From 2c0e989f9df788b7f168159fd99d5c3e1a78aa85 Mon Sep 17 00:00:00 2001
From: John MacFarlane <jgm@berkeley.edu>
Date: Mon, 7 Aug 2017 21:00:57 -0700
Subject: [PATCH] Markdown reader:  fixed spurious parsing as citation as
 reference def.

We now disallow reference keys starting with `@` if the
`citations` extension is enabled.  Closes #3840.
---
 src/Text/Pandoc/Readers/Markdown.hs |  6 ++++--
 test/command/3840.md                | 15 +++++++++++++++
 2 files changed, 19 insertions(+), 2 deletions(-)
 create mode 100644 test/command/3840.md

diff --git a/src/Text/Pandoc/Readers/Markdown.hs b/src/Text/Pandoc/Readers/Markdown.hs
index d7e59c7fd..1bcf1cfae 100644
--- a/src/Text/Pandoc/Readers/Markdown.hs
+++ b/src/Text/Pandoc/Readers/Markdown.hs
@@ -1695,8 +1695,10 @@ endline = try $ do
 
 -- a reference label for a link
 reference :: PandocMonad m => MarkdownParser m (F Inlines, String)
-reference = do notFollowedBy' (string "[^")   -- footnote reference
-               withRaw $ trimInlinesF <$> inlinesInBalancedBrackets
+reference = do
+  guardDisabled Ext_footnotes <|> notFollowedBy' (string "[^")
+  guardDisabled Ext_citations <|> notFollowedBy' (string "[@")
+  withRaw $ trimInlinesF <$> inlinesInBalancedBrackets
 
 parenthesizedChars :: PandocMonad m => MarkdownParser m [Char]
 parenthesizedChars = do
diff --git a/test/command/3840.md b/test/command/3840.md
new file mode 100644
index 000000000..ceb1d1e51
--- /dev/null
+++ b/test/command/3840.md
@@ -0,0 +1,15 @@
+```
+% pandoc
+[@Alhazen1572-qk, V.9]: "competentius est"
+^D
+<p><span class="citation" data-cites="Alhazen1572-qk">[@Alhazen1572-qk, V.9]</span>: “competentius est”</p>
+```
+
+```
+% pandoc -f markdown-citations
+[@Alhazen1572-qk, V.9]: "competentius est"
+
+[@Alhazen1572-qk, V.9]
+^D
+<p><a href="" title="competentius est">@Alhazen1572-qk, V.9</a></p>
+```