recent_topics: Fix searching for special characters.

Escape all the possible special characters.
We replaced \b with (?:^|\s) since it matches word boundries including
special characters.

Pasted relevant stackoverflow links which expain them properly.

frontend_tests/node_tests/recent_topics.js

@@ -708,3 +708,34 @@ run_test('test_topic_edit', () => {
     assert.equal(all_topics.get(get_topic_key(stream2, topic1)), undefined);
     verify_topic_data(all_topics, stream3, topic9, messages[0].id, true);
 });
+
+run_test('test_search', () => {
+    const rt = zrequire('recent_topics');
+    assert.equal(rt.topic_in_search_results('t', 'Recent Topic'), true);
+    assert.equal(rt.topic_in_search_results('T', 'Recent Topic'), true);
+    assert.equal(rt.topic_in_search_results('to', 'Recent Topic'), true);
+    assert.equal(rt.topic_in_search_results('top', 'Recent Topic'), true);
+    assert.equal(rt.topic_in_search_results('ToP', 'Recent Topic'), true);
+    assert.equal(rt.topic_in_search_results('Topi', 'Recent Topic'), true);
+    assert.equal(rt.topic_in_search_results('tOpi', 'Recent Topic'), true);
+    assert.equal(rt.topic_in_search_results('toPic', 'Recent Topic'), true);
+    assert.equal(rt.topic_in_search_results('Topic', 'Recent Topic'), true);
+    assert.equal(rt.topic_in_search_results('topic', 'Recent Topic'), true);
+    assert.equal(rt.topic_in_search_results('recent', 'Recent Topic'), true);
+    assert.equal(rt.topic_in_search_results('RECENT', 'Recent Topic'), true);
+
+    // Matches only comple words or from the start of words.
+    assert.equal(rt.topic_in_search_results('o', 'Recent Topic'), false);
+
+    assert.equal(rt.topic_in_search_results('?', 'Recent Topic'), false);
+
+    // Test special character match
+    assert.equal(rt.topic_in_search_results('.*+?^${}()[]\\', 'Recent Topic'), false);
+    assert.equal(rt.topic_in_search_results('?', 'not-at-start?'), false);
+
+    assert.equal(rt.topic_in_search_results('?', '?'), true);
+    assert.equal(rt.topic_in_search_results('?', '\\?'), false);
+
+    assert.equal(rt.topic_in_search_results('\\', '\\'), true);
+    assert.equal(rt.topic_in_search_results('\\', '\\\\'), true);
+});

static/js/recent_topics.js

@@ -215,20 +215,24 @@ exports.process_topic_edit = function (old_stream_id, old_topic, new_topic, new_
     exports.process_messages(new_topic_msgs);
 };
 
-function topic_in_search_results(keyword, stream, topic) {
+exports.topic_in_search_results = function (keyword, stream, topic) {
     if (keyword === "") {
         return true;
     }
+    // Escape speacial characters from input.
+    // https://stackoverflow.com/questions/3446170/escape-string-for-use-in-javascript-regex
+    keyword = keyword.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
     // split the search text around whitespace(s).
     // eg: "Denamark recent" -> ["Denamrk", "recent"]
     const search_keywords = $.trim(keyword).split(/\s+/);
     // turn the search keywords into word boundary groups
-    // eg: ["Denamrk", "recent"] -> "^(?=.*\bDenmark\b)(?=.*\brecent\b).*$"
-    const val = '^(?=.*\\b' + search_keywords.join('\\b)(?=.*\\b') + ').*$';
+    // eg: ["Denamrk", "recent"] -> "^(?=.*(?:^|\s)Denmark(?:^|\s))(?=.*(?:^|\s)Recent).*$"
+    // https://stackoverflow.com/questions/10590098/javascript-regexp-word-boundaries-unicode-characters
+    const val = '^(?=.*(?:^|\\s)' + search_keywords.join('(?:^|\\s))(?=.*(?:^|\\s)') + ').*$';
     const reg = RegExp(val, 'i'); // i for ignorecase
     const text = (stream + " " + topic).replace(/\s+/g, ' ');
     return reg.test(text);
-}
+};
 
 function filters_should_hide_topic(topic_data) {
     const msg = message_store.get(topic_data.last_msg_id);
@@ -253,7 +257,7 @@ function filters_should_hide_topic(topic_data) {
     }
 
     const search_keyword = $("#recent_topics_search").val();
-    if (!topic_in_search_results(search_keyword, msg.stream, msg.topic)) {
+    if (!recent_topics.topic_in_search_results(search_keyword, msg.stream, msg.topic)) {
         return true;
     }