Markdown writer: avoid unnecessary escapes before intraword _

when `intraword_underscores` extension is enabled.
Closes #6296.

src/Text/Pandoc/Writers/Markdown.hs

@@ -313,7 +313,12 @@ escapeText opts =
               case cs of
                    '.':'.':rest -> '\\':'.':'.':'.':go rest
                    _            -> '.':go cs
-       _   -> c : go cs
+       _   -> case cs of
+                '_':x:xs
+                  | isEnabled Ext_intraword_underscores opts
+                  , isAlphaNum c
+                  , isAlphaNum x -> c : '_' : x : go xs
+                _                -> c : go cs
 
 attrsToMarkdown :: Attr -> Doc Text
 attrsToMarkdown attribs = braces $ hsep [attribId, attribClasses, attribKeys]

test/command/6296.md

@@ -0,0 +1,14 @@
+```
+% pandoc -f native -t markdown
+[Str "_hi_there"]
+^D
+\_hi_there
+```
+
+```
+% pandoc -f native -t markdown-intraword_underscores
+[Str "_hi_there"]
+^D
+\_hi\_there
+```
+

test/writer.markdown

@@ -683,7 +683,7 @@ Just a [URL](/url/).
 
 [URL and title](/url/ "title with single quotes")
 
-[with\_underscore](/url/with_underscore)
+[with_underscore](/url/with_underscore)
 
 [Email link](mailto:nobody@nowhere.net)