haskell: allow separate bin output, disable by default

pkgs/development/haskell-modules/generic-builder.nix

@@ -73,6 +73,7 @@ in
 , coreSetup ? false # Use only core packages to build Setup.hs.
 , useCpphs ? false
 , hardeningDisable ? stdenv.lib.optional (ghc.isHaLVM or false) "all"
+, enableSeparateBinOutput ? false
 , enableSeparateDataOutput ? false
 , enableSeparateDocOutput ? doHaddock
 , # Don't fail at configure time if there are multiple versions of the
@@ -111,6 +112,8 @@ let
   # the target dir for haddock documentation
   docdir = docoutput: docoutput + "/share/doc/" + pname + "-" + version;
 
+  binDir = if enableSeparateBinOutput then "$bin/bin" else "$out/bin";
+
   newCabalFileUrl = "http://hackage.haskell.org/package/${pname}-${version}/revision/${revision}.cabal";
   newCabalFile = fetchurl {
     url = newCabalFileUrl;
@@ -143,7 +146,10 @@ let
   buildFlagsString = optionalString (buildFlags != []) (" " + concatStringsSep " " buildFlags);
 
   defaultConfigureFlags = [
-    "--verbose" "--prefix=$out" "--libdir=\\$prefix/lib/\\$compiler" "--libsubdir=\\$abi/\\$libname"
+    "--verbose"
+    "--prefix=$out"
+    "--libdir=\\$prefix/lib/\\$compiler"
+    "--libsubdir=\\$abi/\\$libname"
     (optionalString enableSeparateDataOutput "--datadir=$data/share/${ghc.name}")
     (optionalString enableSeparateDocOutput "--docdir=${docdir "$doc"}")
     "--with-gcc=$CC" # Clang won't work without that extra information.
@@ -173,7 +179,8 @@ let
     "--ghcjs"
   ] ++ optionals isCross ([
     "--configure-option=--host=${stdenv.hostPlatform.config}"
-  ] ++ crossCabalFlags);
+  ] ++ crossCabalFlags
+  ) ++ optionals enableSeparateBinOutput ["--bindir=${binDir}"];
 
   setupCompileFlags = [
     (optionalString (!coreSetup) "-${nativePackageDbFlag}=$setupPackageConfDir")
@@ -233,7 +240,10 @@ assert allPkgconfigDepends != [] -> pkgconfig != null;
 stdenv.mkDerivation ({
   name = "${pname}-${version}";
 
-  outputs = [ "out" ] ++ (optional enableSeparateDataOutput "data") ++ (optional enableSeparateDocOutput "doc");
+  outputs = [ "out" ]
+         ++ (optional enableSeparateDataOutput "data")
+         ++ (optional enableSeparateDocOutput "doc")
+         ++ (optional enableSeparateBinOutput "bin");
   setOutputFlags = false;
 
   pos = builtins.unsafeGetAttrPos "pname" args;
@@ -414,7 +424,7 @@ stdenv.mkDerivation ({
       find $packageConfDir -maxdepth 0 -empty -delete;
     ''}
     ${optionalString isGhcjs ''
-      for exeDir in "$out/bin/"*.jsexe; do
+      for exeDir in "${binDir}/"*.jsexe; do
         exe="''${exeDir%.jsexe}"
         printWords '#!${nodejs}/bin/node' > "$exe"
         echo >> "$exe"
@@ -424,7 +434,7 @@ stdenv.mkDerivation ({
     ''}
     ${optionalString doCoverage "mkdir -p $out/share && cp -r dist/hpc $out/share"}
     ${optionalString (enableSharedExecutables && isExecutable && !isGhcjs && stdenv.isDarwin && stdenv.lib.versionOlder ghc.version "7.10") ''
-      for exe in "$out/bin/"* ; do
+      for exe in "${binDir}/"* ; do
         install_name_tool -add_rpath "$out/lib/ghc-${ghc.version}/${pname}-${version}" "$exe"
       done
     ''}

pkgs/development/haskell-modules/lib.nix

@@ -181,6 +181,8 @@ rec {
   enableStaticLibraries = drv: overrideCabal drv (drv: { enableStaticLibraries = true; });
   disableStaticLibraries = drv: overrideCabal drv (drv: { enableStaticLibraries = false; });
 
+  enableSeparateBinOutput = drv: overrideCabal drv (drv: { enableSeparateBinOutput = true; });
+
   appendPatch = drv: x: appendPatches drv [x];
   appendPatches = drv: xs: overrideCabal drv (drv: { patches = (drv.patches or []) ++ xs; });