resolved_topic: Add and use predicate is_resolved.

We leave in place a couple of sites where the `startsWith` is
entangled with other string manipulation.  We'll handle those next.

frontend_tests/node_tests/compose_validate.js

@@ -770,7 +770,7 @@ test_ui("test warn_if_topic_resolved", ({override, mock_template}) => {
 
     mock_template("compose_resolved_topic.hbs", false, (context) => {
         assert.ok(context.can_move_topic);
-        assert.ok(context.topic_name.startsWith(resolved_topic.RESOLVED_TOPIC_PREFIX));
+        assert.ok(resolved_topic.is_resolved(context.topic_name));
         return "fake-compose_resolved_topic";
     });
 

frontend_tests/node_tests/resolved_topic.js

@@ -0,0 +1,20 @@
+"use strict";
+
+const {strict: assert} = require("assert");
+
+const {zrequire} = require("../zjsunit/namespace");
+const {run_test} = require("../zjsunit/test");
+
+const resolved_topic = zrequire("../shared/js/resolved_topic");
+
+const topic_name = "asdf";
+const resolved_name = "✔ " + topic_name;
+const overresolved_name = "✔ ✔✔ " + topic_name;
+const pseudoresolved_name = "✔" + topic_name; // check mark, but no space
+
+run_test("is_resolved", () => {
+    assert.ok(!resolved_topic.is_resolved(topic_name));
+    assert.ok(resolved_topic.is_resolved(resolved_name));
+    assert.ok(resolved_topic.is_resolved(overresolved_name));
+    assert.ok(!resolved_topic.is_resolved(pseudoresolved_name));
+});

static/js/compose_validate.js

@@ -178,7 +178,7 @@ export function warn_if_topic_resolved() {
 
     const sub = stream_data.get_sub(stream_name);
 
-    if (sub && topic_name.startsWith(resolved_topic.RESOLVED_TOPIC_PREFIX)) {
+    if (sub && resolved_topic.is_resolved(topic_name)) {
         const error_area = $("#compose_resolved_topic");
 
         if (error_area.html()) {

static/js/filter.js

@@ -96,10 +96,7 @@ function message_matches_search_term(message, operator, operand) {
                 case "unread":
                     return unread.message_unread(message);
                 case "resolved":
-                    return (
-                        message.type === "stream" &&
-                        message.topic.startsWith(resolved_topic.RESOLVED_TOPIC_PREFIX)
-                    );
+                    return message.type === "stream" && resolved_topic.is_resolved(message.topic);
                 default:
                     return false; // is:whatever returns false
             }

static/js/message_list_view.js

@@ -182,7 +182,7 @@ function populate_group_from_message_container(group, message_container) {
         } else {
             group.stream_id = sub.stream_id;
         }
-        group.topic_is_resolved = group.topic.startsWith(resolved_topic.RESOLVED_TOPIC_PREFIX);
+        group.topic_is_resolved = resolved_topic.is_resolved(group.topic);
         group.topic_muted = muted_topics.is_topic_muted(group.stream_id, group.topic);
     } else if (group.is_private) {
         group.pm_with_url = message_container.pm_with_url;

static/js/stream_popover.js

@@ -291,7 +291,7 @@ function build_topic_popover(opts) {
         topic_muted,
         can_move_topic,
         is_realm_admin: page_params.is_admin,
-        topic_is_resolved: topic_name.startsWith(resolved_topic.RESOLVED_TOPIC_PREFIX),
+        topic_is_resolved: resolved_topic.is_resolved(topic_name),
         color: sub.color,
         has_starred_messages,
     });

static/shared/js/resolved_topic.js

@@ -1,2 +1,6 @@
 /** The canonical form of the resolved-topic prefix. */
 export const RESOLVED_TOPIC_PREFIX = "✔ ";
+
+export function is_resolved(topic_name) {
+    return topic_name.startsWith(RESOLVED_TOPIC_PREFIX);
+}

static/shared/js/resolved_topic.js.flow

@@ -1,3 +1,5 @@
 // @flow strict
 
 declare export var RESOLVED_TOPIC_PREFIX: string;
+
+declare export function is_resolved(topic_name: string): boolean;