CommonMark: add support for wiki links. [API change]

Adds commonmark extensions `wikilinks_title_after_pipe` and
`wikilinks_title_before_pipe`. The former enables links of style `[[Name
of page|Title]]` and the latter `[[Title|Name of page]]`. Titles are
optional in both variants, so this works for both:
`[[https://example.org]]`, `[[Name of page]]`.

The writer is modified to render links with title `wikilink` as a
wikilink if a respective extension is enabled.

Pandoc will use `wikilinks_title_after_pipe` if both extensions are
enabled.

Closes: #2923

src/Text/Pandoc/Extensions.hs

@@ -134,6 +134,10 @@ data Extension =
     | Ext_tex_math_dollars    -- ^ TeX math between $..$ or $$..$$
     | Ext_tex_math_double_backslash  -- ^ TeX math btw \\(..\\) \\[..\\]
     | Ext_tex_math_single_backslash  -- ^ TeX math btw \(..\) \[..\]
+    | Ext_wikilinks_title_after_pipe -- ^ Support wikilinks of style
+                                     -- [[target|title]]
+    | Ext_wikilinks_title_before_pipe  -- ^ Support wikilinks of style
+                                       -- [[title|target]]
     | Ext_xrefs_name          -- ^ Use xrefs with names
     | Ext_xrefs_number        -- ^ Use xrefs with numbers
     | Ext_yaml_metadata_block -- ^ YAML metadata block
@@ -526,6 +530,8 @@ getAllExtensions f = universalExtensions <> getAll f
     , Ext_implicit_header_references
     , Ext_attributes
     , Ext_sourcepos
+    , Ext_wikilinks_title_after_pipe
+    , Ext_wikilinks_title_before_pipe
     , Ext_yaml_metadata_block
     , Ext_rebase_relative_paths
     ]
@@ -628,4 +634,3 @@ parseFormatSpec = parse formatSpec ""
                     case polarity of
                         '+' -> (ext : extsToEnable, extsToDisable)
                         _   -> (extsToEnable, ext : extsToDisable)
-

src/Text/Pandoc/Readers/CommonMark.hs

@@ -113,6 +113,9 @@ specFor opts = foldr ($) defaultSyntaxSpec exts
          [ (footnoteSpec <>) | isEnabled Ext_footnotes opts ] ++
          [ (definitionListSpec <>) | isEnabled Ext_definition_lists opts ] ++
          [ (taskListSpec <>) | isEnabled Ext_task_lists opts ] ++
+         [ (wikilinksSpec TitleAfterPipe <>)
+           | isEnabled Ext_wikilinks_title_after_pipe opts ] ++
+         [ (wikilinksSpec TitleBeforePipe <>)
+           | isEnabled Ext_wikilinks_title_before_pipe opts ] ++
          [ (rebaseRelativePathsSpec <>)
            | isEnabled Ext_rebase_relative_paths opts ]
-

src/Text/Pandoc/Writers/Markdown/Inline.hs

@@ -545,6 +545,7 @@ inlineToMarkdown opts lnk@(Link attr@(ident,classes,kvs) txt (src, tit)) = do
                 case txt of
                       [Str s] | escapeURI s == srcSuffix -> True
                       _       -> False
+  let useWikilink = tit == "wikilink"
   let useRefLinks = writerReferenceLinks opts && not useAuto
   shortcutable <- asks envRefShortcutable
   let useShortcutRefLinks = shortcutable &&
@@ -557,6 +558,11 @@ inlineToMarkdown opts lnk@(Link attr@(ident,classes,kvs) txt (src, tit)) = do
       | useAuto -> return $ literal srcSuffix
       | otherwise -> return linktext
     _ | useAuto -> return $ "<" <> literal srcSuffix <> ">"
+      | useAuto && useWikilink -> return $ "[[" <> literal srcSuffix <> "]]"
+      | useWikilink && isEnabled Ext_wikilinks_title_after_pipe opts -> return $
+        "[[" <> literal src <> "|" <> linktext <> "]]"
+      | useWikilink && isEnabled Ext_wikilinks_title_before_pipe opts -> return $
+        "[[" <> linktext <> "|" <> literal src <> "]]"
       | useRefLinks ->
            let first  = "[" <> linktext <> "]"
                second = if getKey linktext == getKey reftext

test/command/wikilinks_title_after_pipe.md

@@ -0,0 +1,16 @@
+```
+% pandoc --from commonmark_x+wikilinks_title_after_pipe -t html
+[[https://example.org]]
+
+[[https://example.org|title]]
+
+[[name of page]]
+
+[[name of page|title]]
+^D
+<p><a href="https://example.org" title="wikilink">https://example.org</a></p>
+<p><a href="https://example.org" title="wikilink">title</a></p>
+<p><a href="name of page" title="wikilink">name of page</a></p>
+<p><a href="name of page" title="wikilink">title</a></p>
+```
+

test/command/wikilinks_title_before_pipe.md

@@ -0,0 +1,26 @@
+```
+% pandoc -f commonmark+wikilinks_title_before_pipe -t html
+[[https://example.org]]
+
+[[title|https://example.org]]
+
+[[Name of page]]
+
+[[Title|Name of page]]
+^D
+<p><a href="https://example.org" title="wikilink">https://example.org</a></p>
+<p><a href="https://example.org" title="wikilink">title</a></p>
+<p><a href="Name of page" title="wikilink">Name of page</a></p>
+<p><a href="Name of page" title="wikilink">Title</a></p>
+```
+
+# Regular links should still work
+
+```
+% pandoc -f commonmark+wikilinks_title_before_pipe -t html
+[Title](Name%20of%20page)
+^D
+<p><a href="Name%20of%20page">Title</a></p>
+```
+
+