narrow: Add 'more topics' state to browser history.

When navigating "back" or "forward", the left sidebar state
should be restored.

Earlier, "more topics" expanded was not considered a distinct
state.

This commit makes it possible to correctly place you in the
"more topics" view or not, depending on where you were.

Fixes #29548.

web/src/browser_history.ts

@@ -154,3 +154,21 @@ export function set_hash(hash: string): void {
         window.location.hash = hash;
     }
 }
+
+type StateData = {
+    narrow_pointer?: number;
+    narrow_offset?: number;
+    show_more_topics?: boolean;
+};
+
+export function update_current_history_state_data(new_data: StateData): void {
+    // eslint-disable-next-line @typescript-eslint/consistent-type-assertions
+    const current_state = history.state as StateData | null;
+    const current_state_data = {
+        narrow_pointer: current_state?.narrow_pointer,
+        narrow_offset: current_state?.narrow_offset,
+        show_more_topics: current_state?.show_more_topics,
+    };
+    const state_data = {...current_state_data, ...new_data};
+    history.replaceState(state_data, "", window.location.href);
+}

web/src/hashchange.js

@@ -182,6 +182,7 @@ function do_hashchange_normal(from_reload) {
             const narrow_opts = {
                 change_hash: false, // already set
                 trigger: "hash change",
+                show_more_topics: false,
             };
             if (from_reload) {
                 blueslip.debug("We are narrowing as part of a reload.");
@@ -191,10 +192,11 @@ function do_hashchange_normal(from_reload) {
                 }
             }
 
-            const location_data_for_hash = history.state;
+            const data_for_hash = history.state;
-            if (location_data_for_hash) {
+            if (data_for_hash) {
-                narrow_opts.then_select_id = location_data_for_hash.narrow_pointer;
+                narrow_opts.then_select_id = data_for_hash.narrow_pointer;
-                narrow_opts.then_select_offset = location_data_for_hash.narrow_offset;
+                narrow_opts.then_select_offset = data_for_hash.narrow_offset;
+                narrow_opts.show_more_topics = data_for_hash.show_more_topics ?? false;
             }
             narrow.activate(terms, narrow_opts);
             return true;

web/src/narrow.js

@@ -92,6 +92,10 @@ export function update_hash_to_match_filter(filter, trigger) {
     }
     const new_hash = hash_util.search_terms_to_hash(filter.terms());
     changehash(new_hash, trigger);
+
+    if (stream_list.is_zoomed_in()) {
+        browser_history.update_current_history_state_data({show_more_topics: true});
+    }
 }
 
 function create_and_update_message_list(filter, id_info, opts) {
@@ -166,6 +170,7 @@ function create_and_update_message_list(filter, id_info, opts) {
     // workflow we have which calls `narrow.activate` after hash is updated.
     if (opts.change_hash) {
         update_hash_to_match_filter(filter, opts.trigger);
+        opts.show_more_topics = history.state?.show_more_topics ?? false;
     }
 
     // Show the new set of messages. It is important to set message_lists.current to
@@ -263,6 +268,7 @@ export function activate(raw_terms, opts) {
         then_select_offset: undefined,
         change_hash: true,
         trigger: "unknown",
+        show_more_topics: false,
         ...opts,
     };
 
@@ -606,7 +612,7 @@ export function activate(raw_terms, opts) {
             });
         }
 
-        handle_post_view_change(msg_list);
+        handle_post_view_change(msg_list, opts);
 
         unread_ui.update_unread_banner();
 
@@ -1086,7 +1092,7 @@ export function to_compose_target() {
     }
 }
 
-function handle_post_view_change(msg_list) {
+function handle_post_view_change(msg_list, opts) {
     const filter = msg_list.data.filter;
     scheduled_messages_feed_ui.update_schedule_message_indicator();
     typing_events.render_notifications_for_narrow();
@@ -1103,7 +1109,7 @@ function handle_post_view_change(msg_list) {
     message_view_header.render_title_area();
     narrow_title.update_narrow_title(filter);
     left_sidebar_navigation_area.handle_narrow_activated(filter);
-    stream_list.handle_narrow_activated(filter);
+    stream_list.handle_narrow_activated(filter, opts.change_hash, opts.show_more_topics);
     pm_list.handle_narrow_activated(filter);
     activity_ui.build_user_sidebar();
 }

web/src/narrow_history.ts

@@ -34,7 +34,7 @@ function _save_narrow_state(): void {
         narrow_pointer,
         narrow_offset,
     };
-    history.replaceState(narrow_data, "", window.location.href);
+    browser_history.update_current_history_state_data(narrow_data);
 }
 
 // Safari limits you to 100 replaceState calls in 30 seconds.

web/src/stream_list.ts

@@ -9,6 +9,7 @@ import render_stream_subheader from "../templates/streams_subheader.hbs";
 import render_subscribe_to_more_streams from "../templates/subscribe_to_more_streams.hbs";
 
 import * as blueslip from "./blueslip";
+import * as browser_history from "./browser_history";
 import type {Filter} from "./filter";
 import * as hash_util from "./hash_util";
 import {$t} from "./i18n";
@@ -746,10 +747,21 @@ export function update_stream_sidebar_for_narrow(filter: Filter): JQuery | undef
     return $stream_li;
 }
 
-export function handle_narrow_activated(filter: Filter): void {
+export function handle_narrow_activated(
+    filter: Filter,
+    change_hash: boolean,
+    show_more_topics: boolean,
+): void {
     const $stream_li = update_stream_sidebar_for_narrow(filter);
     if ($stream_li) {
         scroll_stream_into_view($stream_li);
+        if (!change_hash) {
+            if (!is_zoomed_in() && show_more_topics) {
+                zoom_in();
+            } else if (is_zoomed_in() && !show_more_topics) {
+                zoom_out();
+            }
+        }
     }
 }
 
@@ -805,6 +817,7 @@ export function initialize({
 
     $("#stream_filters").on("click", ".show-more-topics", (e) => {
         zoom_in();
+        browser_history.update_current_history_state_data({show_more_topics: true});
 
         e.preventDefault();
         e.stopPropagation();
@@ -812,6 +825,7 @@ export function initialize({
 
     $(".show-all-streams").on("click", (e) => {
         zoom_out();
+        browser_history.update_current_history_state_data({show_more_topics: false});
 
         e.preventDefault();
         e.stopPropagation();

web/tests/narrow_activate.test.js

@@ -6,6 +6,7 @@ const {mock_esm, set_global, zrequire} = require("./lib/namespace");
 const {run_test, noop} = require("./lib/test");
 const $ = require("./lib/zjquery");
 
+set_global("history", {});
 mock_esm("../src/resize", {
     resize_stream_filters_container() {},
 });
@@ -46,7 +47,7 @@ const message_view_header = mock_esm("../src/message_view_header");
 const message_viewport = mock_esm("../src/message_viewport");
 const narrow_history = mock_esm("../src/narrow_history");
 const narrow_title = mock_esm("../src/narrow_title");
-const stream_list = mock_esm("../src/stream_list");
+const stream_list = mock_esm("../src/stream_list", {is_zoomed_in: () => false});
 const left_sidebar_navigation_area = mock_esm("../src/left_sidebar_navigation_area");
 const typing_events = mock_esm("../src/typing_events");
 const unread_ops = mock_esm("../src/unread_ops");