Consistently use the Cabal version picked by the dependency solver.

Previously, cabal always chose a Cabal library version to use for a package's
setup script that didn't take setup-depends into account (cabalLibVersion).
cabalLibVersion depended on the cabal-version field, the installed versions of
Cabal, etc., and it was used when setup dependencies were not chosen by the
dependency solver. When a package had a setup-depends, cabalLibVersion was later
ignored in favor of the version chosen by the dependency solver. However,
calculating the variable caused an error when the only suitable Cabal version
was installed during the same install command (issue haskell#3436). cabalLibVersion was
also used to filter the configure flags (issue haskell#3433).

This commit sets cabalLibVersion to the version chosen by the dependency solver,
when possible.

cabal-install/Distribution/Client/SetupWrapper.hs

@@ -106,7 +106,7 @@ import Control.Applicative ( (<$>), (<*>) )
 import Data.Monoid         ( mempty )
 #endif
 import Control.Monad       ( when, unless )
-import Data.List           ( foldl1' )
+import Data.List           ( find, foldl1' )
 import Data.Maybe          ( fromMaybe, isJust )
 import Data.Char           ( isSpace )
 import Distribution.Client.Compat.ExecutablePath  ( getExecutablePath )
@@ -389,26 +389,33 @@ externalSetupMethod verbosity options pkg bt mkargs = do
       Nothing    -> getInstalledPackages verbosity
                     comp (usePackageDB options') conf
 
-  cabalLibVersionToUse :: IO (Version, (Maybe ComponentId)
+  cabalLibVersionToUse :: IO (Version, Maybe ComponentId
                              ,SetupScriptOptions)
   cabalLibVersionToUse =
-    case useCabalSpecVersion options of
-      Just version -> do
+    case find (hasCabal . snd) (useDependencies options) of
+      Just (unitId, pkgId) -> do
+        let version = pkgVersion pkgId
         updateSetupScript version bt
-        writeFile setupVersionFile (show version ++ "\n")
-        return (version, Nothing, options)
-      Nothing  -> do
-        savedVer <- savedVersion
-        case savedVer of
-          Just version | version `withinRange` useCabalVersion options
-            -> do updateSetupScript version bt
-                  -- Does the previously compiled setup executable still exist
-                  -- and is it up-to date?
-                  useExisting <- canUseExistingSetup version
-                  if useExisting
-                    then return (version, Nothing, options)
-                    else installedVersion
-          _ -> installedVersion
+        writeSetupVersionFile version
+        return (version, Just unitId, options)
+      Nothing ->
+        case useCabalSpecVersion options of
+          Just version -> do
+            updateSetupScript version bt
+            writeSetupVersionFile version
+            return (version, Nothing, options)
+          Nothing  -> do
+            savedVer <- savedVersion
+            case savedVer of
+              Just version | version `withinRange` useCabalVersion options
+                -> do updateSetupScript version bt
+                      -- Does the previously compiled setup executable still exist
+                      -- and is it up-to date?
+                      useExisting <- canUseExistingSetup version
+                      if useExisting
+                        then return (version, Nothing, options)
+                        else installedVersion
+              _ -> installedVersion
     where
       -- This check duplicates the checks in 'getCachedSetupExecutable' /
       -- 'compileSetupExecutable'. Unfortunately, we have to perform it twice
@@ -424,13 +431,20 @@ externalSetupMethod verbosity options pkg bt mkargs = do
           (&&) <$> setupProgFile `existsAndIsMoreRecentThan` setupHs
                <*> setupProgFile `existsAndIsMoreRecentThan` setupVersionFile
 
+      writeSetupVersionFile :: Version -> IO ()
+      writeSetupVersionFile version =
+          writeFile setupVersionFile (show version ++ "\n")
+
+      hasCabal (PackageIdentifier (PackageName "Cabal") _) = True
+      hasCabal _                                           = False
+
       installedVersion :: IO (Version, Maybe InstalledPackageId
                              ,SetupScriptOptions)
       installedVersion = do
         (comp,    conf,    options')  <- configureCompiler options
         (version, mipkgid, options'') <- installedCabalVersion options' comp conf
         updateSetupScript version bt
-        writeFile setupVersionFile (show version ++ "\n")
+        writeSetupVersionFile version
         return (version, mipkgid, options'')
 
       savedVersion :: IO (Maybe Version)