fix(Observable): correct typings issues in pipe

Allows specific types of Observables to be passed through (as in ReactiveX#2972),
and also prevents incorrect typings from falling through to ellipsis
function due to the use of `any`.

Closes ReactiveX#2972

src/internal/Observable.ts

@@ -1,7 +1,7 @@
 import { Operator } from './Operator';
 import { Subscriber } from './Subscriber';
 import { Subscription } from './Subscription';
-import { TeardownLogic, OperatorFunction, PartialObserver, Subscribable } from './types';
+import { TeardownLogic, PartialObserver, Subscribable, UnaryFunction } from './types';
 import { toSubscriber } from './util/toSubscriber';
 import { iif } from './observable/iif';
 import { throwError } from './observable/throwError';
@@ -287,16 +287,16 @@ export class Observable<T> implements Subscribable<T> {
 
   /* tslint:disable:max-line-length */
   pipe(): Observable<T>;
-  pipe<A>(op1: OperatorFunction<T, A>): Observable<A>;
-  pipe<A, B>(op1: OperatorFunction<T, A>, op2: OperatorFunction<A, B>): Observable<B>;
-  pipe<A, B, C>(op1: OperatorFunction<T, A>, op2: OperatorFunction<A, B>, op3: OperatorFunction<B, C>): Observable<C>;
-  pipe<A, B, C, D>(op1: OperatorFunction<T, A>, op2: OperatorFunction<A, B>, op3: OperatorFunction<B, C>, op4: OperatorFunction<C, D>): Observable<D>;
-  pipe<A, B, C, D, E>(op1: OperatorFunction<T, A>, op2: OperatorFunction<A, B>, op3: OperatorFunction<B, C>, op4: OperatorFunction<C, D>, op5: OperatorFunction<D, E>): Observable<E>;
-  pipe<A, B, C, D, E, F>(op1: OperatorFunction<T, A>, op2: OperatorFunction<A, B>, op3: OperatorFunction<B, C>, op4: OperatorFunction<C, D>, op5: OperatorFunction<D, E>, op6: OperatorFunction<E, F>): Observable<F>;
-  pipe<A, B, C, D, E, F, G>(op1: OperatorFunction<T, A>, op2: OperatorFunction<A, B>, op3: OperatorFunction<B, C>, op4: OperatorFunction<C, D>, op5: OperatorFunction<D, E>, op6: OperatorFunction<E, F>, op7: OperatorFunction<F, G>): Observable<G>;
-  pipe<A, B, C, D, E, F, G, H>(op1: OperatorFunction<T, A>, op2: OperatorFunction<A, B>, op3: OperatorFunction<B, C>, op4: OperatorFunction<C, D>, op5: OperatorFunction<D, E>, op6: OperatorFunction<E, F>, op7: OperatorFunction<F, G>, op8: OperatorFunction<G, H>): Observable<H>;
-  pipe<A, B, C, D, E, F, G, H, I>(op1: OperatorFunction<T, A>, op2: OperatorFunction<A, B>, op3: OperatorFunction<B, C>, op4: OperatorFunction<C, D>, op5: OperatorFunction<D, E>, op6: OperatorFunction<E, F>, op7: OperatorFunction<F, G>, op8: OperatorFunction<G, H>, op9: OperatorFunction<H, I>): Observable<I>;
-  pipe<R>(...operations: OperatorFunction<any, any>[]): Observable<R>;
+  pipe<A>(op1: UnaryFunction<Observable<T>, A>): A;
+  pipe<A, B>(op1: UnaryFunction<Observable<T>, A>, op2: UnaryFunction<A, B>): B;
+  pipe<A, B, C>(op1: UnaryFunction<Observable<T>, A>, op2: UnaryFunction<A, B>, op3: UnaryFunction<B, C>): C;
+  pipe<A, B, C, D>(op1: UnaryFunction<Observable<T>, A>, op2: UnaryFunction<A, B>, op3: UnaryFunction<B, C>, op4: UnaryFunction<C, D>): D;
+  pipe<A, B, C, D, E>(op1: UnaryFunction<Observable<T>, A>, op2: UnaryFunction<A, B>, op3: UnaryFunction<B, C>, op4: UnaryFunction<C, D>, op5: UnaryFunction<D, E>): E;
+  pipe<A, B, C, D, E, F>(op1: UnaryFunction<Observable<T>, A>, op2: UnaryFunction<A, B>, op3: UnaryFunction<B, C>, op4: UnaryFunction<C, D>, op5: UnaryFunction<D, E>, op6: UnaryFunction<E, F>): F;
+  pipe<A, B, C, D, E, F, G>(op1: UnaryFunction<Observable<T>, A>, op2: UnaryFunction<A, B>, op3: UnaryFunction<B, C>, op4: UnaryFunction<C, D>, op5: UnaryFunction<D, E>, op6: UnaryFunction<E, F>, op7: UnaryFunction<F, G>): G;
+  pipe<A, B, C, D, E, F, G, H>(op1: UnaryFunction<Observable<T>, A>, op2: UnaryFunction<A, B>, op3: UnaryFunction<B, C>, op4: UnaryFunction<C, D>, op5: UnaryFunction<D, E>, op6: UnaryFunction<E, F>, op7: UnaryFunction<F, G>, op8: UnaryFunction<G, H>): H;
+  pipe<A, B, C, D, E, F, G, H, I>(op1: UnaryFunction<Observable<T>, A>, op2: UnaryFunction<A, B>, op3: UnaryFunction<B, C>, op4: UnaryFunction<C, D>, op5: UnaryFunction<D, E>, op6: UnaryFunction<E, F>, op7: UnaryFunction<F, G>, op8: UnaryFunction<G, H>, op9: UnaryFunction<H, I>): I;
+  pipe<A, B, C, D, E, F, G, H, I, R>(op1: UnaryFunction<Observable<T>, A>, op2: UnaryFunction<A, B>, op3: UnaryFunction<B, C>, op4: UnaryFunction<C, D>, op5: UnaryFunction<D, E>, op6: UnaryFunction<E, F>, op7: UnaryFunction<F, G>, op8: UnaryFunction<G, H>, op9: UnaryFunction<H, I>, ...operations: UnaryFunction<any, any>[]): R;
   /* tslint:enable:max-line-length */
 
   /**
@@ -318,7 +318,7 @@ export class Observable<T> implements Subscribable<T> {
    *   .subscribe(x => console.log(x))
    * ```
    */
-  pipe<R>(...operations: OperatorFunction<T, R>[]): Observable<R> {
+  pipe<R>(...operations: UnaryFunction<Observable<T>, R>[]): R {
     if (operations.length === 0) {
       return this as any;
     }