Resolve #100. XDG paths have to be absolute

Morally revert b9d0d69

CONTRIBUTING.md

@@ -0,0 +1,3 @@
+Contributions and bug reports are welcome!
+
+Please remember to add changelog entries.

System/Directory.hs

@@ -1532,8 +1532,8 @@ getXdgDirectory xdgDir suffix =
         XdgConfig -> "XDG_CONFIG_HOME"
         XdgCache  -> "XDG_CACHE_HOME"
       case env of
-        Nothing   -> getXdgDirectoryFallback getHomeDirectory xdgDir
-        Just path -> pure path
+        Just path | isAbsolute path -> pure path
+        _                           -> getXdgDirectoryFallback getHomeDirectory xdgDir
 
 -- | Similar to 'getXdgDirectory' but retrieves the entire list of XDG
 -- directories.

changelog.md

@@ -1,6 +1,14 @@
 Changelog for the [`directory`][1] package
 ==========================================
 
+## 1.3.5.0 (December 2019)
+
+  * Revert change introduced in the version `1.3.2.2`:
+    Non-absolute `XDG_*` environment variables are ignored.
+    This behavior is according to *XDG Base Directory Specification*
+    version 0.7, https://specifications.freedesktop.org/basedir-spec/0.7/ar01s02.html
+    ([#100](https://github.com/haskell/directory/issues/100))
+
 ## 1.3.4.0 (July 2019)
 
   * `getXdgDirectory` and `getXdgDirectoryList` on Windows will now respect

directory.cabal

@@ -1,6 +1,5 @@
 name:           directory
-version:        1.3.4.0
--- NOTE: Don't forget to update ./changelog.md
+version:        1.3.5.0
 license:        BSD3
 license-file:   LICENSE
 maintainer:     libraries@haskell.org

tests/Xdg.hs

@@ -3,7 +3,10 @@ module Xdg where
 #if MIN_VERSION_base(4, 7, 0)
 import qualified Data.List as List
 import System.Environment (setEnv, unsetEnv)
-import System.FilePath ((</>), searchPathSeparator)
+import System.FilePath (searchPathSeparator)
+#if !defined(mingw32_HOST_OS)
+import System.FilePath ((</>))
+#endif
 #endif
 #include "util.inl"
 
@@ -24,12 +27,21 @@ main _t = do
   T(expectEq) () (home </> ".config/mow") =<< getXdgDirectory XdgConfig "mow"
 #endif
 
+  -- unset variables, so env doesn't affect test running
+  unsetEnv "XDG_DATA_HOME"
+  unsetEnv "XDG_CONFIG_HOME"
+  unsetEnv "XDG_CACHE_HOME"
+  xdgData   <- getXdgDirectory XdgData   "ff"
+  xdgConfig <- getXdgDirectory XdgConfig "oo"
+  xdgCache  <- getXdgDirectory XdgCache  "rk"
+
+  -- non-absolute paths are ignored, and the fallback is used
   setEnv "XDG_DATA_HOME"   "ar"
   setEnv "XDG_CONFIG_HOME" "aw"
   setEnv "XDG_CACHE_HOME"  "ba"
-  T(expectEq) () ("ar" </> "ff") =<< getXdgDirectory XdgData   "ff"
-  T(expectEq) () ("aw" </> "oo") =<< getXdgDirectory XdgConfig "oo"
-  T(expectEq) () ("ba" </> "rk") =<< getXdgDirectory XdgCache  "rk"
+  T(expectEq) () xdgData   =<< getXdgDirectory XdgData   "ff"
+  T(expectEq) () xdgConfig =<< getXdgDirectory XdgConfig "oo"
+  T(expectEq) () xdgCache  =<< getXdgDirectory XdgCache  "rk"
 
   unsetEnv "XDG_CONFIG_DIRS"
   unsetEnv "XDG_DATA_DIRS"