Markdown reader: fix small super/subscript issue.

Superscripts and subscripts cannot contain spaces,
but newlines were previously allowed (unintentionally).
This led to bad interactions in some cases with footnotes.
E.g.

```
foo^[note]
bar^[note]
```

With this change newlines are also not allowed inside
super/subscripts.

Closes #5878.

1 files changed, 6 insertions, 2 deletions

diff --git a/src/Text/Pandoc/Readers/Markdown.hs b/src/Text/Pandoc/Readers/Markdown.hs
index 46220acc8..4807baada 100644
--- a/src/Text/Pandoc/Readers/Markdown.hs
+++ b/src/Text/Pandoc/Readers/Markdown.hs
@@ -1700,13 +1700,17 @@ superscript :: PandocMonad m => MarkdownParser m (F Inlines)
 superscript = fmap B.superscript <$> try (do
   guardEnabled Ext_superscript
   char '^'
-  mconcat <$> many1Till (notFollowedBy spaceChar >> inline) (char '^'))
+  mconcat <$> many1Till (do notFollowedBy spaceChar
+                            notFollowedBy newline
+                            inline) (char '^'))
 
 subscript :: PandocMonad m => MarkdownParser m (F Inlines)
 subscript = fmap B.subscript <$> try (do
   guardEnabled Ext_subscript
   char '~'
-  mconcat <$> many1Till (notFollowedBy spaceChar >> inline) (char '~'))
+  mconcat <$> many1Till (do notFollowedBy spaceChar
+                            notFollowedBy newline
+                            inline) (char '~'))
 
 whitespace :: PandocMonad m => MarkdownParser m (F Inlines)
 whitespace = spaceChar >> return <$> (lb <|> regsp) <?> "whitespace"