docgen: replace espree with babel. (#21853)

packages/docgen/README.md

@@ -38,6 +38,12 @@ This command will generate a file named `entry-point-api.md` containing all the
 * **--use-token** `(String)`: This options allows you to customize the string between the tokens. For example, `--use-token my-api` will look up for the start token <code>&lt;!-- START TOKEN(my-api) --&gt;</code> and the end token <code>&lt;!-- END TOKEN(my-api) --&gt;</code>. Depends on `--to-token`.
 * **--debug**: Run in debug mode, which outputs some intermediate files useful for debugging.
 
+### Babel Configuration
+
+`@wordpress/docgen` follows the default [project-wide configuration of Babel](https://babeljs.io/docs/en/next/config-files#project-wide-configuration). Like Babel, it will automatically search for a `babel.config.json` file, or an equivalent one using the [supported extensions](https://babeljs.io/docs/en/next/config-files#supported-file-extensions), in the project root directory.
+
+Without it, `@wordpress/docgen` runs with the default option. In other words, it cannot parse JSX or other advanced syntaxes.
+
 ## Examples
 
 ### Default export

packages/docgen/package.json

@@ -22,8 +22,8 @@
 		"docgen": "./bin/cli.js"
 	},
 	"dependencies": {
+		"@babel/core": "^7.9.0",
 		"doctrine": "^2.1.0",
-		"espree": "^4.0.0",
 		"lodash": "^4.17.15",
 		"mdast-util-inject": "1.1.0",
 		"optionator": "0.8.2",

packages/docgen/src/engine.js

@@ -1,24 +1,17 @@
 /**
  * External dependencies.
  */
-const espree = require( 'espree' );
+const babel = require( '@babel/core' );
 const { flatten } = require( 'lodash' );
 
 /**
  * Internal dependencies.
  */
 const getIntermediateRepresentation = require( './get-intermediate-representation' );
 
-const getAST = ( source ) =>
-	espree.parse( source, {
-		attachComment: true,
-		loc: true,
-		ecmaVersion: 2018,
-		ecmaFeatures: {
-			jsx: true,
-		},
-		sourceType: 'module',
-	} );
+const getAST = ( source ) => {
+	return babel.parse( source || '' ).program;
+};
 
 const getExportTokens = ( ast ) =>
 	ast.body.filter( ( node ) =>