Fix isIncluded error when using rollup-plugin-typescript2 (#4725)

* Wait for this.load before closing bundle

* Support this.load after build without awaiting it

* Do not await this.load in build as that would be the job of the plugin

src/Module.ts

@@ -685,8 +685,12 @@ export default class Module {
 		this.includeAllExports(false);
 	}
 
-	isIncluded(): boolean {
-		return this.ast!.included || this.namespace.included || this.importedFromNotTreeshaken;
+	isIncluded(): boolean | null {
+		// Modules where this.ast is missing have been loaded via this.load and are
+		// not yet fully processed, hence they cannot be included.
+		return (
+			this.ast && (this.ast.included || this.namespace.included || this.importedFromNotTreeshaken)
+		);
 	}
 
 	linkImports(): void {

test/function/samples/preload-after-build/_config.js

@@ -0,0 +1,23 @@
+const path = require('node:path');
+
+module.exports = {
+	description: 'supports this.load() in buildEnd and renderStart',
+	options: {
+		plugins: [
+			{
+				name: 'test',
+				buildEnd() {
+					this.load({ id: path.join(__dirname, 'other2.js') });
+				},
+				moduleParsed({ id }) {
+					if (id.endsWith('main.js')) {
+						this.load({ id: path.join(__dirname, 'other1.js') });
+					}
+				},
+				renderStart() {
+					this.load({ id: path.join(__dirname, 'other3.js') });
+				}
+			}
+		]
+	}
+};

test/function/samples/preload-after-build/main.js

@@ -0,0 +1 @@
+assert.ok(true);

test/function/samples/preload-after-build/other1.js

@@ -0,0 +1 @@
+assert.ok(true);

test/function/samples/preload-after-build/other2.js

@@ -0,0 +1 @@
+assert.ok(true);

test/function/samples/preload-after-build/other3.js

@@ -0,0 +1 @@
+assert.ok(true);