feat(boot): support loading ESM artifacts

BREAKING CHANGE: `loadClassesFromFiles` now returns a `Promise`

see: #10744
Signed-off-by: Rifa Achrinza <25147899+achrinza@users.noreply.github.com>

Author: achrinza

packages/boot/src/__tests__/fixtures/cjs.artifact.cjs

@@ -0,0 +1 @@
+export class DummyCJSClass {}

packages/boot/src/__tests__/fixtures/esm.artifact.mjs

@@ -0,0 +1 @@
+export class DummyESMClass {}

packages/boot/src/__tests__/unit/booters/booter-utils.unit.ts

@@ -66,7 +66,37 @@ describe('booter-utils unit tests', () => {
       const files = [resolve(sandbox.path, 'multiple.artifact.js')];
       const NUM_CLASSES = 2; // Number of classes in above file
 
-      const classes = loadClassesFromFiles(files, sandbox.path);
+      const classes = await loadClassesFromFiles(files, sandbox.path);
+      expect(classes).to.have.lengthOf(NUM_CLASSES);
+      expect(classes[0]).to.be.a.Function();
+      expect(classes[1]).to.be.a.Function();
+    });
+
+    it('loads classes from CJS files', async () => {
+      const artifactFilename = 'multiple.artifact.cjs';
+      await sandbox.copyFile(
+        resolve(__dirname, '../../fixtures/multiple.artifact.cjs'),
+      );
+      const NUM_CLASSES = 2;
+      const classes = await loadClassesFromFiles(
+        [resolve(sandbox.path, artifactFilename)],
+        sandbox.path,
+      );
+      expect(classes).to.have.lengthOf(NUM_CLASSES);
+      expect(classes[0]).to.be.a.Function();
+      expect(classes[1]).to.be.a.Function();
+    });
+
+    it('loads classes from ESM files', async () => {
+      const artifactFilename = 'multiple.artifact.mjs';
+      await sandbox.copyFile(
+        resolve(__dirname, '../../fixtures/multiple.artifact.mjs'),
+      );
+      const NUM_CLASSES = 2;
+      const classes = await loadClassesFromFiles(
+        [resolve(sandbox.path, artifactFilename)],
+        sandbox.path,
+      );
       expect(classes).to.have.lengthOf(NUM_CLASSES);
       expect(classes[0]).to.be.a.Function();
       expect(classes[1]).to.be.a.Function();
@@ -78,16 +108,16 @@ describe('booter-utils unit tests', () => {
       );
       const files = [resolve(sandbox.path, 'empty.artifact.js')];
 
-      const classes = loadClassesFromFiles(files, sandbox.path);
+      const classes = await loadClassesFromFiles(files, sandbox.path);
       expect(classes).to.be.an.Array();
       expect(classes).to.be.empty();
     });
 
     it('throws an error given a non-existent file', async () => {
       const files = [resolve(sandbox.path, 'fake.artifact.js')];
-      expect(() => loadClassesFromFiles(files, sandbox.path)).to.throw(
-        /Cannot find module/,
-      );
+      await expect(
+        loadClassesFromFiles(files, sandbox.path),
+      ).to.be.rejectedWith(/Cannot find module/);
     });
   });
 });

packages/boot/src/booters/base-artifact.booter.ts

@@ -137,6 +137,9 @@ export class BaseArtifactBooter implements Booter {
    * and then process the artifact classes as appropriate.
    */
   async load() {
-    this.classes = loadClassesFromFiles(this.discovered, this.projectRoot);
+    this.classes = await loadClassesFromFiles(
+      this.discovered,
+      this.projectRoot,
+    );
   }
 }

packages/boot/src/booters/booter-utils.ts

@@ -46,14 +46,14 @@ export function isClass(target: any): target is Constructor<any> {
  * @param projectRootDir - The project root directory
  * @returns An array of Class constructors from a file
  */
-export function loadClassesFromFiles(
+export async function loadClassesFromFiles(
   files: string[],
   projectRootDir: string,
-): Constructor<{}>[] {
+): Promise<Constructor<{}>[]> {
   const classes: Constructor<{}>[] = [];
   for (const file of files) {
     debug('Loading artifact file %j', path.relative(projectRootDir, file));
-    const moduleObj = require(file);
+    const moduleObj = await import(file);
     for (const k in moduleObj) {
       const exported = moduleObj[k];
       if (isClass(exported)) {