From 2c58fbaa29671ec33a879f2bb3724068529c47ff Mon Sep 17 00:00:00 2001
From: "Thiemo Kreuz (WMDE)" <thiemo.kreuz@wikimedia.de>
Date: Tue, 26 Jun 2018 09:55:21 +0000
Subject: [PATCH] Linker: more consistent whitespace parsing in
 formatLinksInComment

Try to paste and preview this in the wikitext as well as the summary
line: [[:a]] [[ :a]]

The wikitext will show "a a", but the summary line will show "a :a".
This is only a display issue, all 4 links correctly link to the
article [[A]].

Change-Id: I08253a6d0b55b9aa3eace519bbdc1a456400bf84
---
 includes/Linker.php                   | 1 +
 tests/phpunit/includes/LinkerTest.php | 5 +++++
 2 files changed, 6 insertions(+)

diff --git a/includes/Linker.php b/includes/Linker.php
index 0ee6c92f77..c0959bf634 100644
--- a/includes/Linker.php
+++ b/includes/Linker.php
@@ -1221,6 +1221,7 @@ class Linker {
 		return preg_replace_callback(
 			'/
 				\[\[
+				\s*+ # ignore leading whitespace, the *+ quantifier disallows backtracking
 				:? # ignore optional leading colon
 				([^\]|]+) # 1. link target; page names cannot include ] or |
 				(?:\|
diff --git a/tests/phpunit/includes/LinkerTest.php b/tests/phpunit/includes/LinkerTest.php
index 4c508e3851..b8aecc05a5 100644
--- a/tests/phpunit/includes/LinkerTest.php
+++ b/tests/phpunit/includes/LinkerTest.php
@@ -294,6 +294,11 @@ class LinkerTest extends MediaWikiLangTestCase {
 				'foo bar [[Special:BlankPage]]',
 				null,
 			],
+			[
+				'<a href="/wiki/Special:BlankPage" title="Special:BlankPage">Special:BlankPage</a>',
+				'[[ :Special:BlankPage]]',
+				null,
+			],
 			[
 				'<a class="external" rel="nofollow" href="//en.example.org/w/Foo%27bar">Foo\'bar</a>',
 				"[[Foo'bar]]",
-- 
2.20.1