feat: handle python input synchronously (#52526)

Co-authored-by: Shaun Hamilton <shauhami020@gmail.com>

tools/client-plugins/browser-scripts/python-worker.ts

@@ -0,0 +1,81 @@
+// We have to specify pyodide.js because we need to import that file (not .mjs)
+// and 'import' defaults to .mjs
+import { loadPyodide, type PyodideInterface } from 'pyodide/pyodide.js';
+import pkg from 'pyodide/package.json';
+
+const ctx: Worker & typeof globalThis = self as unknown as Worker &
+  typeof globalThis;
+
+let pyodide: PyodideInterface;
+
+interface PythonRunEvent extends MessageEvent {
+  data: {
+    code: {
+      contents: string;
+      editableContents: string;
+      original: { [id: string]: string };
+    };
+  };
+}
+
+async function setupPyodide() {
+  if (pyodide) return pyodide;
+
+  pyodide = await loadPyodide({
+    // TODO: host this ourselves
+    indexURL: `https://cdn.jsdelivr.net/pyodide/v${pkg.version}/full/`
+  });
+
+  // We freeze this to prevent learners from getting the worker into a
+  // weird state. NOTE: this has to come after pyodide is loaded, because
+  // pyodide modifies self while loading.
+  Object.freeze(self);
+
+  // eslint-disable-next-line @typescript-eslint/no-unsafe-call
+  const str = pyodide.globals.get('str') as (x: unknown) => string;
+
+  function print(...args: unknown[]) {
+    const text = args.map(x => str(x)).join(' ');
+    postMessage({ type: 'print', text });
+  }
+
+  function input(text: string) {
+    // TODO: send unique ids to the main thread and the service worker, so we
+    // can have multiple concurrent input requests.
+    postMessage({ type: 'input', text });
+    const request = new XMLHttpRequest();
+    request.open('POST', '/python/intercept-input/', false);
+    request.send(null);
+
+    return request.responseText;
+  }
+
+  // I tried setting jsglobals here, to provide 'input' and 'print' to python,
+  // without having to modify the global window object. However, it didn't work
+  // because pyodide needs access to that object. Instead, I used
+  // registerJsModule when setting up runPython.
+
+  // Make print available to python
+  pyodide.registerJsModule('jscustom', {
+    print,
+    input
+  });
+  // TODO: use a fresh global object for each runPython call if we stop terminating
+  // the worker when the user input changes. (See python-test-evaluator.ts)
+  pyodide.runPython(`
+  import jscustom
+  from jscustom import print
+  from jscustom import input
+`);
+
+  return pyodide;
+}
+
+void setupPyodide();
+
+ctx.onmessage = async (e: PythonRunEvent) => {
+  const code = (e.data.code.contents || '').slice();
+  const pyodide = await setupPyodide();
+  // use pyodide.runPythonAsync if we want top-level await
+  pyodide.runPython(code);
+};