fix(forward): warn when forwarding out of an encrypted room into one that is not (#330)

Forwarding from an encrypted room into an unencrypted one posts the text
(and a re-uploaded plaintext attachment) where the server can read it,
with the original author attached, and the dialog said nothing. Show a
note above Send naming the unencrypted destination(s).

Refs #330

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017PCb59uY3UKqDqt7B6hzd5

src/app/features/room/message/ForwardMessageDialog.tsx

@@ -47,8 +47,12 @@ import {
   recentForwardTargetsAtom,
   addRecentForwardTarget,
 } from '../../../state/recentForwardTargets';
-import { buildForwardContent, buildPlaintextAttachmentContent } from './forwardContent';
-import { useLocalRoomNames } from '../../../hooks/useRoomMeta';
+import {
+  buildForwardContent,
+  buildPlaintextAttachmentContent,
+  forwardEncryptionWarning,
+} from './forwardContent';
+import { useLocalRoomNames, getLocalRoomName } from '../../../hooks/useRoomMeta';
 
 type RoomRowProps = {
   room: Room;
@@ -275,6 +279,14 @@ export function ForwardMessageDialog({ mEvent, onClose }: Props) {
   // Selection persists across query changes: a room selected then filtered out
   // of the rendered slice stays selected.
   const [selectedRoomIds, setSelectedRoomIds] = useState<Set<string>>(new Set());
+  const encryptionWarning = forwardEncryptionWarning(
+    !!mx.getRoom(mEvent.getRoomId() ?? '')?.hasEncryptionStateEvent(),
+    [...selectedRoomIds]
+      .map((id) => mx.getRoom(id))
+      .filter((r): r is Room => !!r && !r.hasEncryptionStateEvent())
+      // The name the user sees (their own "Rename for me" name, if set).
+      .map((r) => getLocalRoomName(mx, r.roomId) ?? r.name),
+  );
 
   const toggleRoom = useCallback((roomId: string) => {
     setSelectedRoomIds((prev) => {
@@ -590,7 +602,13 @@ export function ForwardMessageDialog({ mEvent, onClose }: Props) {
                   shrink="No"
                   direction="Column"
                   style={{ padding: `${config.space.S200} ${config.space.S400}` }}
+                  gap="200"
                 >
+                  {encryptionWarning && (
+                    <Text size="T200" role="note" style={{ color: color.Warning.Main }}>
+                      {encryptionWarning}
+                    </Text>
+                  )}
                   <Button
                     variant="Primary"
                     size="400"

src/app/features/room/message/forwardContent.test.ts

@@ -1,7 +1,7 @@
 import { test } from 'node:test';
 import assert from 'node:assert/strict';
 import { MatrixClient, MatrixEvent } from 'matrix-js-sdk';
-import { buildForwardContent, getForwardedMeta } from './forwardContent';
+import { buildForwardContent, forwardEncryptionWarning, getForwardedMeta } from './forwardContent';
 
 // Pure content builder buildForwardContent: refuses undecryptable events, forwards
 // the latest edit (`m.new_content`), and strips reply fallbacks + `m.relates_to`.
@@ -171,3 +171,16 @@ test('getForwardedMeta rejects malformed metadata', () => {
   assert.equal(getForwardedMeta({ 'io.lotus.forwarded': { sender: 1 } }), undefined);
   assert.equal(getForwardedMeta({}), undefined);
 });
+
+test('forwardEncryptionWarning: only from an encrypted room into unencrypted ones (#330)', () => {
+  assert.equal(forwardEncryptionWarning(false, ['general']), undefined);
+  assert.equal(forwardEncryptionWarning(true, []), undefined);
+  assert.match(
+    forwardEncryptionWarning(true, ['general']) ?? '',
+    /^general isn't encrypted\..*that room, along with who originally wrote it\.$/,
+  );
+  assert.match(
+    forwardEncryptionWarning(true, ['a', 'b']) ?? '',
+    /^2 of the rooms you picked aren't encrypted\..*those rooms/,
+  );
+});

src/app/features/room/message/forwardContent.ts

@@ -122,3 +122,23 @@ export async function buildPlaintextAttachmentContent(
 
   return plainContent;
 }
+
+/**
+ * [Gitea #330] The note shown when forwarding out of an encrypted room into
+ * rooms that aren't: the text (and a re-uploaded attachment) becomes readable
+ * by the server, and the original author is shown with it. Undefined when
+ * there's nothing to warn about.
+ */
+export function forwardEncryptionWarning(
+  sourceEncrypted: boolean,
+  unencryptedDestNames: string[],
+): string | undefined {
+  if (!sourceEncrypted || unencryptedDestNames.length === 0) return undefined;
+  const where =
+    unencryptedDestNames.length === 1
+      ? `${unencryptedDestNames[0]} isn't encrypted.`
+      : `${unencryptedDestNames.length} of the rooms you picked aren't encrypted.`;
+  return `${where} The forwarded message (and any attachment) will be readable by the server and everyone in ${
+    unencryptedDestNames.length === 1 ? 'that room' : 'those rooms'
+  }, along with who originally wrote it.`;
+}