Use XDG data directory for user data directory.

Instead of `$HOME/.pandoc`, the default user data directory is
now `$XDG_DATA_HOME/pandoc`, where `XDG_DATA_HOME` defaults to
`$HOME/.local/share` but can be overridden by setting the environment
variable.

If this directory is missing, then `$HOME/.pandoc` is searched
instead, for backwards compatibility.  However, we recommend
moving local pandoc data files from `$HOME/.pandoc` to
`$HOME/.local/share/pandoc`.

On Windows the default user data directory remains the same.

Closes #3582.

2 files changed, 17 insertions, 15 deletions

diff --git a/src/Text/Pandoc/App.hs b/src/Text/Pandoc/App.hs
index 6718617e1..b0527cd79 100644
--- a/src/Text/Pandoc/App.hs
+++ b/src/Text/Pandoc/App.hs
@@ -38,7 +38,7 @@ import qualified Data.Text.Lazy.Encoding as TE
 import qualified Data.Text.Encoding.Error as TE
 import qualified Data.Text.Encoding.Error as TSE
 import Network.URI (URI (..), parseURI)
-import System.Directory (getAppUserDataDirectory)
+import System.Directory (doesDirectoryExist)
 import System.Exit (exitSuccess)
 import System.FilePath
 import System.IO (nativeNewline, stdout)
@@ -55,7 +55,8 @@ import Text.Pandoc.PDF (makePDF)
 import Text.Pandoc.Readers.Markdown (yamlToMeta)
 import Text.Pandoc.SelfContained (makeDataURI, makeSelfContained)
 import Text.Pandoc.Shared (eastAsianLineBreakFilter, stripEmptyParagraphs,
-         headerShift, isURI, tabFilter, uriPathToPath, filterIpynbOutput)
+         headerShift, isURI, tabFilter, uriPathToPath, filterIpynbOutput,
+         defaultUserDataDirs)
 import qualified Text.Pandoc.UTF8 as UTF8
 #ifndef _WINDOWS
 import System.Posix.IO (stdOutput)
@@ -89,10 +90,15 @@ convertWithOpts opts = do
                         | otherwise  -> xs
 
   datadir <- case optDataDir opts of
-                  Nothing   -> E.catch
-                                 (Just <$> getAppUserDataDirectory "pandoc")
-                                 (\e -> let _ = (e :: E.SomeException)
-                                        in  return Nothing)
+                  Nothing   -> do
+                    ds <- defaultUserDataDirs
+                    let selectUserDataDir [] = return Nothing
+                        selectUserDataDir (dir:dirs) = do
+                              exists <- doesDirectoryExist dir
+                              if exists
+                                 then return (Just dir)
+                                 else selectUserDataDir dirs
+                    selectUserDataDir ds
                   Just _    -> return $ optDataDir opts
 
   -- assign reader and writer based on options and filenames
diff --git a/src/Text/Pandoc/App/CommandLineOptions.hs b/src/Text/Pandoc/App/CommandLineOptions.hs
index 7f05418d9..36c68057c 100644
--- a/src/Text/Pandoc/App/CommandLineOptions.hs
+++ b/src/Text/Pandoc/App/CommandLineOptions.hs
@@ -46,15 +46,14 @@ import Text.Pandoc.App.Opt (Opt (..), LineEnding (..))
 import Text.Pandoc.Filter (Filter (..))
 import Text.Pandoc.Highlighting (highlightingStyles)
 import Text.Pandoc.Writers.Math (defaultMathJaxURL, defaultKaTeXURL)
-import Text.Pandoc.Shared (ordNub, safeRead)
+import Text.Pandoc.Shared (ordNub, safeRead, defaultUserDataDirs)
 import Text.Printf
 
 #ifdef EMBED_DATA_FILES
 import Text.Pandoc.Data (dataFiles)
-import System.Directory (getAppUserDataDirectory)
 #else
 import Paths_pandoc (getDataDir)
-import System.Directory (getAppUserDataDirectory, getDirectoryContents)
+import System.Directory (getDirectoryContents)
 #endif
 
 import qualified Control.Exception as E
@@ -837,13 +836,11 @@ options =
                  (NoArg
                   (\_ -> do
                      prg <- getProgName
-                     defaultDatadir <- E.catch
-                            (getAppUserDataDirectory "pandoc")
-                            (\e -> let _ = (e :: E.SomeException)
-                                   in  return "")
+                     defaultDatadirs <- defaultUserDataDirs
                      UTF8.hPutStrLn stdout (prg ++ " " ++ pandocVersion ++
                        compileInfo ++ "\nDefault user data directory: " ++
-                       defaultDatadir ++ copyrightMessage)
+                       intercalate " or " defaultDatadirs ++
+                       ('\n':copyrightMessage))
                      exitSuccess ))
                  "" -- "Print version"
 
@@ -872,7 +869,6 @@ usageMessage programName = usageInfo (programName ++ " [OPTIONS] [FILES]")
 
 copyrightMessage :: String
 copyrightMessage = intercalate "\n" [
-  "",
   "Copyright (C) 2006-2019 John MacFarlane",
   "Web:  http://pandoc.org",
   "This is free software; see the source for copying conditions.",