From 4fef8e2c33bceafa814ad41363404b883c48884b Mon Sep 17 00:00:00 2001
From: Oliver Joseph Ash <oliverjash@gmail.com>
Date: Tue, 21 Jan 2020 15:13:53 +0000
Subject: [PATCH] `react`: `Children` fixes (#41760)

* `react`: `Children.map` fixes

https://reactjs.org/docs/react-api.html#reactchildren

* Refine return type

* Apply same changes to `toArray`
---
 types/react/index.d.ts    | 6 ++++--
 types/react/test/index.ts | 8 ++++++--
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/types/react/index.d.ts b/types/react/index.d.ts
index 5528f267ba..2112f615b0 100644
--- a/types/react/index.d.ts
+++ b/types/react/index.d.ts
@@ -2788,11 +2788,13 @@ declare namespace React {
     // ----------------------------------------------------------------------
 
     interface ReactChildren {
-        map<T, C>(children: C | C[], fn: (child: C, index: number) => T): T[];
+        map(children: null, fn: (child: never, index: number) => never): null;
+        map(children: undefined, fn: (child: never, index: number) => never): undefined;
+        map<T, C>(children: C | C[], fn: (child: C, index: number) => T): Array<Exclude<T, boolean | null | undefined>>;
         forEach<C>(children: C | C[], fn: (child: C, index: number) => void): void;
         count(children: any): number;
         only<C>(children: C): C extends any[] ? never : C;
-        toArray<C>(children: C | C[]): C[];
+        toArray(children: ReactNode | ReactNode[]): Array<Exclude<ReactNode, boolean | null | undefined>>;
     }
 
     //
diff --git a/types/react/test/index.ts b/types/react/test/index.ts
index f501e44ce4..4ee1c6caa2 100644
--- a/types/react/test/index.ts
+++ b/types/react/test/index.ts
@@ -511,7 +511,7 @@ React.Children.forEach(children, (child) => { });
 const nChildren: number = React.Children.count(children);
 let onlyChild: React.ReactElement = React.Children.only(DOM.div()); // ok
 onlyChild = React.Children.only([null, [[["Hallo"], true]], false]); // error
-const childrenToArray: React.ReactChild[] = React.Children.toArray(children);
+const childrenToArray: Array<Exclude<React.ReactNode, boolean | null | undefined>> = React.Children.toArray(children);
 
 declare const numberChildren: number[];
 declare const elementChildren: JSX.Element[];
@@ -519,13 +519,17 @@ declare const mixedChildren: Array<JSX.Element | string>;
 declare const singlePluralChildren: JSX.Element | JSX.Element[];
 declare const renderPropsChildren: () => JSX.Element;
 
+// $ExpectType null
+const mappedChildrenArray0 = React.Children.map(null, num => num);
+// $ExpectType undefined
+const mappedChildrenArray1 = React.Children.map(undefined, num => num);
 // $ExpectType number[]
 const mappedChildrenArray2 = React.Children.map(numberChildren, num => num);
 // $ExpectType Element[]
 const mappedChildrenArray3 = React.Children.map(elementChildren, element => element);
 // $ExpectType (string | Element)[]
 const mappedChildrenArray4 = React.Children.map(mixedChildren, elementOrString => elementOrString);
-// $ExpectType (string | number | null)[]
+// $ExpectType Key[]
 const mappedChildrenArray5 = React.Children.map(singlePluralChildren, element => element.key);
 // $ExpectType string[]
 const mappedChildrenArray6 = React.Children.map(renderPropsChildren, element => element.name);