From 32f9ee7a62cdeb9cca5b694dc0fdb805dbcbff87 Mon Sep 17 00:00:00 2001
From: Kislay Verma <kislayuv27@gmail.com>
Date: Sat, 25 Jan 2025 17:21:02 +0530
Subject: [PATCH] topic_link_util: Add `[` and `]` as characters to escape.

These characters cause the fallback markdown
links produced (#30071) to be broken.

Broken links are not produced when these are present
in `#**channel>topic**` syntax. It is only a problem
with the fallback markdown links.
---
 web/src/topic_link_util.ts         |  6 +++++-
 web/tests/topic_link_util.test.cjs | 22 ++++++++++++++++++++++
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/web/src/topic_link_util.ts b/web/src/topic_link_util.ts
index 0fb484a33f..06b7778a7e 100644
--- a/web/src/topic_link_util.ts
+++ b/web/src/topic_link_util.ts
@@ -4,7 +4,7 @@ import * as internal_url from "../shared/src/internal_url.ts";
 
 import * as stream_data from "./stream_data.ts";
 
-const invalid_stream_topic_regex = /[`>*&]|(\$\$)/g;
+const invalid_stream_topic_regex = /[`>*&[\]]|(\$\$)/g;
 
 export function will_produce_broken_stream_topic_link(word: string): boolean {
     return invalid_stream_topic_regex.test(word);
@@ -22,6 +22,10 @@ export function escape_invalid_stream_topic_characters(text: string): string {
             return "&amp;";
         case "$$":
             return "&#36;&#36;";
+        case "[":
+            return "&#91;";
+        case "]":
+            return "&#93;";
         default:
             return text;
     }
diff --git a/web/tests/topic_link_util.test.cjs b/web/tests/topic_link_util.test.cjs
index 6e2f46f7ba..60a823a930 100644
--- a/web/tests/topic_link_util.test.cjs
+++ b/web/tests/topic_link_util.test.cjs
@@ -32,9 +32,18 @@ const dollar_stream = {
     type: "stream",
 };
 
+const markdown_stream = {
+    name: "Markdown [md]",
+    description: "markdown",
+    stream_id: 7,
+    subscribed: true,
+    type: "stream",
+};
+
 stream_data.add_sub(sweden_stream);
 stream_data.add_sub(denmark_stream);
 stream_data.add_sub(dollar_stream);
+stream_data.add_sub(markdown_stream);
 
 run_test("stream_topic_link_syntax_test", () => {
     assert.equal(
@@ -78,11 +87,24 @@ run_test("stream_topic_link_syntax_test", () => {
         topic_link_util.get_fallback_markdown_link("$$MONEY$$"),
         "[#&#36;&#36;MONEY&#36;&#36;](#narrow/channel/6-.24.24MONEY.24.24)",
     );
+    assert.equal(
+        topic_link_util.get_fallback_markdown_link("Markdown [md]"),
+        "[#Markdown &#91;md&#93;](#narrow/channel/7-Markdown-.5Bmd.5D)",
+    );
 
     assert.equal(
         topic_link_util.get_stream_topic_link_syntax("Sweden", "&ab"),
         "[#Sweden > &amp;ab](#narrow/channel/1-Sweden/topic/.26ab)",
     );
+    assert.equal(
+        topic_link_util.get_stream_topic_link_syntax("Sweden", "&ab]"),
+        "[#Sweden > &amp;ab&#93;](#narrow/channel/1-Sweden/topic/.26ab.5D)",
+    );
+
+    assert.equal(
+        topic_link_util.get_stream_topic_link_syntax("Sweden", "&a[b"),
+        "[#Sweden > &amp;a&#91;b](#narrow/channel/1-Sweden/topic/.26a.5Bb)",
+    );
 
     // Only for full coverage of the module.
     assert.equal(topic_link_util.escape_invalid_stream_topic_characters("Sweden"), "Sweden");