MediaWiki writer: prevent triple [[[.

This confuses mediawiki's parser.  So we insert a `<nowiki/>`
no-op between a literal `[` and a link.  Closes #6119.

src/Text/Pandoc/Writers/MediaWiki.hs

@@ -347,7 +347,17 @@ blockListToMediaWiki blocks =
 -- | Convert list of Pandoc inline elements to MediaWiki.
 inlineListToMediaWiki :: PandocMonad m => [Inline] -> MediaWikiWriter m Text
 inlineListToMediaWiki lst =
-  fmap T.concat $ mapM inlineToMediaWiki lst
+  fmap T.concat $ mapM inlineToMediaWiki $ fixup lst
+    where
+     fixup [] = []
+     fixup (Str t : x : xs)
+       | not (T.null t) && T.last t == '['
+       , isLinkOrImage x =
+          Str t : RawInline (Format "mediawiki") "<nowiki/>" : x : fixup xs
+     fixup (x:xs) = x : fixup xs
+     isLinkOrImage (Link{})  = True
+     isLinkOrImage (Image{}) = True
+     isLinkOrImage _         = False
 
 -- | Convert Pandoc inline element to MediaWiki.
 inlineToMediaWiki :: PandocMonad m => Inline -> MediaWikiWriter m Text

test/command/6119.md

@@ -0,0 +1,10 @@
+```
+% pandoc -t mediawiki
+[[link](url)]
+
+[![image](url)]
+^D
+[<nowiki/>[[url|link]]]
+
+[<nowiki/>[[File:url|image]]]
+```