BibTeX writer: use doclayout and doctemplate.

This change allows bibtex/biblatex output to wrap as other
formats do, depending on the settings of `--wrap` and `--columns`.

It also introduces default templates for bibtex and biblatex,
which allow for using the variables `header-include`, `include-before`
or `include-after` (or alternatively the command line options
`--include-in-header`, `--include-before-body`, `--include-after-body`)
to insert content into the generated bibtex/biblatex.

This change requires a change in the return type of the unexported
`T.P.Citeproc.writeBibTeXString` from `Text` to `Doc Text`.

Closes #7068.

1 files changed, 16 insertions, 3 deletions

diff --git a/src/Text/Pandoc/Writers/BibTeX.hs b/src/Text/Pandoc/Writers/BibTeX.hs
index e1cb47ca1..b9ae0c13a 100644
--- a/src/Text/Pandoc/Writers/BibTeX.hs
+++ b/src/Text/Pandoc/Writers/BibTeX.hs
@@ -25,7 +25,11 @@ import Citeproc (parseLang)
 import Text.Pandoc.Class (PandocMonad)
 import Text.Pandoc.Citeproc.BibTeX as BibTeX
 import Text.Pandoc.Citeproc.MetaValue (metaValueToReference)
-import Text.Pandoc.Writers.Shared (lookupMetaString)
+import Text.Pandoc.Writers.Shared (lookupMetaString, defField,
+                                    addVariablesToContext)
+import Text.DocLayout (render, vcat)
+import Text.DocTemplates (Context(..))
+import Text.Pandoc.Templates (renderTemplate)
 
 -- | Write BibTeX based on the references metadata from a Pandoc document.
 writeBibTeX :: PandocMonad m => WriterOptions -> Pandoc -> m Text
@@ -43,6 +47,15 @@ writeBibTeX' variant opts (Pandoc meta _) = do
   let refs = case lookupMeta "references" meta of
                Just (MetaList xs) -> mapMaybe metaValueToReference xs
                _ -> []
-  return $ mconcat $
-    map (BibTeX.writeBibtexString opts variant mblang) refs
+  let main = vcat $ map (BibTeX.writeBibtexString opts variant mblang) refs
+  let context  = defField "body" main
+                 $ addVariablesToContext opts (mempty :: Context Text)
+  let colwidth = if writerWrapText opts == WrapAuto
+                    then Just $ writerColumns opts
+                    else Nothing
+  return $ render colwidth $
+    case writerTemplate opts of
+      Nothing  -> main
+      Just tpl -> renderTemplate tpl context
+