Reduce rerendering on startup (#12847)

* Ensure viewport data store changes happen immediately on startup.

We need to call `flush`, so that the changes happen synchronously,
rather than asynchronously, on the next event loop.
This avoids the re-rendering of all `BlockListBlock` instances
during startup.

* Ensure `state.hasUploadPermissions` is always a boolean.

The reducer for this property defaults to an empty object, which
not only is incorrect (since this is a boolean), but also causes
unnecessary re-renders by changing reference. By defaulting to
`true` instead, we fix both problems.

* Add a couple of tests for hasUploadPermissions reducer.

* Core Data: Add CHANGELOG entry for hasUplaodPermissions boolean fix

* Viewport: Add CHANGELOG entry for synchronous assignment

packages/core-data/CHANGELOG.md

@@ -1,3 +1,9 @@
+## 2.0.16 (Unreleased)
+
+### Bug Fixes
+
+- Fixed the `hasUploadPermissions` selector to always return a boolean. Previously, it may have returned an empty object. This should have no impact for most consumers, assuming usage as a [truthy value](https://developer.mozilla.org/en-US/docs/Glossary/Truthy) in conditions.
+
 ## 2.0.15 (2018-12-12)
 
 ## 2.0.14 (2018-11-20)

packages/core-data/src/reducer.js

@@ -225,7 +225,7 @@ export function embedPreviews( state = {}, action ) {
  *
  * @return {Object} Updated state.
  */
-export function hasUploadPermissions( state = {}, action ) {
+export function hasUploadPermissions( state = true, action ) {
 	switch ( action.type ) {
 		case 'RECEIVE_UPLOAD_PERMISSIONS':
 			return action.hasUploadPermissions;

packages/core-data/src/test/reducer.js

@@ -7,7 +7,7 @@ import { filter } from 'lodash';
 /**
  * Internal dependencies
  */
-import { terms, entities, embedPreviews } from '../reducer';
+import { terms, entities, embedPreviews, hasUploadPermissions } from '../reducer';
 
 describe( 'terms()', () => {
 	it( 'returns an empty object by default', () => {
@@ -117,3 +117,22 @@ describe( 'embedPreviews()', () => {
 		} );
 	} );
 } );
+
+describe( 'hasUploadPermissions()', () => {
+	it( 'returns true by default', () => {
+		const state = hasUploadPermissions( undefined, {} );
+
+		expect( state ).toEqual( true );
+	} );
+
+	it( 'returns with updated upload permissions value', () => {
+		const originalState = true;
+
+		const state = hasUploadPermissions( originalState, {
+			type: 'RECEIVE_UPLOAD_PERMISSIONS',
+			hasUploadPermissions: false,
+		} );
+
+		expect( state ).toEqual( false );
+	} );
+} );

packages/viewport/CHANGELOG.md

@@ -1,3 +1,9 @@
+## 2.1.0 (Unreleased)
+
+### Improvements
+
+- The initial viewport state is assigned synchronously, rather than on the next process tick. This should have an impact of fewer callbacks made to data subscribers.
+
 ## 2.0.13 (2018-12-12)
 
 ## 2.0.12 (2018-11-20)

packages/viewport/src/index.js

@@ -76,3 +76,4 @@ window.addEventListener( 'orientationchange', setIsMatching );
 
 // Set initial values
 setIsMatching();
+setIsMatching.flush();