add compiler info to --version

I'm not sure if this counts as a significant change or not, since
it's possible scripts depend on the output. (The git info change
doesn't really count, since it's only operable on unreleased
versions.)

Author: geekosaur

cabal-install/cabal-install.cabal

@@ -132,6 +132,7 @@ library
         Distribution.Client.Compat.Orphans
         Distribution.Client.Compat.Prelude
         Distribution.Client.Compat.Semaphore
+        Distribution.Client.Compat.SysInfo
         Distribution.Client.Compat.Tar
         Distribution.Client.Config
         Distribution.Client.Configure

cabal-install/src/Distribution/Client/Compat/SysInfo.hs

@@ -0,0 +1,15 @@
+{-# LANGUAGE CPP #-}
+
+module Distribution.Compat.SysInfo
+  ( fullCompilerVersion
+  ) where
+
+import Data.Version
+import qualified System.Info as SI
+
+fullCompilerVersion :: Version
+#if MIN_VERSION_base(4,15,0)
+fullCompilerVersion = SI.fullCompilerVersion
+#else
+fullCompilerVersion = SI.compilerVersion
+#endif

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

@@ -170,7 +170,8 @@ import Distribution.Client.Utils
   , relaxEncodingErrors
   )
 import Distribution.Client.Version
-  ( cabalInstallGitInfo
+  ( cabalInstallCompilerInfo
+  , cabalInstallGitInfo
   , cabalInstallVersion
   )
 
@@ -424,6 +425,8 @@ mainWorker args = do
           ++ display cabalVersion
           ++ " of the Cabal library "
           ++ cabalGitInfo'
+          ++ "\nwith "
+          ++ cabalInstallCompilerInfo
       where
         cabalGitInfo'
           | cabalGitInfo == cabalInstallGitInfo = "(in-tree)"

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

@@ -7,9 +7,14 @@
 module Distribution.Client.Version
   ( cabalInstallVersion
   , cabalInstallGitInfo
+  , cabalInstallCompilerInfo
   ) where
 
+import Data.List (intercalate)
+import qualified Data.Version as DV
 import Distribution.Version
+import qualified System.Info as SI
+import qualified Distribution.Client.Compat.SysInfo as SIC
 
 import qualified Paths_cabal_install as PackageInfo
 
@@ -28,6 +33,21 @@ import GitHash
 cabalInstallVersion :: Version
 cabalInstallVersion = mkVersion' PackageInfo.version
 
+{- FOURMOLU_DISABLE -}
+-- |
+-- `cabal-install` compiler information.
+cabalInstallCompilerInfo :: String
+cabalInstallCompilerInfo = let ci = SIC.fullCompilerVersion
+                              in concat [ SI.compilerName
+                                        , " "
+                                        , intercalate "." (map show (DV.versionBranch ci))
+                                        , " on "
+                                        , SI.os
+                                        , " "
+                                        , SI.arch
+                                        ]
+{- FOURMOLU_ENABLE -}
+
 -- |
 -- `cabal-install` Git information. Only filled in if built in a Git tree in
 -- developmnent mode and Template Haskell is available.