Improve text generated for <xref> by employing docbook-xsl heuristics

docbook-xsl, a set of XSLT scripts to generate HMTL out of DocBook,
tries harder to generate a nice xref text. Depending on the element
being linked to, it looks at the title or other descriptive child
elements. Let's do that, too.

2 files changed, 19 insertions, 5 deletions

diff --git a/src/Text/Pandoc/Readers/DocBook.hs b/src/Text/Pandoc/Readers/DocBook.hs
index 164b44b62..9243221f0 100644
--- a/src/Text/Pandoc/Readers/DocBook.hs
+++ b/src/Text/Pandoc/Readers/DocBook.hs
@@ -1024,8 +1024,22 @@ parseInline (Elem e) =
          findElementById idString content
             = asum [filterElement (\x -> attrValue "id" x == idString) el | Elem el <- content]
 
+         -- Use the 'xreflabel' attribute for getting the title of a xref link;
+         -- if there's no such attribute, employ some heuristics based on what
+         -- docbook-xsl does.
          xrefTitleByElem el
-             | null xrefLabel = "???"
-             | otherwise      = xrefLabel
+             | not (null xrefLabel) = xrefLabel
+             | otherwise            = case qName (elName el) of
+                  "chapter"      -> descendantContent "title" el
+                  "sect1"        -> descendantContent "title" el
+                  "sect2"        -> descendantContent "title" el
+                  "sect3"        -> descendantContent "title" el
+                  "sect4"        -> descendantContent "title" el
+                  "sect5"        -> descendantContent "title" el
+                  "cmdsynopsis"  -> descendantContent "command" el
+                  "funcsynopsis" -> descendantContent "function" el
+                  _              -> qName (elName el) ++ "_title"
           where
             xrefLabel = attrValue "xreflabel" el
+            descendantContent name = maybe "???" strContent
+                                   . findElement (QName name Nothing Nothing)
diff --git a/tests/docbook-xref.native b/tests/docbook-xref.native
index 70027b2c5..ec870842b 100644
--- a/tests/docbook-xref.native
+++ b/tests/docbook-xref.native
@@ -2,11 +2,11 @@ Pandoc (Meta {unMeta = fromList []})
 [Header 1 ("ch01",[],[]) [Str "XRef",Space,Str "Samples"]
 ,Para [Str "This",Space,Str "paragraph",Space,Str "demonstrates",Space,Str "several",Space,Str "features",Space,Str "of",Space,Str "XRef."]
 ,BulletList
- [[Para [Str "A",Space,Str "straight",Space,Str "link",Space,Str "generates",Space,Str "the",Space,Str "cross-reference",Space,Str "text:",Space,Link [Str "???"] ("#ch02",""),Str "."]]
+ [[Para [Str "A",Space,Str "straight",Space,Str "link",Space,Str "generates",Space,Str "the",Space,Str "cross-reference",Space,Str "text:",Space,Link [Str "The Second Chapter"] ("#ch02",""),Str "."]]
  ,[Para [Str "A",Space,Str "link",Space,Str "to",Space,Str "an",Space,Str "element",Space,Str "with",Space,Str "an",Space,Str "XRefLabel:",Space,Link [Str "Chapter the Third"] ("#ch03",""),Str "."]]
  ,[Para [Str "A",Space,Str "link",Space,Str "with",Space,Str "an",Space,Str "EndTerm:",Space,Link [Str "Chapter 4"] ("#ch04",""),Str "."]]
- ,[Para [Str "A",Space,Str "link",Space,Str "to",Space,Str "an",Space,Str "cmdsynopsis",Space,Str "element:",Space,Link [Str "???"] ("#cmd01",""),Str "."]]
- ,[Para [Str "A",Space,Str "link",Space,Str "to",Space,Str "an",Space,Str "funcsynopsis",Space,Str "element:",Space,Link [Str "???"] ("#func01",""),Str "."]]]
+ ,[Para [Str "A",Space,Str "link",Space,Str "to",Space,Str "an",Space,Str "cmdsynopsis",Space,Str "element:",Space,Link [Str "chgrp"] ("#cmd01",""),Str "."]]
+ ,[Para [Str "A",Space,Str "link",Space,Str "to",Space,Str "an",Space,Str "funcsynopsis",Space,Str "element:",Space,Link [Str "max"] ("#func01",""),Str "."]]]
 ,Header 1 ("ch02",[],[]) [Str "The",Space,Str "Second",Space,Str "Chapter"]
 ,Para [Str "Some",Space,Str "content",Space,Str "here"]
 ,Header 1 ("ch03",[],[]) [Str "The",Space,Str "Third",Space,Str "Chapter"]