Allow use of ConTeXt to generate PDFs.

pandoc my.md -t context -o my.pdf

will now create a PDF using ConTeXt rather than LaTeX.

Closes #2463.

README

@@ -24,7 +24,7 @@ markup], [Haddock markup], [OPML], [Emacs Org mode], [DocBook],
 [FictionBook2], [Textile], [groff man] pages, [Emacs Org mode],
 [AsciiDoc], [InDesign ICML], and [Slidy], [Slideous], [DZSlides],
 [reveal.js] or [S5] HTML slide shows. It can also produce [PDF] output
-on systems where LaTeX is installed.
+on systems where LaTeX or ConTeXt is installed.
 
 Pandoc's enhanced version of markdown includes syntax for [footnotes],
 [tables], flexible [ordered lists], [definition lists], [fenced code blocks],
@@ -167,7 +167,7 @@ Creating a PDF
 --------------
 
 To produce a PDF, specify an output file with a `.pdf` extension.
-Pandoc will use LaTeX to convert it to PDF:
+By default, pandoc will use LaTeX to convert it to PDF:
 
     pandoc test.txt -o test.pdf
 
@@ -189,7 +189,12 @@ be used for [smart punctuation] if added to the template. The
 optionally be used for [citation rendering]. These are included with
 all recent versions of [TeX Live].
 
-PDF output can be controlled using [variables for LaTeX].
+Alternatively, you can ask pandoc to use ConTeXt to create the PDF.
+To do this, specify an output file with a `.pdf` extension,
+as before, but add `-t context` to the command line.
+
+PDF output can be controlled using [variables for LaTeX]
+or [variables for ConTeXt].
 
 [`amsfonts`]: https://ctan.org/pkg/amsfonts
 [`amsmath`]: https://ctan.org/pkg/amsmath
@@ -992,9 +997,9 @@ customize the `default.opendocument` template.  For `pdf` output,
 customize the `default.latex` template.
 
 Templates contain *variables*, which allow for the inclusion of
-arbitrary information at any point in the file. Variables may be set 
-within the document using [YAML metadata blocks][Extension: `yaml_metadata_block`].
-They may also be set at the
+arbitrary information at any point in the file. Variables may be set
+within the document using [YAML metadata blocks][Extension:
+`yaml_metadata_block`].  They may also be set at the
 command line using the `-V/--variable` option: variables set in this
 way override metadata fields with the same name.
 
@@ -1201,6 +1206,12 @@ LaTeX variables are used when [creating a PDF].
 [`mathpazo`]: https://ctan.org/pkg/mathpazo
 [LaTeX font encodings]: https://ctan.org/pkg/encguide
 
+Variables for ConTeXt
+---------------------
+
+`papersize`
+:   paper size (defaults to `letter`)
+
 Variables for man pages
 -----------------------
 

pandoc.hs

@@ -1173,6 +1173,7 @@ main = do
 
   let laTeXOutput = "latex" `isPrefixOf` writerName' ||
                     "beamer" `isPrefixOf` writerName'
+  let conTeXtOutput = "context" `isPrefixOf` writerName'
 
   writer <- if ".lua" `isSuffixOf` writerName'
                -- note:  use non-lowercased version writerName
@@ -1256,7 +1257,7 @@ main = do
                                 _ -> Nothing
 
   let readerOpts = def{ readerSmart = smart || (texLigatures &&
-                          (laTeXOutput || "context" `isPrefixOf` writerName'))
+                          (laTeXOutput || conTeXtOutput))
                       , readerStandalone = standalone'
                       , readerParseRaw = parseRaw
                       , readerColumns = columns
@@ -1367,17 +1368,20 @@ main = do
     PureStringWriter f
       | pdfOutput -> do
               -- make sure writer is latex or beamer
-              unless laTeXOutput $
+              unless (laTeXOutput || conTeXtOutput) $
                 err 47 $ "cannot produce pdf output with " ++ writerName' ++
                          " writer"
 
+              let texprog = if conTeXtOutput
+                              then "context"
+                              else latexEngine
               -- check for latex program
-              mbLatex <- findExecutable latexEngine
+              mbLatex <- findExecutable texprog
               when (mbLatex == Nothing) $
-                   err 41 $ latexEngine ++ " not found. " ++
-                     latexEngine ++ " is needed for pdf output."
+                   err 41 $ texprog ++ " not found. " ++
+                     texprog ++ " is needed for pdf output."
 
