widgets: Make Zod schema for widget extra data stricter and extendable.

The schema now ensures extra data is validated according to the widget
type. This also makes it easier to modify the extra data for any widget
or add new widget types in the future.

web/src/submessage.ts

@@ -7,32 +7,35 @@ import type {Message} from "./message_store";
 import type {Submessage} from "./types";
 import * as widgetize from "./widgetize";
 
-export const zform_widget_extra_data_schema = z.object({
-    choices: z.array(
-        z.object({
-            type: z.string(),
-            long_name: z.string(),
-            reply: z.string(),
-            short_name: z.string(),
-        }),
-    ),
-    heading: z.string(),
-    type: z.literal("choices"),
-});
-
-const poll_widget_extra_data_schema = z.object({
-    question: z.string().optional(),
-    options: z.array(z.string()).optional(),
-});
+export const zform_widget_extra_data_schema = z
+    .object({
+        choices: z.array(
+            z.object({
+                type: z.string(),
+                long_name: z.string(),
+                reply: z.string(),
+                short_name: z.string(),
+            }),
+        ),
+        heading: z.string(),
+        type: z.literal("choices"),
+    })
+    .nullable();
+
+const poll_widget_extra_data_schema = z
+    .object({
+        question: z.string().optional(),
+        options: z.array(z.string()).optional(),
+    })
+    .nullable();
 
 const widget_data_event_schema = z.object({
     sender_id: z.number(),
-    data: z.object({
-        widget_type: z.string().optional(),
-        extra_data: z
-            .union([zform_widget_extra_data_schema, poll_widget_extra_data_schema])
-            .nullable(),
-    }),
+    data: z.discriminatedUnion("widget_type", [
+        z.object({widget_type: z.literal("poll"), extra_data: poll_widget_extra_data_schema}),
+        z.object({widget_type: z.literal("zform"), extra_data: zform_widget_extra_data_schema}),
+        z.object({widget_type: z.literal("todo"), extra_data: z.null()}),
+    ]),
 });
 
 const inbound_data_event_schema = z.object({