Blocks API: Add default implementation for save setting

docs/designers-developers/developers/block-api/block-edit-save.md

@@ -226,7 +226,7 @@ For most blocks, the return value of `save` should be an [instance of WordPress
 
 _Note:_ While it is possible to return a string value from `save`, it _will be escaped_. If the string includes HTML markup, the markup will be shown on the front of the site verbatim, not as the equivalent HTML node content. If you must return raw HTML from `save`, use `wp.element.RawHTML`. As the name implies, this is prone to [cross-site scripting](https://en.wikipedia.org/wiki/Cross-site_scripting) and therefore is discouraged in favor of a WordPress Element hierarchy whenever possible.
 
-For [dynamic blocks](/docs/designers-developers/developers/tutorials/block-tutorial/creating-dynamic-blocks.md), the return value of `save` could either represent a cached copy of the block's content to be shown only in case the plugin implementing the block is ever disabled. Alternatively, return a `null` (empty) value to save no markup in post content for the dynamic block, instead deferring this to always be calculated when the block is shown on the front of the site.
+For [dynamic blocks](/docs/designers-developers/developers/tutorials/block-tutorial/creating-dynamic-blocks.md), the return value of `save` could either represent a cached copy of the block's content to be shown only in case the plugin implementing the block is ever disabled. Alternatively, you can use a built-in implementation which returns a `null` (empty) value to save no markup in post content for the dynamic block, instead deferring this to always be calculated when the block is shown on the front of the site.
 
 ### attributes
 

docs/designers-developers/developers/tutorials/block-tutorial/creating-dynamic-blocks.md

@@ -40,11 +40,6 @@ registerBlockType( 'my-plugin/latest-post', {
 			post.title.rendered
 		);
 	} ),
-
-	save: function() {
-		// Rendering in PHP
-		return null;
-	},
 } );
 ```
 {% ESNext %}
@@ -79,16 +74,11 @@ registerBlockType( 'my-plugin/latest-post', {
 			{ post.title.rendered }
 		</a>;
 	} ),
-
-	save() {
-		// Rendering in PHP
-		return null;
-	},
 } );
 ```
 {% end %}
 