-              res <- makePDF latexEngine f writerOptions doc'
+              res <- makePDF texprog f writerOptions doc'
               case res of
                    Right pdf -> writeBinary pdf
                    Left err' -> do

src/Text/Pandoc/PDF.hs

@@ -47,7 +47,7 @@ import Data.Maybe (fromMaybe)
 import qualified Text.Pandoc.UTF8 as UTF8
 import Text.Pandoc.Definition
 import Text.Pandoc.Walk (walkM)
-import Text.Pandoc.Shared (fetchItem', warn, withTempDir)
+import Text.Pandoc.Shared (fetchItem', warn, withTempDir, inDirectory)
 import Text.Pandoc.Options (WriterOptions(..))
 import Text.Pandoc.MIME (extensionFromMimeType, getMimeType)
 import Text.Pandoc.Process (pipeProcess)
@@ -71,7 +71,9 @@ makePDF program writer opts doc = withTempDir "tex2pdf." $ \tmpdir -> do
   doc' <- handleImages opts tmpdir doc
   let source = writer opts doc'
       args   = writerLaTeXArgs opts
-  tex2pdf' (writerVerbose opts) args tmpdir program source
+  case program of
+     "context" -> context2pdf (writerVerbose opts) tmpdir source
+     _ -> tex2pdf' (writerVerbose opts) args tmpdir program source
 
 handleImages :: WriterOptions
              -> FilePath      -- ^ temp dir to store images
@@ -166,6 +168,14 @@ extractMsg log' = do
      then log'
      else BC.unlines (msg'' ++ lineno)
 
+extractConTeXtMsg :: ByteString -> ByteString
+extractConTeXtMsg log' = do
+  let msg'  = take 1 $
+              dropWhile (not . ("tex error" `BC.isPrefixOf`)) $ BC.lines log'
+  if null msg'
+     then log'
+     else BC.unlines msg'
+
 -- running tex programs
 
 -- Run a TeX program on an input bytestring and return (exit code,
@@ -224,3 +234,55 @@ runTeXProgram verbose program args runNumber numRuns tmpDir source = do
                    else return Nothing
          return (exit, out <> err, pdf)
 
+context2pdf :: Bool         -- ^ Verbose output
+            -> FilePath     -- ^ temp directory for output
+            -> String       -- ^ ConTeXt source
+            -> IO (Either ByteString ByteString)
+context2pdf verbose tmpDir source = inDirectory tmpDir $ do
+  let file = "input.tex"
+  UTF8.writeFile file source
+#ifdef _WINDOWS
+  -- note:  we want / even on Windows, for TexLive
+  let tmpDir' = changePathSeparators tmpDir
+#else
+  let tmpDir' = tmpDir
+#endif
+  let programArgs = ["--batchmode"] ++ [file]
+  env' <- getEnvironment
+  let sep = searchPathSeparator:[]
+  let texinputs = maybe (".." ++ sep) ((".." ++ sep) ++)
+        $ lookup "TEXINPUTS" env'
+  let env'' = ("TEXINPUTS", texinputs) :
+                [(k,v) | (k,v) <- env', k /= "TEXINPUTS"]
+  when verbose $ do
+    putStrLn $ "[makePDF] temp dir:"
+    putStrLn tmpDir'
+    putStrLn $ "[makePDF] Command line:"
+    putStrLn $ "context" ++ " " ++ unwords (map show programArgs)
+    putStr "\n"
+    putStrLn $ "[makePDF] Environment:"
+    mapM_ print env''
+    putStr "\n"
+    putStrLn $ "[makePDF] Contents of " ++ file ++ ":"
+    B.readFile file >>= B.putStr
+    putStr "\n"
+  (exit, out, err) <- pipeProcess (Just env'') "context" programArgs BL.empty
+  when verbose $ do
+    B.hPutStr stdout out
+    B.hPutStr stderr err
+    putStr "\n"
+  let pdfFile = replaceExtension file ".pdf"
+  pdfExists <- doesFileExist pdfFile
+  mbPdf <- if pdfExists
+            -- We read PDF as a strict bytestring to make sure that the
+            -- temp directory is removed on Windows.
+            -- See https://github.com/jgm/pandoc/issues/1192.
+            then (Just . B.fromChunks . (:[])) `fmap` BS.readFile pdfFile
+            else return Nothing
+  let log' = out <> err
+  case (exit, mbPdf) of
+       (ExitFailure _, _)      -> do
+          let logmsg = extractConTeXtMsg log'
+          return $ Left logmsg
+       (ExitSuccess, Nothing)  -> return $ Left ""
+       (ExitSuccess, Just pdf) -> return $ Right pdf