ImageSource: Convert ImageURISource to Interface

Summary:
Changes the `ImageURISource` Flow type into an interface.

- This enables both objects and class instances to be subtypes of `ImageURISource`.
- This makes it invalid to spread `ImageURISource` as a type, so `interface X extends ImageURISource` can instead be used.
- This makes it invalid to spread `ImageURISource` as a value, so `getImageSourceProperties(x)` can instead be used.
- This makes it invalid to use `$Exact` with `ImageURISource`.

Changelog:
[General][Changed] - `ImageURISource` Flow type is now an interface instead of an object.

Reviewed By: timrc

Differential Revision: D29323508

fbshipit-source-id: 647c2f9b0bfead6d7e56bdb7108e623cbf8b6c89

Libraries/Image/ImageSource.js

@@ -16,39 +16,39 @@
  * This type is intentinoally inexact in order to permit call sites that supply
  * extra properties.
  */
-export type ImageURISource = $ReadOnly<{
+export interface ImageURISource {
   /**
    * `uri` is a string representing the resource identifier for the image, which
    * could be an http address, a local file path, or the name of a static image
    * resource (which should be wrapped in the `require('./path/to/image.png')`
    * function).
    */
-  uri?: ?string,
+  +uri?: ?string;
 
   /**
    * `bundle` is the iOS asset bundle which the image is included in. This
    * will default to [NSBundle mainBundle] if not set.
    * @platform ios
    */
-  bundle?: ?string,
+  +bundle?: ?string;
 
   /**
    * `method` is the HTTP Method to use. Defaults to GET if not specified.
    */
-  method?: ?string,
+  +method?: ?string;
 
   /**
    * `headers` is an object representing the HTTP headers to send along with the
    * request for a remote image.
    */
-  headers?: ?{[string]: string},
+  +headers?: ?{[string]: string};
 
   /**
    * `body` is the HTTP body to send with the request. This must be a valid
    * UTF-8 string, and will be sent exactly as specified, with no
    * additional encoding (e.g. URL-escaping or base64) applied.
    */
-  body?: ?string,
+  +body?: ?string;
 
   /**
    * `cache` determines how the requests handles potentially cached
@@ -70,25 +70,68 @@ export type ImageURISource = $ReadOnly<{
    *
    * @platform ios
    */
-  cache?: ?('default' | 'reload' | 'force-cache' | 'only-if-cached'),
+  +cache?: ?('default' | 'reload' | 'force-cache' | 'only-if-cached');
 
   /**
    * `width` and `height` can be specified if known at build time, in which case
    * these will be used to set the default `<Image/>` component dimensions.
    */
-  width?: ?number,
-  height?: ?number,
+  +width?: ?number;
+  +height?: ?number;
 
   /**
    * `scale` is used to indicate the scale factor of the image. Defaults to 1.0 if
    * unspecified, meaning that one image pixel equates to one display point / DIP.
    */
-  scale?: ?number,
-
-  ...
-}>;
+  +scale?: ?number;
+}
 
 export type ImageSource =
   | number
   | ImageURISource
   | $ReadOnlyArray<ImageURISource>;
+
+export function getImageSourceProperties(
+  imageSource: ImageURISource,
+): $ReadOnly<{
+  body?: ?string,
+  bundle?: ?string,
+  cache?: ?('default' | 'reload' | 'force-cache' | 'only-if-cached'),
+  headers?: ?{[string]: string},
+  height?: ?number,
+  method?: ?string,
+  scale?: ?number,
+  uri?: ?string,
+  width?: ?number,
+  ...
+}> {
+  const object = {};
+  if (imageSource.body != null) {
+    object.body = imageSource.body;
+  }
+  if (imageSource.bundle != null) {
+    object.bundle = imageSource.bundle;
+  }
+  if (imageSource.cache != null) {
+    object.cache = imageSource.cache;
+  }
+  if (imageSource.headers != null) {
+    object.headers = imageSource.headers;
+  }
+  if (imageSource.height != null) {
+    object.height = imageSource.height;
+  }
+  if (imageSource.method != null) {
+    object.method = imageSource.method;
+  }
+  if (imageSource.scale != null) {
+    object.scale = imageSource.scale;
+  }
+  if (imageSource.uri != null) {
+    object.uri = imageSource.uri;
+  }
+  if (imageSource.width != null) {
+    object.width = imageSource.width;
+  }
+  return object;
+}