Handle error identifying hex from MakeCode. (#1043)

Ensure we show the original error (suboptimal though it may well be)
rather than silently failing.

Author: microbit-matt-hillsdon

src/e2e/open.test.ts

@@ -29,6 +29,19 @@ describe("Browser - open", () => {
     await app.findProjectName("Untitled project");
   });
 
+  it("Correctly handles a hex that's actually Python", async () => {
+    await app.loadFiles("testData/not-a-hex.hex", {
+      acceptDialog: LoadDialogType.NONE,
+    });
+
+    await app.findAlertText(
+      "Cannot load file",
+      // Would be great to have custom messages here but needs error codes
+      // pushing into microbit-fs.
+      "Malformed .hex file, could not parse any registers"
+    );
+  });
+
   it("Loads a v1.0.1 hex file", async () => {
     await app.loadFiles("testData/1.0.1.hex");
 

src/project/project-actions.tsx

@@ -5,7 +5,7 @@
  */
 import { Link, List, ListItem, Stack } from "@chakra-ui/layout";
 import { Text, VStack } from "@chakra-ui/react";
-import { isMakeCodeForV1Hex } from "@microbit/microbit-universal-hex";
+import { isMakeCodeForV1Hex as isMakeCodeForV1HexNoErrorHandling } from "@microbit/microbit-universal-hex";
 import { saveAs } from "file-saver";
 import { ReactNode } from "react";
 import { FormattedMessage, IntlShape } from "react-intl";
@@ -1029,6 +1029,16 @@ export class ProjectActions {
   };
 }
 
+const isMakeCodeForV1Hex = (hexStr: string) => {
+  try {
+    return isMakeCodeForV1HexNoErrorHandling(hexStr);
+  } catch (e) {
+    // We just use this to give a better message in error scenarios so we don't
+    // care if we failed to parse it etc.
+    return false;
+  }
+};
+
 export const defaultedProject = (
   fs: FileSystem,
   intl: IntlShape

testData/not-a-hex.hex

@@ -0,0 +1,6 @@
+# Add your Python code here. E.g.
+from microbit import *
+
+
+while True:
+    display.scroll('Hello from main.py!')