pkgs/build-support/cabal: stabilize shared linking support

We cannot pass the --{enable,disable}-executable-dynamic flags to GHC
versions prior to 7.4.x.

Building shared libraries via --{enable,disable}-shared is possible in theory
with GHC 6.12.x or later, but doesn't work in practice because our GHC 6.10.x
builds don't provide shared versions of their base libraries. This could
probably be fixed, but it's probably not worth the effort.

pkgs/build-support/cabal/default.nix

···
 , enableLibraryProfiling ? false
 , enableSharedLibraries ? false
 , enableSharedExecutables ? false
-, enableCheckPhase ? true
+, enableCheckPhase ? stdenv.lib.versionOlder "7.4" ghc.version
 }:
 
-# The Cabal library shipped with GHC versions older than 7.x doesn't accept the --enable-tests configure flag.
-assert enableCheckPhase -> stdenv.lib.versionOlder "7" ghc.ghcVersion;
+let
+  enableFeature         = stdenv.lib.enableFeature;
+  versionOlder          = stdenv.lib.versionOlder;
+  optional              = stdenv.lib.optional;
+  optionals             = stdenv.lib.optionals;
+  optionalString        = stdenv.lib.optionalString;
+  filter                = stdenv.lib.filter;
+in
+
+# Cabal shipped with GHC 6.12.4 or earlier doesn't know the "--enable-tests configure" flag.
+assert enableCheckPhase -> versionOlder "7" ghc.version;
+
+# GHC prior to 7.4.x doesn't know the "--enable-executable-dynamic" flag.
+assert enableSharedExecutables -> versionOlder "7.4" ghc.version;
+
+# Our GHC 6.10.x builds do not provide sharable versions of their core libraries.
+assert enableSharedLibraries -> versionOlder "6.12" ghc.version;
 
 {
   mkDerivation =
···
         # in the interest of keeping hashes stable.
         postprocess =
           x : (removeAttrs x internalAttrs) // {
-                buildInputs           = stdenv.lib.filter (y : ! (y == null)) x.buildInputs;
-                propagatedBuildInputs = stdenv.lib.filter (y : ! (y == null)) x.propagatedBuildInputs;
+                buildInputs           = filter (y : ! (y == null)) x.buildInputs;
+                propagatedBuildInputs = filter (y : ! (y == null)) x.propagatedBuildInputs;
                 doCheck               = enableCheckPhase && x.doCheck;
               };
 
···
             # but often propagatedBuildInputs is preferable anyway
             buildInputs = [ghc Cabal] ++ self.extraBuildInputs;
             extraBuildInputs = self.buildTools ++
-                               (stdenv.lib.optionals self.doCheck self.testDepends) ++
+                               (optionals self.doCheck self.testDepends) ++
                                (if self.pkgconfigDepends == [] then [] else [pkgconfig]) ++
                                (if self.isLibrary then [] else self.buildDepends ++ self.extraLibraries ++ self.pkgconfigDepends);
 
···
             jailbreak = false;
 
             # pass the '--enable-split-objs' flag to cabal in the configure stage
-            enableSplitObjs = !(  stdenv.isDarwin         # http://hackage.haskell.org/trac/ghc/ticket/4013
-                               || stdenv.lib.versionOlder "7.6.99" ghc.ghcVersion  # -fsplit-ojbs is broken in 7.7 snapshot
+            enableSplitObjs = !(  stdenv.isDarwin                       # http://hackage.haskell.org/trac/ghc/ticket/4013
+                               || versionOlder "7.6.99" ghc.version     # -fsplit-ojbs is broken in 7.7 snapshot
                                );
 
             # pass the '--enable-tests' flag to cabal in the configure stage
···
             inherit enableSharedExecutables;
 
             extraConfigureFlags = [
-              (stdenv.lib.enableFeature enableLibraryProfiling "library-profiling")
-              (stdenv.lib.enableFeature self.enableSharedLibraries "shared")
-              (stdenv.lib.enableFeature self.enableSharedExecutables "executable-dynamic")
-              (stdenv.lib.enableFeature self.enableSplitObjs "split-objs")
-            ] ++ stdenv.lib.optional (stdenv.lib.versionOlder "7" ghc.ghcVersion) (stdenv.lib.enableFeature self.doCheck "tests");
+              (enableFeature self.enableSplitObjs "split-objs")
+              (enableFeature enableLibraryProfiling "library-profiling")
+              (enableFeature self.enableSharedLibraries "shared")
+              (optional (versionOlder "7.4" ghc.version) (enableFeature self.enableSharedExecutables "executable-dynamic"))
+              (optional (versionOlder "7" ghc.version) (enableFeature self.doCheck "tests"))
+            ];
 
             # GHC needs the locale configured during the Haddock phase.
             LANG = "en_US.UTF-8";
-            LOCALE_ARCHIVE = lib.optionalString stdenv.isLinux "${glibcLocales}/lib/locale/locale-archive";
+            LOCALE_ARCHIVE = optionalString stdenv.isLinux "${glibcLocales}/lib/locale/locale-archive";
 
             # compiles Setup and configures
             configurePhase = ''
               eval "$preConfigure"
 
-              ${lib.optionalString self.jailbreak "${jailbreakCabal}/bin/jailbreak-cabal ${self.pname}.cabal"}
+              ${optionalString self.jailbreak "${jailbreakCabal}/bin/jailbreak-cabal ${self.pname}.cabal"}
 
               for i in Setup.hs Setup.lhs; do
                 test -f $i && ghc --make $i
···
               eval "$postBuild"
             '';
 
-            checkPhase = stdenv.lib.optional self.doCheck ''
+            checkPhase = optional self.doCheck ''
               eval "$preCheck"
 
               ./Setup test ${self.testTarget}

pkgs/top-level/haskell-packages.nix

···
 #
 # For most packages, however, we keep only one version, and use default.nix.
 
-{pkgs, newScope, ghc, prefFun, enableLibraryProfiling ? false, modifyPrio ? (x : x)}:
+{ pkgs, newScope, ghc, prefFun, modifyPrio ? (x : x)
+, enableLibraryProfiling ? false
+, enableSharedLibraries ? true
+, enableSharedExecutables ? false
+, enableCheckPhase ? pkgs.stdenv.lib.versionOlder "7.4" ghc.version
+}:
 
 # We redefine callPackage to take into account the new scope. The optional
 # modifyPrio argument can be set to lowPrio to make all Haskell packages have
···
   # packages. It isn't the Cabal library, which is spelled "Cabal".
 
   cabal = callPackage ../build-support/cabal {
-    enableLibraryProfiling = enableLibraryProfiling;
-    enableCheckPhase = pkgs.stdenv.lib.versionOlder "7.4" self.ghc.ghcVersion;
+    inherit enableLibraryProfiling;
+    inherit enableSharedLibraries;
+    inherit enableSharedExecutables;
+    inherit enableCheckPhase;
     glibcLocales = if pkgs.stdenv.isLinux then pkgs.glibcLocales else null;
   };