fix allDeps list

lib/ContextModule.js

@@ -1104,9 +1104,13 @@ module.exports = webpackEmptyAsyncContext;`;
 			)
 		);
 		const set = new Set();
-		const allDeps = /** @type {ContextElementDependency[]} */ (
-			this.dependencies.concat(this.blocks.map(b => b.dependencies[0]))
-		);
+		const allDeps =
+			this.dependencies.length > 0
+				? /** @type {ContextElementDependency[]} */ (this.dependencies).slice()
+				: [];
+		for (const block of this.blocks)
+			for (const dep of block.dependencies)
+				allDeps.push(/** @type {ContextElementDependency} */ (dep));
 		set.add(RuntimeGlobals.module);
 		set.add(RuntimeGlobals.hasOwnProperty);
 		if (allDeps.length > 0) {

test/cases/runtime/issue-15518/dynamic_a/module_a1.js

@@ -0,0 +1,5 @@
+
+let printLog = () => console.log("module_a1");
+
+export const log = printLog;
+

test/cases/runtime/issue-15518/dynamic_a/module_a2.js

@@ -0,0 +1,3 @@
+let printLog = async () => {
+    console.log("module_a2");
+};

test/cases/runtime/issue-15518/index.js

@@ -0,0 +1,13 @@
+async function dynamic_import(dir, name) {
+	if (dir === "a") {
+		return import(
+			/* webpackChunkName: "a" */
+			/* webpackMode: "lazy-once" */
+			`./dynamic_a/${name}.js`);
+	}
+	throw new Error(`${dir} directory not found`);
+}
+
+it("should compile and run", async () => {
+	await dynamic_import("a", "module_a1");
+});