Build: Switch from UglifyJS to SWC minify, make the minified file ES5

More recent UglifyJS versions have started converting regular functions to arrow
ones, making ES5 source file migrated to a ES2015+ minified one. We want to
avoid that even in 1.14.x as long as we keep the source file in ES5.

Ref mishoo/UglifyJS#5967
Ref jquery/download.jqueryui.com#629

Gruntfile.js

@@ -51,9 +51,6 @@ const cssFiles = [
 
 // minified files
 const minify = {
-	options: {
-		preserveComments: false
-	},
 	main: {
 		options: {
 			banner: createBanner( uiFiles )
@@ -174,7 +171,7 @@ grunt.initConfig( {
 		}
 	},
 
-	uglify: minify,
+	minify,
 	htmllint: {
 		good: {
 			options: {
@@ -403,9 +400,9 @@ grunt.registerTask( "lint", [
 	"csslint",
 	"htmllint"
 ] );
-grunt.registerTask( "build", [ "requirejs", "concat" ] );
+grunt.registerTask( "build", [ "requirejs", "concat", "minify:main" ] );
 grunt.registerTask( "default", [ "lint", "build" ] );
-grunt.registerTask( "sizer", [ "requirejs:js", "uglify:main", "compare_size:all" ] );
-grunt.registerTask( "sizer_all", [ "requirejs:js", "uglify", "compare_size" ] );
+grunt.registerTask( "sizer", [ "requirejs:js", "minify:main", "compare_size:all" ] );
+grunt.registerTask( "sizer_all", [ "requirejs:js", "minify", "compare_size" ] );
 
 };

build/tasks/minify.js

@@ -0,0 +1,53 @@
+"use strict";
+
+const swc = require( "@swc/core" );
+
+module.exports = function( grunt ) {
+
+grunt.registerMultiTask( "minify", async function() {
+	const done = this.async();
+	const options = this.options();
+
+	for ( const file of this.files ) {
+		if ( file.src.length === 0 ) {
+			grunt.log.writeln(
+				`No source file found, skipping minification to "${ file.dest }".` );
+			continue;
+		}
+		if ( file.src.length !== 1 ) {
+			grunt.fail.warn( "Minifying multiple source files into one " +
+				"destination file not supported" );
+		}
+
+		const contents = grunt.file.read( file.src[ 0 ] );
+
+		const { code } = await swc.minify(
+			contents,
+			{
+				compress: {
+					ecma: 5,
+					hoist_funs: false,
+					loops: false
+				},
+				format: {
+					ecma: 5,
+					asciiOnly: true,
+					comments: false,
+					preamble: options.banner
+				},
+				inlineSourcesContent: false,
+				mangle: true,
+				module: false,
+				sourceMap: false
+			}
+		);
+
+		grunt.file.write( file.dest, code );
+
+		grunt.log.writeln( `File ${ file.dest } created.` );
+	}
+
+	done();
+} );
+
+};

package.json

@@ -55,6 +55,7 @@
 		"jquery": ">=1.12.0 <5.0.0"
 	},
 	"devDependencies": {
+		"@swc/core": "1.11.5",
 		"commitplease": "3.2.0",
 		"eslint-config-jquery": "3.0.2",
 		"grunt": "1.6.1",
@@ -63,7 +64,6 @@
 		"grunt-contrib-concat": "2.1.0",
 		"grunt-contrib-csslint": "2.0.0",
 		"grunt-contrib-requirejs": "1.0.0",
-		"grunt-contrib-uglify": "5.2.2",
 		"grunt-eslint": "24.0.1",
 		"grunt-git-authors": "3.2.0",
 		"grunt-html": "17.1.0",