msglist: Handle topic permalinks (/with/<id>) just as we do /near/ links

Explanation in a comment, which quotes Greg in zulip#5866.

Fixes: zulip#5866

src/message/__tests__/messageActions-test.js

@@ -68,6 +68,21 @@ describe('messageActions', () => {
         pmNarrowFromUsersUnsafe([user1, user2]),
       );
     });
+
+    test('handles /with/ links', async () => {
+      const stream = eg.makeStream({ stream_id: 1, name: 'test' });
+      const user1 = eg.makeUser({ user_id: 1, full_name: 'user 1' });
+      const user2 = eg.makeUser({ user_id: 2, full_name: 'user 2' });
+      const { store } = prepare({ streams: [stream], users: [user1, user2] });
+
+      await checkLink(store, '#narrow/stream/1-test/topic/hello/with/1', topicNarrow(1, 'hello'));
+      await checkLink(store, '#narrow/dm/1-user-1/with/1', pmNarrowFromUsersUnsafe([user1]));
+      await checkLink(
+        store,
+        '#narrow/dm/1,2-group/with/1',
+        pmNarrowFromUsersUnsafe([user1, user2]),
+      );
+    });
   });
 
   describe('doNarrow', () => {

src/utils/internalLinks.js

@@ -146,7 +146,7 @@ export const getNarrowFromNarrowLink = (
   if (
     // 'dm' is new in server-7.0; means the same as 'pm-with'
     (hashSegments.length === 2
-      // probably a /near/ link
+      // probably a /near/ or /with/ link
       || hashSegments.length === 4)
     && (hashSegments[0] === 'pm-with' || hashSegments[0] === 'dm')
   ) {
@@ -161,7 +161,7 @@ export const getNarrowFromNarrowLink = (
 
   if (
     (hashSegments.length === 4
-      // probably a /near/ link
+      // probably a /near/ or /with/ link
       || hashSegments.length === 6)
     // 'channel' is new in server-9.0; means the same as 'stream'
     && (hashSegments[0] === 'stream' || hashSegments[0] === 'channel')
@@ -217,9 +217,18 @@ export const getNearOperandFromLink = (url: URL, realm: URL): number | null => {
     (str, i) =>
       // This is a segment where we expect an operator to be specified.
       i % 2 === 0
-      // The operator is 'near' and its meaning is not negated (`str` does
-      // not start with "-").
-      && str === 'near',
+      // The operator is 'near' or 'with' and its meaning is not negated
+      // (`str` does not start with "-").
+      //
+      // Quoting Greg from #5866:
+      // > Currently the app doesn't interpret the "anchor" meaning of
+      // > `/near/` links at all (that's #3604) — we already effectively
+      // > give `/near/` links exactly the meaning that the upcoming
+      // > `/with/` links will have. So to handle the new links, we just
+      // > need to parse them and then handle them the way we already handle
+      // > `/near/` links.
+      // Which makes sense for this legacy codebase.
+      && (str === 'near' || str === 'with'),
   );
   if (nearOperatorIndex < 0) {
     return null;