Shared: Change defaultUserDataDirs -> defaultUserDataDir.

Rationale: the manual says that the XDG data directory will
be used if it exists, otherwise the legacy data directory.
So we should just determine this and use this directory,
rather than having a search path which could cause some
things to be taken from one data directory and others from
others.

[API change]

1 files changed, 12 insertions, 8 deletions

diff --git a/src/Text/Pandoc/Shared.hs b/src/Text/Pandoc/Shared.hs
index 922df7922..2aba9b2e1 100644
--- a/src/Text/Pandoc/Shared.hs
+++ b/src/Text/Pandoc/Shared.hs
@@ -95,7 +95,7 @@ module Text.Pandoc.Shared (
                      safeRead,
                      safeStrRead,
                      -- * User data directory
-                     defaultUserDataDirs,
+                     defaultUserDataDir,
                      -- * Version
                      pandocVersion
                     ) where
@@ -1012,12 +1012,16 @@ safeStrRead s = case reads s of
 --
 
 -- | Return appropriate user data directory for platform.  We use
--- XDG_DATA_HOME (or its default value), but fall back to the
--- legacy user data directory ($HOME/.pandoc on *nix) if this is
--- missing.
-defaultUserDataDirs :: IO [FilePath]
-defaultUserDataDirs = E.catch (do
+-- XDG_DATA_HOME (or its default value), but for backwards compatibility,
+-- we fall back to the legacy user data directory ($HOME/.pandoc on *nix)
+-- if the XDG_DATA_HOME is missing and this exists.  If neither directory
+-- is present, we return the XDG data directory.
+defaultUserDataDir :: IO FilePath
+defaultUserDataDir = do
   xdgDir <- getXdgDirectory XdgData "pandoc"
   legacyDir <- getAppUserDataDirectory "pandoc"
-  return $ ordNub [xdgDir, legacyDir])
- (\(_ :: E.SomeException) -> return [])
+  xdgExists <- doesDirectoryExist xdgDir
+  legacyDirExists <- doesDirectoryExist legacyDir
+  if not xdgExists && legacyDirExists
+     then return legacyDir
+     else return xdgDir