Logging: Added UnknownExtensions constructor to LogMessage.

[API change]

Issue this warning when we're falling back to markdown or
html because we don't recognize the extension of the input or
output files.

1 files changed, 9 insertions, 3 deletions

diff --git a/src/Text/Pandoc/App/OutputSettings.hs b/src/Text/Pandoc/App/OutputSettings.hs
index a9034d6f2..31bd64c4c 100644
--- a/src/Text/Pandoc/App/OutputSettings.hs
+++ b/src/Text/Pandoc/App/OutputSettings.hs
@@ -70,9 +70,15 @@ optToOutputSettings opts = do
     if pdfOutput
        then liftIO $ pdfWriterAndProg (optWriter opts) (optPdfEngine opts)
        else case optWriter opts of
-              Nothing  ->
-                return (fromMaybe "html" $ formatFromFilePaths [outputFile],
-                        Nothing)
+              Nothing
+                | outputFile == "-" -> return ("html", Nothing)
+                | otherwise ->
+                    case formatFromFilePaths [outputFile] of
+                           Nothing -> do
+                             report $ UnknownExtensions
+                                [takeExtension outputFile] "html"
+                             return ("html", Nothing)
+                           Just f  -> return (f, Nothing)
               Just f   -> return (f, Nothing)
 
   let format = if ".lua" `isSuffixOf` writerName