fix: surface error when wallet is on an unsupported chain in SignIn

.changeset/fix-sign-in-silent-bail-unsupported-chain.md

@@ -0,0 +1,5 @@
+---
+"@rainbow-me/rainbowkit": patch
+---
+
+Show an error in the Sign In screen when the wallet is connected on a chain that is not in the configured chains list. Previously the Sign Message button would silently do nothing in this case, leaving the user stuck with no feedback.

packages/rainbowkit/src/components/SignIn/SignIn.test.tsx

@@ -142,4 +142,31 @@ describe('SignIn', () => {
 
     expect(createMessage).toHaveBeenCalledTimes(2);
   });
+
+  it('shows an error message when the wallet is on an unsupported chain', async () => {
+    wagmiMocks.useAccount.mockReturnValue({
+      address,
+      chain: undefined,
+    });
+    const createMessage = vi.fn(() => 'message');
+    wagmiMocks.signMessageAsync.mockReturnValue(new Promise(() => {}));
+
+    renderSignIn({ createMessage });
+
+    const button = await screen.findByTestId('rk-auth-message-button');
+    await waitFor(() => expect(button).toHaveTextContent('Sign message'));
+
+    fireEvent.click(button);
+
+    await waitFor(() =>
+      expect(
+        screen.getByText(
+          'Your wallet is on an unsupported network. Switch to a supported network and try again.',
+        ),
+      ).toBeInTheDocument(),
+    );
+    expect(createMessage).not.toHaveBeenCalled();
+    expect(wagmiMocks.signMessageAsync).not.toHaveBeenCalled();
+    expect(button).toHaveTextContent('Sign message');
+  });
 });

packages/rainbowkit/src/components/SignIn/SignIn.tsx

@@ -62,10 +62,21 @@ export function SignIn({
       const chainId = activeChain?.id;
       const { nonce } = state;
 
-      if (!address || !chainId || !nonce) {
+      if (!address || !nonce) {
         return;
       }
 
+      if (!chainId) {
+        // The wallet is connected on a chain that is not in the
+        // configured chains list, so wagmi reports chain as undefined.
+        // Surface an actionable error rather than bailing silently.
+        return setState((x) => ({
+          ...x,
+          errorMessage: i18n.t('sign_in.signature.unsupported_chain_error'),
+          status: 'idle',
+        }));
+      }
+
       setState((x) => ({
         ...x,
         errorMessage: undefined,

packages/rainbowkit/src/locales/en_US.json

@@ -39,7 +39,8 @@
       "verifying": "Verifying signature...",
       "signing_error": "Error signing message, please retry!",
       "verifying_error": "Error verifying signature, please retry!",
-      "oops_error": "Oops, something went wrong!"
+      "oops_error": "Oops, something went wrong!",
+      "unsupported_chain_error": "Your wallet is on an unsupported network. Switch to a supported network and try again."
     }
   },