Don't ignore errors when initializing the nativeFS (pyodide#5434)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

docs/project/changelog.md

@@ -19,6 +19,7 @@ myst:
 _Insert Date Here_
 
 - Added the `context` parameter to `WebLoop.create_task()` {pr}`5431`
+- {{ Fix }} `mountNativeFS` API now correctly propagates the error. {pr}`5434`
 
 ### Packages
 

src/js/api.ts

@@ -18,6 +18,7 @@ import {
   syncUpSnapshotLoad1,
   syncUpSnapshotLoad2,
 } from "./snapshot";
+import { syncLocalToRemote, syncRemoteToLocal } from "./nativefs";
 
 // Exported for micropip
 API.loadBinaryFile = loadBinaryFile;
@@ -556,12 +557,11 @@ export class PyodideAPI {
     );
 
     // sync native ==> browser
-    await new Promise((resolve, _) => Module.FS.syncfs(true, resolve));
+    await syncRemoteToLocal(Module);
 
     return {
       // sync browser ==> native
-      syncfs: async () =>
-        new Promise((resolve, _) => Module.FS.syncfs(false, resolve)),
+      syncfs: async () => await syncLocalToRemote(Module),
     };
   }
 

src/js/nativefs.ts

@@ -1,5 +1,34 @@
 import { Module } from "./types";
 
+/**
+ * @private
+ */
+async function syncfs(m: Module, direction: boolean): Promise<void> {
+  return new Promise((resolve, reject) => {
+    m.FS.syncfs(direction, (err: any) => {
+      if (err) {
+        reject(err);
+      } else {
+        resolve();
+      }
+    });
+  });
+}
+
+/**
+ * @private
+ */
+export async function syncLocalToRemote(m: Module): Promise<void> {
+  return await syncfs(m, false);
+}
+
+/**
+ * @private
+ */
+export async function syncRemoteToLocal(m: Module): Promise<void> {
+  return await syncfs(m, true);
+}
+
 /**
  * @private
  */