Create type utility EntryPointElementConfig

Reviewed By: rbalicki2

Differential Revision: D24191021

fbshipit-source-id: ddd50ce144e0cf4623ac916ba8361fed6b3be32e

Author: vikr01

packages/relay-experimental/EntryPointTypes.flow.js

@@ -210,6 +210,24 @@ export type PreloadedEntryPoint<TEntryPointComponent> = $ReadOnly<{|
   rootModuleID: string,
 |}>;
 
+type _ComponentFromEntryPoint = <
+  +TPreloadParams,
+  +TComponent,
+  +TEntryPoint: EntryPoint<TPreloadParams, TComponent>,
+>(
+  TEntryPoint,
+) => TComponent;
+
+type ComponentFromEntryPoint<+TEntryPoint> = $Call<
+  _ComponentFromEntryPoint,
+  TEntryPoint,
+>;
+
+export type EntryPointElementConfig<+TEntryPoint> = $PropertyType<
+  ElementConfig<ComponentFromEntryPoint<TEntryPoint>>,
+  'props',
+>;
+
 export type ThinQueryParams<
   TQuery: OperationType,
   TEnvironmentProviderOptions,

packages/relay-experimental/__flowtests__/EntryPointTypes-flowtest.js

@@ -0,0 +1,47 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @emails oncall+relay
+ * @flow strict-local
+ * @format
+ */
+
+'use strict';
+
+import type {
+  EntryPoint,
+  EntryPointProps,
+  EntryPointElementConfig,
+} from '../EntryPointTypes.flow';
+
+type MyComponentOtherProps = $ReadOnly<{|
+  foo: string,
+|}>;
+
+type MyComponentProps = EntryPointProps<{}, {}, MyComponentOtherProps, {}>;
+
+const MyComponent = (_props: MyComponentProps) => null;
+
+type PreloadParams = $ReadOnly<{||}>;
+
+type MyComponentEntryPointType = EntryPoint<PreloadParams, typeof MyComponent>;
+
+// This gets the "other props" of the component through the entrypoint's typing
+type MyComponentEntryPointProps = EntryPointElementConfig<MyComponentEntryPointType>;
+
+// This gets the "other props" directly from the component's prop typings
+type OtherProps = $PropertyType<MyComponentProps, 'props'>;
+
+// We want to make sure that `OtherProps` and `MyComponentEntryPointProps` are exactly the same.
+opaque type __SUBTYPE_CHECK_1__: OtherProps = MyComponentEntryPointProps;
+opaque type __SUBTYPE_CHECK_2__: MyComponentEntryPointProps = OtherProps;
+
+({foo: ''}: OtherProps);
+
+({foo: ''}: MyComponentEntryPointProps);
+
+// $FlowExpectedError[incompatible-cast]
+({foo: null}: MyComponentEntryPointProps);