-Because it is a dynamic block it also needs a server component. The rendering can be added using the `render_callback` property when using the `register_block_type` function.
+Because it is a dynamic block it doesn't need to override the default `save` implementation on the client. Instead, it needs a server component. The rendering can be added using the `render_callback` property when using the `register_block_type` function.
 
 ```php
 <?php
@@ -118,8 +108,8 @@ register_block_type( 'my-plugin/latest-post', array(
 
 There are a few things to notice:
 
-* The edit function still shows a representation of the block in the editor's context (this could be very different from the rendered version, it's up to the block's author)
-* The save function just returns null because the rendering is performed server-side.
+* The `edit` function still shows a representation of the block in the editor's context (this could be very different from the rendered version, it's up to the block's author)
+* The built-in `save` function just returns `null` because the rendering is performed server-side.
 * The server-side rendering is a function taking the block attributes and the block inner content as arguments, and returning the markup (quite similar to shortcodes)
 
 ## Live rendering in Gutenberg editor
@@ -151,11 +141,6 @@ registerBlockType( 'my-plugin/latest-post', {
 			})
 		);
 	},
-
-	save: function() {
-		// Rendering in PHP
-		return null;
-	},
 } );
 ```
 {% ESNext %}
@@ -179,11 +164,6 @@ registerBlockType( 'my-plugin/latest-post', {
 			/>
 		);
 	},
-
-	save() {
-		// Rendering in PHP
-		return null;
-	},
 } );
 ```
 {% end %}

packages/block-library/src/archives/index.js

@@ -32,9 +32,4 @@ export const settings = {
 	},
 
 	edit,
-
-	save() {
-		// Handled by PHP.
-		return null;
-	},
 };

packages/block-library/src/calendar/index.js

@@ -26,8 +26,4 @@ export const settings = {
 	},
 
 	edit,
-
-	save() {
-		return null;
-	},
 };

packages/block-library/src/categories/index.js

@@ -42,8 +42,4 @@ export const settings = {
 	},
 
 	edit,
-
-	save() {
-		return null;
-	},
 };

packages/block-library/src/latest-comments/index.js

@@ -28,8 +28,4 @@ export const settings = {
 	},
 
 	edit,
-
-	save() {
-		return null;
-	},
 };

packages/block-library/src/latest-posts/index.js

@@ -34,8 +34,4 @@ export const settings = {
 	},
 
 	edit,
-
-	save() {
-		return null;
-	},
 };

packages/block-library/src/legacy-widget/index.js

@@ -25,9 +25,4 @@ export const settings = {
 	},
 
 	edit,
-
-	save() {
-		// Handled by PHP.
-		return null;
-	},
 };

packages/block-library/src/rss/index.js

@@ -26,8 +26,4 @@ export const settings = {
 	},
 
 	edit,
-
-	save() {
-		return null;
-	},
 };

packages/block-library/src/search/index.js

@@ -22,8 +22,4 @@ export const settings = {
 	keywords: [ __( 'find' ) ],
 
 	edit,
-
-	save() {
-		return null;
-	},
 };

packages/block-library/src/tag-cloud/index.js

@@ -25,8 +25,4 @@ export const settings = {
 	},
 
 	edit,
-
-	save() {
-		return null;
-	},
 };

packages/blocks/src/api/registration.js

@@ -33,7 +33,7 @@ import { isValidIcon, normalizeIconObject } from './utils';
  * @property {?string[]}                 keywords   Additional keywords to produce
  *                                                  block as inserter search result.
  * @property {?Object}                   attributes Block attributes.
- * @property {Function}                  save       Serialize behavior of a block,
+ * @property {?Function}                 save       Serialize behavior of a block,
  *                                                  returning an element describing
  *                                                  structure of the block's post
  *                                                  content markup.
@@ -66,6 +66,7 @@ export function unstable__bootstrapServerSideBlockDefinitions( definitions ) { /
 export function registerBlockType( name, settings ) {
 	settings = {
 		name,
+		save: () => null,
 		...get( serverSideBlockDefinitions, name ),
 		...settings,
 	};

packages/blocks/src/api/test/registration.js

@@ -3,12 +3,12 @@
 /**
  * External dependencies
  */
-import { noop } from 'lodash';
+import { noop, omit } from 'lodash';
 
 /**
  * WordPress dependencies
  */
-import { addFilter, removeFilter } from '@wordpress/hooks';
+import { addFilter, removeAllFilters } from '@wordpress/hooks';
 
 /**
  * Internal dependencies
@@ -106,12 +106,6 @@ describe( 'blocks', () => {
 			expect( block ).toBeUndefined();
 		} );
 
-		it( 'should reject blocks without a save function', () => {
-			const block = registerBlockType( 'my-plugin/fancy-block-5' );
-			expect( console ).toHaveErroredWith( 'The "save" property must be specified and must be a valid function.' );
-			expect( block ).toBeUndefined();
-		} );
-
 		it( 'should reject blocks with an invalid edit function', () => {
 			const blockType = { save: noop, edit: 'not-a-function', category: 'common', title: 'block title' },
 				block = registerBlockType( 'my-plugin/fancy-block-6', blockType );
@@ -309,7 +303,7 @@ describe( 'blocks', () => {
 
 		describe( 'applyFilters', () => {
 			afterEach( () => {
-				removeFilter( 'blocks.registerBlockType', 'core/blocks/without-title' );
+				removeAllFilters( 'blocks.registerBlockType' );
 			} );
 
 			it( 'should reject valid blocks when they become invalid after executing filter', () => {
@@ -323,6 +317,15 @@ describe( 'blocks', () => {
 				expect( console ).toHaveErroredWith( 'The block "my-plugin/fancy-block-12" must have a title.' );
 				expect( block ).toBeUndefined();
 			} );
+
+			it( 'should reject valid blocks when they become invalid after executing filter which removes save property', () => {
+				addFilter( 'blocks.registerBlockType', 'core/blocks/without-save', ( settings ) => {
+					return omit( settings, 'save' );
+				} );
+				const block = registerBlockType( 'my-plugin/fancy-block-13', defaultBlockSettings );
+				expect( console ).toHaveErroredWith( 'The "save" property must be specified and must be a valid function.' );
+				expect( block ).toBeUndefined();
+			} );
 		} );
 	} );