From b8b95c0cf836a44add19524f7deb63cbaba182e7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Miika=20H=C3=A4nninen?= <miika.hanninen@gmail.com>
Date: Tue, 2 Oct 2018 21:34:46 +0300
Subject: [PATCH]  ramda: Workaround for type inference problem in Filter
 (#28592)

* ramda: add return type assertions for filter/reject test

* ramda: Add failing test for filter-in-pipe scenario

* ramda: Workaround for type inference problem in Filter

In the `Filter` type, when used inside a pipe, the second format always took
precedence in type inference, causing problems when a list was filtered.

With this change, you can manually specify whether you are using filter
for an array or an object, so usage in a pipe will work. You can also
leave out the second type parameter, in which case filter works as
previously.

```ts
import { pipe, filter } from 'ramda';

pipe(
    filter<string, 'array'>((val: string) => val.length > 2),
)(['list', 'or', 'object']);

pipe(
    filter<string, 'object'>((val) => val.length > 2),
)({ a: 'list', b: 'or', c: 'object' });
```
---
 types/ramda/index.d.ts     | 22 +++++++++++++---------
 types/ramda/ramda-tests.ts | 30 ++++++++++++++++++++++++++----
 2 files changed, 39 insertions(+), 13 deletions(-)

diff --git a/types/ramda/index.d.ts b/types/ramda/index.d.ts
index 05e84e721f..9623aa8865 100644
--- a/types/ramda/index.d.ts
+++ b/types/ramda/index.d.ts
@@ -80,9 +80,17 @@ declare namespace R {
         set<T, U>(str: string, obj: T): U;
     }
 
-    interface Filter<T> {
-      (list: ReadonlyArray<T>): T[];
-      (obj: Dictionary<T>): Dictionary<T>;
+    interface Filter {
+        <T>(fn: (value: T) => boolean): FilterOnceApplied<T>;
+        <T, Kind extends 'array'>(fn: (value: T) => boolean): (list: ReadonlyArray<T>) => T[];
+        <T, Kind extends 'object'>(fn: (value: T) => boolean): (list: Dictionary<T>) => Dictionary<T>;
+        <T>(fn: (value: T) => boolean, list: ReadonlyArray<T>): T[];
+        <T>(fn: (value: T) => boolean, obj: Dictionary<T>): Dictionary<T>;
+    }
+
+    interface FilterOnceApplied<T> {
+        (list: ReadonlyArray<T>): T[];
+        (obj: Dictionary<T>): Dictionary<T>;
     }
 
     type Evolve<O extends Evolvable<E>, E extends Evolver> = {
@@ -721,9 +729,7 @@ declare namespace R {
         /**
          * Returns a new list containing only those items that match a given predicate function. The predicate function is passed one argument: (value).
          */
-        filter<T>(fn: (value: T) => boolean): Filter<T>;
-        filter<T>(fn: (value: T) => boolean, list: ReadonlyArray<T>): T[];
-        filter<T>(fn: (value: T) => boolean, obj: Dictionary<T>): Dictionary<T>;
+        filter: Filter;
 
         /**
          * Returns the first element of the list which matches the predicate, or `undefined` if no
@@ -1906,9 +1912,7 @@ declare namespace R {
          * Similar to `filter`, except that it keeps only values for which the given predicate
          * function returns falsy.
          */
-        reject<T>(fn: (value: T) => boolean): Filter<T>;
-        reject<T>(fn: (value: T) => boolean, list: ReadonlyArray<T>): T[];
-        reject<T>(fn: (value: T) => boolean, obj: Dictionary<T>): Dictionary<T>;
+        reject: Filter;
 
         /**
          * Removes the sub-list of `list` starting at index `start` and containing `count` elements.
diff --git a/types/ramda/ramda-tests.ts b/types/ramda/ramda-tests.ts
index 73ba908fd5..951c11ba02 100644
--- a/types/ramda/ramda-tests.ts
+++ b/types/ramda/ramda-tests.ts
@@ -695,12 +695,34 @@ R.times(i, 5);
     }
 
     const filterEven = R.filter(isEven);
-    filterEven({ a: 0, b: 1 }); // => { a: 0 }
-    filterEven([0, 1]); // => [0]
+    const objA: R.Dictionary<number> = filterEven({ a: 0, b: 1 }); // => { a: 0 }
+    const listA: number[] = filterEven([0, 1]); // => [0]
 
     const rejectEven = R.reject(isEven);
-    rejectEven({ a: 0, b: 1 }); // => { b: 1 }
-    rejectEven([0, 1]); // => [1]
+    const objB: R.Dictionary<number> = rejectEven({ a: 0, b: 1 }); // => { b: 1 }
+    const listB: number[] = rejectEven([0, 1]); // => [1]
+};
+
+() => {
+    function isEven(n: number) {
+        return n % 2 === 0;
+    }
+
+    const a: R.Dictionary<number> = R.pipe(
+        R.filter<number, 'object'>(isEven),
+    )({ a: 0, b: 1 }); // => { a: 0 }
+
+    const b: number[] = R.pipe(
+        R.filter<number, 'array'>(isEven),
+    )([0, 1]); // => [0]
+
+    const c: R.Dictionary<number> = R.pipe(
+        R.reject<number, 'object'>(isEven),
+    )({ a: 0, b: 1 }); // => { b: 1 }
+
+    const d: number[] = R.pipe(
+        R.reject<number, 'array'>(isEven),
+    )([0, 1]); // => [1]
 };
 
 () => {