Build: Auto-convert sources to AMD

jQuery source has been migrated in gh-4541 from AMD to ES modules. To maintain
support for consumers of our AMD modules, this commits adds a task transpiling
the ES modules sources in `src/` to AMD in `amd/`.

A "Load with AMD" checkbox was also restored to the QUnit setup. Note that,
contrary to jQuery 3.x, AMD files need to be generated via `grunt amd` or
`grunt` as sources are not authored in ECMAScript modules. To achieve a similar
no-compile experience during jQuery 4.x testing, use the new "Load as modules"
checkbox which works in all supported browsers except for IE & Edge (the
legacy, EdgeHTML-based one).

Ref gh-4541
Closes gh-4554

1 files changed, 43 insertions, 0 deletions

diff --git a/build/tasks/amd.js b/build/tasks/amd.js
new file mode 100644
index 000000000..617773ff2
--- /dev/null
+++ b/build/tasks/amd.js
@@ -0,0 +1,43 @@
+/**
+ * Compiles sources from ES Modules in `src/` to AMD in `amd/`.
+ */
+
+"use strict";
+
+module.exports = function( grunt ) {
+	const path = require( "path" );
+	const rimraf = require( "rimraf" );
+	const rollup = require( "rollup" );
+	const srcFolder = path.resolve( __dirname, "..", "..", "src" );
+	const amdFolder = path.resolve( srcFolder, "..", "amd" );
+	const inputFileName = "jquery.js";
+
+	const inputRollupOptions = {
+		input: path.resolve( srcFolder, inputFileName ),
+		preserveModules: true
+	};
+
+	const outputRollupOptions = {
+		format: "amd",
+		dir: "amd"
+	};
+
+	grunt.registerTask(
+		"amd",
+		"Convert ES modules from `src/` to AMD modules in `amd/`",
+		async function() {
+			const done = this.async();
+
+			try {
+				grunt.verbose.writeln( "Removing the 'amd' directory..." );
+				rimraf( amdFolder, async function() {
+					const bundle = await rollup.rollup( inputRollupOptions );
+					await bundle.write( outputRollupOptions );
+					grunt.log.ok( "Sources from 'src' converted to AMD in 'amd'." );
+					done();
+				} );
+			} catch ( err ) {
+				done( err );
+			}
+		} );
+};