narrow_state: Remove narrowed_to_topic function.

This was only being used in one place in compose_closed_ui
to create the label for the closed composebox. But it
only checked if the `channel` and `topic` filters existed,
while `stream_sub` can return `undefined` for a few other
reasons. To ensure that we're catching the undefined sub
while also avoiding duplicate work, it makes sense to just
call `stream_sub()` directly.

Fixes this bug:
https://zulip.sentry.io/issues/5367251929/events/40073ecf007a4a9798e728061a576377/?project=450455688282112

web/src/compose_closed_ui.ts

@@ -1,5 +1,4 @@
 import $ from "jquery";
-import assert from "minimalistic-assert";
 
 import * as compose_actions from "./compose_actions";
 import {$t} from "./i18n";
@@ -28,7 +27,6 @@ export function get_recipient_label(message?: ComposeClosedMessage): string {
     // actual message objects with fake objects containing just a
     // couple fields, both those constructed here and potentially
     // passed in.
-
     if (message_lists.current === undefined) {
         return "";
     }
@@ -38,12 +36,9 @@ export function get_recipient_label(message?: ComposeClosedMessage): string {
             // For empty narrows where there's a clear reply target,
             // i.e. stream+topic or a single direct message conversation,
             // we label the button as replying to the thread.
-            if (narrow_state.narrowed_to_topic()) {
-                const stream = narrow_state.stream_sub();
-                assert(stream !== undefined);
-                const stream_id = stream.stream_id;
-                const topic = narrow_state.topic();
-                assert(topic !== undefined);
+            const stream_id = narrow_state.stream_sub()?.stream_id;
+            const topic = narrow_state.topic();
+            if (stream_id !== undefined && topic !== undefined) {
                 return format_stream_recipient_label(stream_id, topic);
             } else if (narrow_state.pm_ids_string()) {
                 const user_ids = people.user_ids_string_to_ids_array(narrow_state.pm_ids_string()!);

web/src/narrow_state.ts

@@ -138,6 +138,7 @@ export function stream_sub(
         return undefined;
     }
     const stream_operands = current_filter.operands("channel");
+
     if (stream_operands.length !== 1) {
         return undefined;
     }
@@ -357,13 +358,6 @@ export function narrowed_by_stream_reply(current_filter: Filter | undefined = fi
     return terms.length === 1 && current_filter.operands("channel").length === 1;
 }
 
-export function narrowed_to_topic(current_filter: Filter | undefined = filter()): boolean {
-    if (current_filter === undefined) {
-        return false;
-    }
-    return current_filter.has_operator("channel") && current_filter.has_operator("topic");
-}
-
 export function is_for_stream_id(stream_id: number, filter?: Filter): boolean {
     // This is not perfect, since we still track narrows by
     // name, not id, but at least the interface is good going

web/tests/narrow_state.test.js

@@ -74,7 +74,6 @@ test("narrowed", () => {
     assert.ok(!narrow_state.narrowed_by_reply());
     assert.ok(!narrow_state.narrowed_by_pm_reply());
     assert.ok(!narrow_state.narrowed_by_topic_reply());
-    assert.ok(!narrow_state.narrowed_to_topic());
     assert.ok(!narrow_state.narrowed_by_stream_reply());
     assert.equal(narrow_state.stream_sub(), undefined);
 
@@ -83,15 +82,13 @@ test("narrowed", () => {
     assert.ok(!narrow_state.narrowed_by_reply());
     assert.ok(!narrow_state.narrowed_by_pm_reply());
     assert.ok(!narrow_state.narrowed_by_topic_reply());
-    assert.ok(!narrow_state.narrowed_to_topic());
     assert.ok(narrow_state.narrowed_by_stream_reply());
 
     set_filter([["dm", "steve@zulip.com"]]);
     assert.ok(narrow_state.narrowed_to_pms());
     assert.ok(narrow_state.narrowed_by_reply());
     assert.ok(narrow_state.narrowed_by_pm_reply());
     assert.ok(!narrow_state.narrowed_by_topic_reply());
-    assert.ok(!narrow_state.narrowed_to_topic());
     assert.ok(!narrow_state.narrowed_by_stream_reply());
 
     set_filter([
@@ -110,15 +107,13 @@ test("narrowed", () => {
     assert.ok(!narrow_state.narrowed_by_reply());
     assert.ok(!narrow_state.narrowed_by_pm_reply());
     assert.ok(!narrow_state.narrowed_by_topic_reply());
-    assert.ok(!narrow_state.narrowed_to_topic());
     assert.ok(!narrow_state.narrowed_by_stream_reply());
 
     set_filter([["is", "starred"]]);
     assert.ok(!narrow_state.narrowed_to_pms());
     assert.ok(!narrow_state.narrowed_by_reply());
     assert.ok(!narrow_state.narrowed_by_pm_reply());
     assert.ok(!narrow_state.narrowed_by_topic_reply());
-    assert.ok(!narrow_state.narrowed_to_topic());
     assert.ok(!narrow_state.narrowed_by_stream_reply());
 });