fix(pipe): Ensure that unknown is infered for 9+ arguments. (#6212)

Author: benlesh

api_guard/dist/types/index.d.ts

@@ -336,7 +336,7 @@ export declare function pipe<T, A, B, C, D, E, F>(fn1: UnaryFunction<T, A>, fn2:
 export declare function pipe<T, A, B, C, D, E, F, G>(fn1: UnaryFunction<T, A>, fn2: UnaryFunction<A, B>, fn3: UnaryFunction<B, C>, fn4: UnaryFunction<C, D>, fn5: UnaryFunction<D, E>, fn6: UnaryFunction<E, F>, fn7: UnaryFunction<F, G>): UnaryFunction<T, G>;
 export declare function pipe<T, A, B, C, D, E, F, G, H>(fn1: UnaryFunction<T, A>, fn2: UnaryFunction<A, B>, fn3: UnaryFunction<B, C>, fn4: UnaryFunction<C, D>, fn5: UnaryFunction<D, E>, fn6: UnaryFunction<E, F>, fn7: UnaryFunction<F, G>, fn8: UnaryFunction<G, H>): UnaryFunction<T, H>;
 export declare function pipe<T, A, B, C, D, E, F, G, H, I>(fn1: UnaryFunction<T, A>, fn2: UnaryFunction<A, B>, fn3: UnaryFunction<B, C>, fn4: UnaryFunction<C, D>, fn5: UnaryFunction<D, E>, fn6: UnaryFunction<E, F>, fn7: UnaryFunction<F, G>, fn8: UnaryFunction<G, H>, fn9: UnaryFunction<H, I>): UnaryFunction<T, I>;
-export declare function pipe<T, A, B, C, D, E, F, G, H, I>(fn1: UnaryFunction<T, A>, fn2: UnaryFunction<A, B>, fn3: UnaryFunction<B, C>, fn4: UnaryFunction<C, D>, fn5: UnaryFunction<D, E>, fn6: UnaryFunction<E, F>, fn7: UnaryFunction<F, G>, fn8: UnaryFunction<G, H>, fn9: UnaryFunction<H, I>, ...fns: UnaryFunction<any, any>[]): UnaryFunction<T, {}>;
+export declare function pipe<T, A, B, C, D, E, F, G, H, I>(fn1: UnaryFunction<T, A>, fn2: UnaryFunction<A, B>, fn3: UnaryFunction<B, C>, fn4: UnaryFunction<C, D>, fn5: UnaryFunction<D, E>, fn6: UnaryFunction<E, F>, fn7: UnaryFunction<F, G>, fn8: UnaryFunction<G, H>, fn9: UnaryFunction<H, I>, ...fns: UnaryFunction<any, any>[]): UnaryFunction<T, unknown>;
 
 export declare const queue: QueueScheduler;
 

spec-dtslint/util/pipe-spec.ts

@@ -61,8 +61,8 @@ it('should infer for 9 arguments', () => {
   const o = pipe(a('0', '1'), a('1', '2'), a('2', '3'), a('3', '4'), a('4', '5'), a('5', '6'), a('6', '7'), a('7', '8'), a('8', '9')); // $ExpectType UnaryFunction<"0", "9">
 });
 
-it('should infer {} for more than 9 arguments', () => {
-  const o =  pipe(a('0', '1'), a('1', '2'), a('2', '3'), a('3', '4'), a('4', '5'), a('5', '6'), a('6', '7'), a('7', '8'), a('8', '9'), a('9', '10'));  // $ExpectType UnaryFunction<"0", {}>
+it('should infer unknown for more than 9 arguments', () => {
+  const o =  pipe(a('0', '1'), a('1', '2'), a('2', '3'), a('3', '4'), a('4', '5'), a('5', '6'), a('6', '7'), a('7', '8'), a('8', '9'), a('9', '10'));  // $ExpectType UnaryFunction<"0", unknown>
 });
 
 it('should require a type assertion for more than 9 arguments', () => {

src/internal/util/pipe.ts

@@ -1,7 +1,6 @@
 import { identity } from './identity';
 import { UnaryFunction } from '../types';
 
-/* tslint:disable:max-line-length */
 export function pipe(): typeof identity;
 export function pipe<T, A>(fn1: UnaryFunction<T, A>): UnaryFunction<T, A>;
 export function pipe<T, A, B>(fn1: UnaryFunction<T, A>, fn2: UnaryFunction<A, B>): UnaryFunction<T, B>;
@@ -68,8 +67,7 @@ export function pipe<T, A, B, C, D, E, F, G, H, I>(
   fn8: UnaryFunction<G, H>,
   fn9: UnaryFunction<H, I>,
   ...fns: UnaryFunction<any, any>[]
-): UnaryFunction<T, {}>;
-/* tslint:enable:max-line-length */
+): UnaryFunction<T, unknown>;
 
 export function pipe(...fns: Array<UnaryFunction<any, any>>): UnaryFunction<any, any> {
   return pipeFromArray(fns);