message_list_view: Move "is_search_view" to narrow_state.

This helper function is only ever used to describe the current view,
so it might as well be in the module for such views.

Also added the test coverage for "is_search_view".

web/src/message_list_view.ts

@@ -428,14 +428,6 @@ function maybe_restore_focus_to_message_edit_form(): void {
     }, 0);
 }
 
-function is_search_view(): boolean {
-    const current_filter = narrow_state.filter();
-    if (current_filter && !current_filter.supports_collapsing_recipients()) {
-        return true;
-    }
-    return false;
-}
-
 type SubscriptionMarkers = {
     bookend_top: boolean;
     stream_name: string;
@@ -456,7 +448,7 @@ function populate_group_from_message(
 
     // Each searched message is a self-contained result,
     // so we always display date in the recipient bar for those messages.
-    const always_display_date = is_search_view();
+    const always_display_date = narrow_state.is_search_view();
     if (is_stream) {
         assert(message.type === "stream");
         // stream messages have string display_recipient

web/src/narrow_state.ts

@@ -25,6 +25,13 @@ export function search_terms(current_filter: Filter | undefined = filter()): Nar
     return current_filter.terms();
 }
 
+export function is_search_view(current_filter: Filter | undefined = filter()): boolean {
+    if (current_filter && !current_filter.supports_collapsing_recipients()) {
+        return true;
+    }
+    return false;
+}
+
 export function is_message_feed_visible(): boolean {
     // It's important that `message_lists.current` is the
     // source of truth for this since during the initial app load,

web/tests/narrow_state.test.cjs

@@ -87,6 +87,7 @@ test("narrowed", () => {
     assert.ok(!narrow_state.narrowed_by_pm_reply());
     assert.ok(!narrow_state.narrowed_by_topic_reply());
     assert.ok(narrow_state.narrowed_by_stream_reply());
+    assert.ok(!narrow_state.is_search_view());
 
     set_filter([["dm", "steve@zulip.com"]]);
     assert.ok(narrow_state.narrowed_to_pms());
@@ -94,6 +95,7 @@ test("narrowed", () => {
     assert.ok(narrow_state.narrowed_by_pm_reply());
     assert.ok(!narrow_state.narrowed_by_topic_reply());
     assert.ok(!narrow_state.narrowed_by_stream_reply());
+    assert.ok(!narrow_state.is_search_view());
 
     set_filter([
         ["stream", foo_stream_id.toString()],
@@ -104,6 +106,7 @@ test("narrowed", () => {
     assert.ok(!narrow_state.narrowed_by_pm_reply());
     assert.ok(narrow_state.narrowed_by_topic_reply());
     assert.ok(!narrow_state.narrowed_by_stream_reply());
+    assert.ok(!narrow_state.is_search_view());
 
     set_filter([["search", "grail"]]);
     assert.ok(!narrow_state.narrowed_to_pms());
@@ -111,6 +114,7 @@ test("narrowed", () => {
     assert.ok(!narrow_state.narrowed_by_pm_reply());
     assert.ok(!narrow_state.narrowed_by_topic_reply());
     assert.ok(!narrow_state.narrowed_by_stream_reply());
+    assert.ok(narrow_state.is_search_view());
 
     set_filter([["is", "starred"]]);
     assert.ok(!narrow_state.narrowed_to_pms());
@@ -118,6 +122,7 @@ test("narrowed", () => {
     assert.ok(!narrow_state.narrowed_by_pm_reply());
     assert.ok(!narrow_state.narrowed_by_topic_reply());
     assert.ok(!narrow_state.narrowed_by_stream_reply());
+    assert.ok(narrow_state.is_search_view());
 });
 
 test("terms", () => {