From a6fd2ee6ac80beb78401c12181c81a597f44fa36 Mon Sep 17 00:00:00 2001
From: Ferdy Budhidharma <ferd312@gmail.com>
Date: Wed, 16 Jan 2019 01:30:26 -0600
Subject: [PATCH] [react] better prop typing for JS users (#32182)

* better prop resolutions

* lint rules
---
 types/react/index.d.ts                 | 23 ++++++++++++++++++----
 types/react/test/managedAttributes.tsx | 27 ++++++++++++++++++++++++++
 2 files changed, 46 insertions(+), 4 deletions(-)

diff --git a/types/react/index.d.ts b/types/react/index.d.ts
index 11d879b2ff..a1e851314d 100644
--- a/types/react/index.d.ts
+++ b/types/react/index.d.ts
@@ -491,6 +491,10 @@ declare namespace React {
         getDefaultProps?(): P;
     }
 
+    type JSXElementConstructor<P> =
+        | ((props: P) => ReactElement<any> | null)
+        | (new (props: P) => Component<P, any>);
+
     /**
      * We use an intersection type to infer multiple type parameters from
      * a single argument, which is useful for many top-level API defs.
@@ -719,8 +723,8 @@ declare namespace React {
      * NOTE: prefer ComponentPropsWithRef, if the ref is forwarded,
      * or ComponentPropsWithoutRef when refs are not supported.
      */
-    type ComponentProps<T extends ReactType> =
-        T extends ComponentType<infer P>
+    type ComponentProps<T extends keyof JSX.IntrinsicElements | JSXElementConstructor<any>> =
+        T extends JSXElementConstructor<infer P>
             ? P
             : T extends keyof JSX.IntrinsicElements
                 ? JSX.IntrinsicElements[T]
@@ -2629,9 +2633,20 @@ declare namespace React {
     }
 }
 
-// Declared props take priority over inferred props
+// naked 'any' type in a conditional type will short circuit and union both the then/else branches
+// so boolean is only resolved for T = any
+type IsExactlyAny<T> = boolean extends (T extends never ? true : false) ? true : false;
+
+// Try to resolve ill-defined props like for JS users: props can be any, or sometimes objects with properties of type any
+// If props is type any, use propTypes definitions, otherwise for each `any` property of props, use the propTypes type
 // If declared props have indexed properties, ignore inferred props entirely as keyof gets widened
-type MergePropTypes<P, T> = P & Pick<T, Exclude<keyof T, keyof P>>;
+type MergePropTypes<P, T> = IsExactlyAny<P> extends true ? T : ({
+    [K in keyof P]: IsExactlyAny<P[K]> extends true
+        ? K extends keyof T
+        ? T[K]
+        : P[K]
+        : P[K]
+} & Pick<T, Exclude<keyof T, keyof P>>);
 
 // Any prop that has a default prop becomes optional, but its type is unchanged
 // Undeclared default props are augmented into the resulting allowable attributes
diff --git a/types/react/test/managedAttributes.tsx b/types/react/test/managedAttributes.tsx
index 1e0e8226d9..9939cffb15 100644
--- a/types/react/test/managedAttributes.tsx
+++ b/types/react/test/managedAttributes.tsx
@@ -222,3 +222,30 @@ interface LeaveMeAloneDtslint { foo: string; }
 //     // $ExpectError the type of ForwardRef.defaultProps stays Partial<P> anyway even if assigned
 //     <ForwardRef str='abc' />
 // ];
+
+// const weakComponentPropTypes = {
+//     foo: PropTypes.string,
+//     bar: PropTypes.bool.isRequired
+// };
+// interface WeakComponentProps1 {
+//     foo: any;
+//     bar: number;
+// }
+// interface WeakComponentProps2 {
+//     foo: string;
+//     bar: any;
+// }
+
+// // $ExpectType true
+// type weakComponentTest1 = JSX.LibraryManagedAttributes<{ propTypes: typeof weakComponentPropTypes }, any> extends {
+//     foo?: string | null
+//     bar: boolean
+// } ? true : false;
+// type weakComponentTest2 = JSX.LibraryManagedAttributes<{ propTypes: typeof weakComponentPropTypes }, WeakComponentProps1> extends {
+//     foo?: string | null
+//     bar: number
+// } ? true : false;
+// type weakComponentTest3 = JSX.LibraryManagedAttributes<{ propTypes: typeof weakComponentPropTypes }, WeakComponentProps2> extends {
+//     foo: string
+//     bar: boolean
+// } ? true : false;