From 5e668118751b50aaf7f6ab675dd5dc628ced30bc Mon Sep 17 00:00:00 2001
From: John MacFarlane <jgm@berkeley.edu>
Date: Fri, 20 Oct 2023 10:27:49 -0700
Subject: [PATCH] Markdown reader: fix blindspot with superscript in links.

Previously `[^super^](#ref)` wasn't parsed as a link, due to
code that was meant to prevent footnote markers from being
recognized as reference links.  This commit tightens up that
code to avoid this bad effect.

We have also added a new restriction on footnote labels: they
cannot contain the characters `^`, `[`, or `]`. Though this is
technically a breaking change, we suspect that the impact will
be minimal, as it's very unlikely people would be using these
characters in their note labels.

Closes #8981.
---
 MANUAL.txt                          |  6 +++---
 src/Text/Pandoc/Readers/Markdown.hs | 12 ++++--------
 test/command/8981.md                |  6 ++++++
 3 files changed, 13 insertions(+), 11 deletions(-)
 create mode 100644 test/command/8981.md

diff --git a/MANUAL.txt b/MANUAL.txt
index d3be3b69cc85..b56121d95e15 100644
--- a/MANUAL.txt
+++ b/MANUAL.txt
@@ -5509,9 +5509,9 @@ Pandoc's Markdown allows footnotes, using the following syntax:
     isn't indented.
 
 The identifiers in footnote references may not contain spaces, tabs,
-or newlines.  These identifiers are used only to correlate the
-footnote reference with the note itself; in the output, footnotes
-will be numbered sequentially.
+newlines, or the characters `^`, `[`, or `]`. These identifiers
+are used only to correlate the footnote reference with the note
+itself; in the output, footnotes will be numbered sequentially.
 
 The footnotes themselves need not be placed at the end of the
 document.  They may appear anywhere except inside other block elements
diff --git a/src/Text/Pandoc/Readers/Markdown.hs b/src/Text/Pandoc/Readers/Markdown.hs
index 731ca07a665d..402893897da5 100644
--- a/src/Text/Pandoc/Readers/Markdown.hs
+++ b/src/Text/Pandoc/Readers/Markdown.hs
@@ -142,12 +142,6 @@ isHruleChar _   = False
 setextHChars :: [Char]
 setextHChars = "=-"
 
-isBlank :: Char -> Bool
-isBlank ' '  = True
-isBlank '\t' = True
-isBlank '\n' = True
-isBlank _    = False
-
 --
 -- auxiliary functions
 --
@@ -416,7 +410,9 @@ abbrevKey = do
     return $ return mempty
 
 noteMarker :: PandocMonad m => MarkdownParser m Text
-noteMarker = string "[^" >> many1TillChar (satisfy $ not . isBlank) (char ']')
+noteMarker = string "[^" >>
+  many1TillChar (satisfy (`notElem` ['\r','\n','\t',' ','^','[',']']))
+                (char ']')
 
 rawLine :: PandocMonad m => MarkdownParser m Text
 rawLine = try $ do
@@ -1815,7 +1811,7 @@ endline = try $ do
 -- a reference label for a link
 reference :: PandocMonad m => MarkdownParser m (F Inlines, Text)
 reference = do
-  guardDisabled Ext_footnotes <|> notFollowedBy' (string "[^")
+  guardDisabled Ext_footnotes <|> notFollowedBy' noteMarker
   withRaw $ trimInlinesF <$> inlinesInBalancedBrackets
 
 parenthesizedChars :: PandocMonad m => MarkdownParser m Text
diff --git a/test/command/8981.md b/test/command/8981.md
new file mode 100644
index 000000000000..00ba6d23176c
--- /dev/null
+++ b/test/command/8981.md
@@ -0,0 +1,6 @@
+```
+% pandoc --wrap=none
+consectetur [^\[link\]^](#ref "Title")
+^D
+<p>consectetur <a href="#ref" title="Title"><sup>[link]</sup></a></p>
+```