feat(dev): log the failing procedure in a tRPC batch

apps/web/src/app/api/trpc/[trpc]/route.test.ts

@@ -0,0 +1,43 @@
+import { afterEach, expect, it, jest } from '@jest/globals';
+import { initTRPC, TRPCError } from '@trpc/server';
+
+jest.mock('@/lib/trpc/init', () => ({
+  createTRPCContext: () => ({}),
+}));
+
+jest.mock('@/routers/root-router', () => {
+  const t = initTRPC.create();
+  return {
+    rootRouter: t.router({
+      ok: t.procedure.query(() => 'ok'),
+      fail: t.procedure.query(() => {
+        throw new TRPCError({
+          code: 'BAD_REQUEST',
+          message: 'SYNTHETIC_SENSITIVE_TOKEN',
+        });
+      }),
+    }),
+  };
+});
+
+afterEach(() => {
+  jest.restoreAllMocks();
+});
+
+it.each(['development', 'production', 'test'] as const)(
+  'logs only safe batch error fields in development, with NODE_ENV=%s',
+  async nodeEnv => {
+    jest.replaceProperty(process, 'env', { ...process.env, NODE_ENV: nodeEnv });
+    const log = jest.spyOn(console, 'error').mockImplementation(() => {});
+    const { GET } = await import('./route');
+
+    const response = await GET(new Request('http://localhost/api/trpc/ok,fail?batch=1'));
+
+    expect(response.status).toBe(207);
+    if (nodeEnv === 'development') {
+      expect(log.mock.calls).toEqual([['[trpc] query fail failed: BAD_REQUEST']]);
+    } else {
+      expect(log).not.toHaveBeenCalled();
+    }
+  }
+);

apps/web/src/app/api/trpc/[trpc]/route.ts

@@ -11,6 +11,16 @@ const handler = (req: Request) =>
     router: rootRouter,
     createContext: createTRPCContext,
     allowMethodOverride: true,
+    // A batched call answers 207 when one procedure fails, and folds the failure
+    // into the response body. Without this the server log shows only the 207, so
+    // nobody can tell which of a dozen batched procedures raised, or why.
+    // Development only: production reporting is unchanged.
+    onError:
+      process.env.NODE_ENV === 'development'
+        ? ({ path, type, error }) => {
+            console.error(`[trpc] ${type} ${path ?? '<no path>'} failed: ${error.code}`);
+          }
+        : undefined,
   });
 
 export { handler as GET, handler as POST };