(this: Observable<T>, key: K, compare?: (x: T[K], y: T[K]) => boolean): Observable<T> {
+  return higherOrder<T, K>(key, compare)(this);
 }

spec-dtslint/operators/distinctUntilKeyChanged-spec.ts

@@ -0,0 +1,20 @@
+import { of } from 'rxjs';
+import { distinctUntilKeyChanged } from 'rxjs/operators';
+
+const sample = {name: 'foobar', num: 42};
+
+it('should enforce key set', () => {
+  const o = of(sample).pipe(distinctUntilKeyChanged('something')); // $ExpectError
+});
+
+it('should enforce key set with compare', () => {
+  const o = of(sample).pipe(distinctUntilKeyChanged('something', () => true)); // $ExpectError
+});
+
+it("should enforce compare's type", () => {
+  const o = of(sample).pipe(distinctUntilKeyChanged('name', (a: number, b: number) => true)); // $ExpectError
+});
+
+it("should enforce key set and compare's type", () => {
+  const o = of(sample).pipe(distinctUntilKeyChanged('something', (a: number, b: number) => true)); // $ExpectError
+});

spec/operators/distinctUntilKeyChanged-spec.ts

@@ -185,7 +185,7 @@ describe('distinctUntilKeyChanged operator', () => {
     const e1subs =   '^                !';
     const expected = '--a--------------|';
 
-    expectObservable((<any>e1).pipe(distinctUntilKeyChanged('val', () => true))).toBe(expected, values);
+    expectObservable(e1.pipe(distinctUntilKeyChanged('val', () => true))).toBe(expected, values);
     expectSubscriptions(e1.subscriptions).toBe(e1subs);
   });
 
@@ -195,7 +195,7 @@ describe('distinctUntilKeyChanged operator', () => {
     const e1subs =   '^                   !';
     const expected = '--a--a--a--a--a--a--|';
 
-    expectObservable((<any>e1).pipe(distinctUntilKeyChanged('val', () => false))).toBe(expected, values);
+    expectObservable(e1.pipe(distinctUntilKeyChanged('val', () => false))).toBe(expected, values);
     expectSubscriptions(e1.subscriptions).toBe(e1subs);
   });
 
@@ -206,7 +206,7 @@ describe('distinctUntilKeyChanged operator', () => {
     const expected = '--a-----c-----e--|';
     const selector = (x: number, y: number) => y % 2 === 0;
 
-    expectObservable((<any>e1).pipe(distinctUntilKeyChanged('val', selector))).toBe(expected, values);
+    expectObservable(e1.pipe(distinctUntilKeyChanged('val', selector))).toBe(expected, values);
     expectSubscriptions(e1.subscriptions).toBe(e1subs);
   });
 
@@ -222,7 +222,7 @@ describe('distinctUntilKeyChanged operator', () => {
       return x === y;
     };
 
-    expectObservable((<any>e1).pipe(distinctUntilKeyChanged('val', selector))).toBe(expected, values);
+    expectObservable(e1.pipe(distinctUntilKeyChanged('val', selector))).toBe(expected, values);
     expectSubscriptions(e1.subscriptions).toBe(e1subs);
   });
 });

src/internal/operators/distinctUntilKeyChanged.ts

@@ -2,8 +2,8 @@ import { distinctUntilChanged } from './distinctUntilChanged';
 import { MonoTypeOperatorFunction } from '../types';
 
 /* tslint:disable:max-line-length */
-export function distinctUntilKeyChanged<T>(key: string): MonoTypeOperatorFunction<T>;
-export function distinctUntilKeyChanged<T, K>(key: string, compare: (x: K, y: K) => boolean): MonoTypeOperatorFunction<T>;
+export function distinctUntilKeyChanged<T>(key: keyof T): MonoTypeOperatorFunction<T>;
+export function distinctUntilKeyChanged<T, K extends keyof T>(key: K, compare: (x: T[K], y: T[K]) => boolean): MonoTypeOperatorFunction<T>;
 /* tslint:enable:max-line-length */
 
 /**
@@ -70,6 +70,6 @@ export function distinctUntilKeyChanged<T, K>(key: string, compare: (x: K, y: K)
  * @method distinctUntilKeyChanged
  * @owner Observable
  */
-export function distinctUntilKeyChanged<T>(key: string, compare?: (x: T, y: T) => boolean): MonoTypeOperatorFunction<T> {
+export function distinctUntilKeyChanged<T, K extends keyof T>(key: K, compare?: (x: T[K], y: T[K]) => boolean): MonoTypeOperatorFunction<T> {
   return distinctUntilChanged((x: T, y: T) => compare ? compare(x[key], y[key]) : x[key] === y[key]);
 }