From 327647f4f8e7449f00ffbebb4102b31b7b660919 Mon Sep 17 00:00:00 2001
From: Kislay Udbhav Verma <kislayuv27@gmail.com>
Date: Wed, 9 Oct 2024 00:47:19 +0530
Subject: [PATCH] copy_and_paste: Paste fallback md link if syntax link will be
 broken.

If we paste a stream-topic URL that can be formatted as per #29302,
we now generate a normal markdown link if the stream topic syntax
could result in a broken link.

Fixes #31904
---
 web/src/copy_and_paste.ts        |  7 +++++--
 web/tests/copy_and_paste.test.js | 31 ++++++++++++++++++++++++++-----
 2 files changed, 31 insertions(+), 7 deletions(-)

diff --git a/web/src/copy_and_paste.ts b/web/src/copy_and_paste.ts
index 051403bd5a..892444a053 100644
--- a/web/src/copy_and_paste.ts
+++ b/web/src/copy_and_paste.ts
@@ -666,18 +666,21 @@ export function try_stream_topic_syntax_text(text: string): string | null {
         return null;
     }
 
+    // Now we're sure that the URL is a valid stream topic URL.
+    // But the produced #**stream>topic** syntax could be broken.
+
     const stream = stream_data.get_sub_by_id(stream_topic.stream_id);
     assert(stream !== undefined);
     const stream_name = stream.name;
     if (topic_link_util.will_produce_broken_stream_topic_link(stream_name)) {
-        return null;
+        return topic_link_util.get_fallback_markdown_link(stream_name, stream_topic.topic_name);
     }
 
     if (
         stream_topic.topic_name !== undefined &&
         topic_link_util.will_produce_broken_stream_topic_link(stream_topic.topic_name)
     ) {
-        return null;
+        return topic_link_util.get_fallback_markdown_link(stream_name, stream_topic.topic_name);
     }
 
     let syntax_text = "#**" + stream_name;
diff --git a/web/tests/copy_and_paste.test.js b/web/tests/copy_and_paste.test.js
index 449151bec7..98674b0aaf 100644
--- a/web/tests/copy_and_paste.test.js
+++ b/web/tests/copy_and_paste.test.js
@@ -12,6 +12,10 @@ stream_data.add_sub({
     stream_id: 4,
     name: "Rome",
 });
+stream_data.add_sub({
+    stream_id: 5,
+    name: "Romeo`s lair",
+});
 
 run_test("try_stream_topic_syntax_text", () => {
     const test_cases = [
@@ -41,11 +45,28 @@ run_test("try_stream_topic_syntax_text", () => {
         ["http://zulip.zulipdev.com/#narrow/topic/cheese"],
         ["http://zulip.zulipdev.com/#narrow/topic/pizza/stream/Rome"],
 
-        // characters which are known to produce broken #**stream>topic** urls.
-        ["http://zulip.zulipdev.com/#narrow/channel/4-Rome/topic/100.25.20profits.60"],
-        ["http://zulip.zulipdev.com/#narrow/channel/4-Rome/topic/100.25.20*profits"],
-        ["http://zulip.zulipdev.com/#narrow/channel/4-Rome/topic/.24.24 100.25.20profits"],
-        ["http://zulip.zulipdev.com/#narrow/channel/4-Rome/topic/>100.25.20profits"],
+        // When a url containing characters which are known to produce broken
+        // #**stream>topic** urls is pasted, a normal markdown link syntax is produced.
+        [
+            "http://zulip.zulipdev.com/#narrow/stream/4-Rome/topic/100.25.20profits.60",
+            "[#Rome>100% profits&#96;](#narrow/channel/4-Rome/topic/100.25.20profits.60)",
+        ],
+        [
+            "http://zulip.zulipdev.com/#narrow/stream/4-Rome/topic/100.25.20*profits",
+            "[#Rome>100% &#42;profits](#narrow/channel/4-Rome/topic/100.25.20*profits)",
+        ],
+        [
+            "http://zulip.zulipdev.com/#narrow/stream/4-Rome/topic/.24.24 100.25.20profits",
+            "[#Rome>&#36;&#36; 100% profits](#narrow/channel/4-Rome/topic/.24.24.20100.25.20profits)",
+        ],
+        [
+            "http://zulip.zulipdev.com/#narrow/stream/4-Rome/topic/>100.25.20profits",
+            "[#Rome>&gt;100% profits](#narrow/channel/4-Rome/topic/.3E100.25.20profits)",
+        ],
+        [
+            "http://zulip.zulipdev.com/#narrow/stream/5-Romeo.60s-lair/topic/normal",
+            "[#Romeo&#96;s lair>normal](#narrow/channel/5-Romeo.60s-lair/topic/normal)",
+        ],
     ];
 
     for (const test_case of test_cases) {