Lookup PAGER env var (#1)

Also: Fix color formatting when PAGER is 'less'

Author: hasufell

cabal-install/src/Distribution/Client/Manpage.hs

@@ -34,6 +34,8 @@ import Distribution.Simple.Utils
   ( IOData(..), IODataMode(..), createProcessWithEnv, ignoreSigPipe, rawSystemStdInOut )
 import qualified Distribution.Verbosity as Verbosity
 import System.IO                        (hClose, hPutStr)
+import System.Environment               (lookupEnv)
+import System.FilePath                  (takeFileName)
 
 import qualified System.Process as Process
 
@@ -78,11 +80,14 @@ manpageCmd pname commands flags
 
         unless (ec1 == ExitSuccess) $ exitWith ec1
 
+        pager <- fromMaybe "less" <$> lookupEnv "PAGER"
+        -- 'less' is borked with color sequences otherwise
+        let pagerArgs = if takeFileName pager == "less" then ["-R"] else []
         -- Pipe output of @nroff@ into @less@
         (Just inLess, _, _, procLess) <- createProcessWithEnv
           Verbosity.normal
-          "less"
-          []
+          pager
+          pagerArgs
           Nothing  -- Inherit working directory
           Nothing  -- Inherit environment
           Process.CreatePipe  -- in