From b1565444ab8a480b510a2f9dcd03975459ce0289 Mon Sep 17 00:00:00 2001
From: Matt Hillsdon <matt.hillsdon@microbit.org>
Date: Wed, 11 Nov 2026 12:32:40 +0000
Subject: [PATCH] Use simulator 0.2 and add simDebugWasm flag

The flag passes debugWasm through to the simulator iframe so it loads
its debug firmware, which enables Emscripten assertions and has DWARF
for the DevTools C/C++ debugging extension.
---
 src/flags.ts                | 8 ++++++++
 src/simulator/Simulator.tsx | 6 +++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/src/flags.ts b/src/flags.ts
index 55b1e344c..20a4a9073 100644
--- a/src/flags.ts
+++ b/src/flags.ts
@@ -49,6 +49,13 @@ export type Flag =
    * Injects the webmanifest which allows installation.
    */
   | "pwa"
+  /**
+   * Passes the debugWasm flag to the simulator.
+   *
+   * The simulator then loads its debug firmware, which enables Emscripten
+   * assertions and has DWARF for the DevTools C/C++ debugging extension.
+   */
+  | "simDebugWasm"
   /**
    * Enables in-context Crowdin translating.
    */
@@ -71,6 +78,7 @@ const allFlags: FlagMetadata[] = [
     name: "pwa",
     defaultOnStages: ["REVIEW", "STAGING", "PRODUCTION"],
   },
+  { name: "simDebugWasm", defaultOnStages: [] },
 ];
 
 type Flags = Record<Flag, boolean>;
diff --git a/src/simulator/Simulator.tsx b/src/simulator/Simulator.tsx
index 7c9b5b7eb..0f197d7eb 100644
--- a/src/simulator/Simulator.tsx
+++ b/src/simulator/Simulator.tsx
@@ -17,6 +17,7 @@ import SimulatorActionBar from "./SimulatorActionBar";
 import SimulatorSplitView from "./SimulatorSplitView";
 import SimSerialTabControlProvider from "./tab-control-hooks";
 import { stage } from "../environment";
+import { flags } from "../flags";
 
 export enum RunningStatus {
   RUNNING,
@@ -41,7 +42,7 @@ const Simulator = ({
   const brand500 = token("colors.brand.500");
   const url = useMemo(() => {
     const production =
-      "https://python-simulator.usermbit.org/v/0.1/simulator.html?flag=sw";
+      "https://python-simulator.usermbit.org/v/0.2/simulator.html?flag=sw";
     const staging =
       "https://python-simulator.usermbit.org/staging/simulator.html?flag=sw";
 
@@ -50,6 +51,9 @@ const Simulator = ({
     //const url = new URL(`https://review-python-simulator.usermbit.org/${branch}/simulator.html`);
     const url = new URL(stage === "PRODUCTION" ? production : staging);
     url.searchParams.append("color", brand500);
+    if (flags.simDebugWasm) {
+      url.searchParams.append("flag", "debugWasm");
+    }
     return url.toString();
   }, [brand500]);