haskell-packages.nix: fix the implementation of 'cabalNoTest'

The previous implementation used the following tying-the-knot trickery to
override 'doCheck' to false for the given build:

  cabalNoTest = {
    mkDerivation = x: rec {
      final = self.cabal.mkDerivation (self: (x final) // { doCheck = false; });
    }.final;
  };

That seemed to work, but for some reason it caused trouble with some builds --
not all -- that use jailbreakCabal. The problem was the 'stdenv' attribute
couldn't be evaluated properly anymore:

  $ nix-build ~/pkgs/top-level/release-haskell.nix -A optparseApplicative.ghc6104.x86_64-linux --show-trace
  error: while evaluating the attribute `drvPath' at `/nix/store/qkj5cxknwspz8ak0ganm97zfr2bhksgn-nix-1.5.2pre3082_2398417/share/nix/corepkgs/derivation.nix:19:9':
  while evaluating the builtin function `derivationStrict':
  while instantiating the derivation named `haskell-optparse-applicative-ghc6.10.4-0.5.2.1' at `/home/simons/.nix-defexpr/pkgs/build-support/cabal/default.nix:40:13':
  while evaluating the derivation attribute `configurePhase' at `/home/simons/.nix-defexpr/pkgs/build-support/cabal/default.nix:107:13':
  while evaluating the function at `/home/simons/.nix-defexpr/pkgs/lib/strings.nix:55:26':
  while evaluating the attribute `outPath' at `/nix/store/qkj5cxknwspz8ak0ganm97zfr2bhksgn-nix-1.5.2pre3082_2398417/share/nix/corepkgs/derivation.nix:18:9':
  while evaluating the builtin function `getAttr':
  while evaluating the builtin function `derivationStrict':
  while instantiating the derivation named `jailbreak-cabal-1.1' at `/home/simons/.nix-defexpr/pkgs/build-support/cabal/default.nix:40:13':
  while evaluating the derivation attribute `nativeBuildInputs' at `/home/simons/.nix-defexpr/pkgs/stdenv/generic/default.nix:76:17':
  while evaluating the function at `/home/simons/.nix-defexpr/pkgs/lib/lists.nix:135:21':
  while evaluating the attribute `buildInputs' at `/home/simons/.nix-defexpr/pkgs/build-support/cabal/default.nix:22:17':
  while evaluating the builtin function `filter':
  while evaluating the function at `/home/simons/.nix-defexpr/pkgs/build-support/cabal/default.nix:22:60':
  while evaluating the function at `/home/simons/.nix-defexpr/pkgs/top-level/haskell-packages.nix:119:17':
  while evaluating the function at `/home/simons/.nix-defexpr/pkgs/lib/customisation.nix:61:22':
  while evaluating the function at `/home/simons/.nix-defexpr/pkgs/lib/customisation.nix:56:24':
  while evaluating the builtin function `isAttrs':
  while evaluating the function at `/home/simons/.nix-defexpr/pkgs/development/libraries/haskell/Cabal/1.14.0.nix:1:1':
  while evaluating the function at `/home/simons/.nix-defexpr/pkgs/top-level/haskell-packages.nix:113:20':
  while evaluating the attribute `final' at `/home/simons/.nix-defexpr/pkgs/top-level/haskell-packages.nix:114:7':
  while evaluating the function at `/home/simons/.nix-defexpr/pkgs/build-support/cabal/default.nix:9:5':
  while evaluating the function at `/home/simons/.nix-defexpr/pkgs/stdenv/generic/default.nix:51:24':
  while evaluating the attribute `meta.license' at `/home/simons/.nix-defexpr/pkgs/development/libraries/haskell/Cabal/1.14.0.nix:17:5':
  infinite recursion encountered

I tried to figure out why this happens, but eventually gave up. The new
implementation passes an argument called 'enableCheckPhase' to the Cabal
builder, which determines whether the user-specified doCheck value has any
effect or not. Now, a normal override can be used to disable unit testing.

pkgs/build-support/cabal/default.nix

@@ -1,6 +1,13 @@
 # generic builder for Cabal packages
 
-{ stdenv, fetchurl, lib, pkgconfig, ghc, Cabal, jailbreakCabal, enableLibraryProfiling ? false }:
+{ stdenv, fetchurl, lib, pkgconfig, ghc, Cabal, jailbreakCabal
+, enableLibraryProfiling ? false
+, enableCheckPhase ? true
+}:
+
+# 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;
+
 {
   mkDerivation =
     args : # arguments for the individual package, can modify the defaults
@@ -18,6 +25,7 @@
           x : (removeAttrs x internalAttrs) // {
                 buildInputs           = stdenv.lib.filter (y : ! (y == null)) x.buildInputs;
                 propagatedBuildInputs = stdenv.lib.filter (y : ! (y == null)) x.propagatedBuildInputs;
+                doCheck               = enableCheckPhase && x.doCheck;
               };
 
         defaults =
@@ -92,7 +100,7 @@
 
             # pass the '--enable-tests' flag to cabal in the configure stage
             # and run any regression test suites the package might have
-            doCheck = stdenv.lib.versionOlder "7.4" ghc.ghcVersion;
+            doCheck = enableCheckPhase;
 
             extraConfigureFlags = [
               (stdenv.lib.enableFeature enableLibraryProfiling "library-profiling")

pkgs/top-level/haskell-packages.nix

@@ -104,16 +104,13 @@ let result = let callPackage = x : y : modifyPrio (newScope result.final x y);
 
   cabal = callPackage ../build-support/cabal {
     enableLibraryProfiling = enableLibraryProfiling;
+    enableCheckPhase = pkgs.stdenv.lib.versionOlder "7.4" self.ghc.ghcVersion;
   };
 
   # A variant of the cabal build driver that disables unit testing.
   # Useful for breaking cycles, where the unit test of a package A
   # depends on package B, which has A as a regular build input.
-  cabalNoTest = {
+  cabalNoTest = self.cabal.override { enableCheckPhase = false; };
-    mkDerivation = x: rec {
-      final = self.cabal.mkDerivation (self: (x final) // { doCheck = false; });
-    }.final;
-  };
 
   # Convenience helper function.
   disableTest = x: x.override { cabal = self.cabalNoTest; };