Pasting: Convert unknown shortcodes to Shortcode block

Blocks can specify shortcodes from which blocks should be automatically
created. For any other shortcode, the core Shortcode block will now act
as a fallback.

The main benefit of this is that, within the Shortcode block, the code
will be properly handled and never mishandled. Notably, this fixes the
case where a shortcode sitting in a Paragraph block will be picked up
with its double quotes rendered as `&doubl;`, thus breaking parsing of a
shortcode's attributes.

blocks/api/raw-handling/shortcode-converter.js

@@ -33,7 +33,7 @@ export default function( HTML ) {
 
 			const attributes = mapValues(
 				pickBy( transform.attributes, ( schema ) => schema.shortcode ),
-				( schema ) => schema.shortcode( match.shortcode.attrs ),
+				( schema ) => schema.shortcode( match.shortcode.attrs, match ),
 			);
 
 			const block = createBlock(

blocks/library/index.js

@@ -1,3 +1,4 @@
+import './shortcode';
 import './image';
 import './gallery';
 import './heading';
@@ -16,7 +17,6 @@ import './freeform';
 import './latest-posts';
 import './categories';
 import './cover-image';
-import './shortcode';
 import './text-columns';
 import './verse';
 import './video';

blocks/library/shortcode/index.js

@@ -31,6 +31,27 @@ registerBlockType( 'core/shortcode', {
 		},
 	},
 
+	transforms: {
+		from: [
+			{
+				type: 'shortcode',
+				// Per "Shortcode names should be all lowercase and use all
+				// letters, but numbers and underscores should work fine too.
+				// Be wary of using hyphens (dashes), you'll be better off not
+				// using them." in https://codex.wordpress.org/Shortcode_API
+				tag: '[A-z0-9_-]+',
+				attributes: {
+					text: {
+						type: 'string',
+						shortcode: ( attrs, { content } ) => {
+							return content;
+						},
+					},
+				},
+			},
+		],
+	},
+
 	className: false,
 
 	supportHTML: false,