Merge pull request #4193 from ttuegel/nix

Nix integration improvements

Author: ttuegel

Cabal.nix renamed to Cabal/default.nix

@@ -1,20 +1,18 @@
 { mkDerivation, array, base, binary, bytestring, containers
-, deepseq, directory, exceptions, filepath, old-time, pretty
-, process, QuickCheck, regex-posix, stdenv, tagged, tasty
-, tasty-hunit, tasty-quickcheck, time, transformers, unix
+, deepseq, directory, filepath, pretty, process, QuickCheck, stdenv
+, tagged, tasty, tasty-hunit, tasty-quickcheck, time, unix
 }:
 mkDerivation {
   pname = "Cabal";
   version = "1.25.0.0";
-  src = ./Cabal;
+  src = ./.;
   libraryHaskellDepends = [
     array base binary bytestring containers deepseq directory filepath
     pretty process time unix
   ];
   testHaskellDepends = [
-    array base bytestring containers directory exceptions filepath
-    old-time pretty process QuickCheck regex-posix tagged tasty
-    tasty-hunit tasty-quickcheck time transformers unix
+    array base containers directory filepath pretty QuickCheck tagged
+    tasty tasty-hunit tasty-quickcheck
   ];
   doCheck = false;
   homepage = "http://www.haskell.org/cabal/";

Cabal/doc/nix-integration.rst

@@ -12,7 +12,7 @@ To enable Nix integration, simply pass the ``--enable-nix`` global option when y
 
     nix: True
 
-If the package (which must be locally unpacked) provides a ``shell.nix`` file, this flag will cause ``cabal`` to run most commands through ``nix-shell``. The following commands are affected:
+If the package (which must be locally unpacked) provides a ``shell.nix`` or ``default.nix`` file, this flag will cause ``cabal`` to run most commands through ``nix-shell``. If both expressions are present, ``shell.nix`` is preferred. The following commands are affected:
 
 - ``cabal configure``
 - ``cabal build``
@@ -23,7 +23,7 @@ If the package (which must be locally unpacked) provides a ``shell.nix`` file, t
 - ``cabal gen-bounds``
 - ``cabal run``
 
-If the package does not provide a ``shell.nix``, ``cabal`` runs normally.
+If the package does not provide an expression, ``cabal`` runs normally.
 
 Creating Nix Expressions
 ------------------------
@@ -34,6 +34,15 @@ The Nix package manager is based on a lazy, pure, functional programming languag
 
     $ cabal2nix --shell ./. >shell.nix
 
+Nix Expression Evaluation
+-------------------------
+
+(This section describes for advanced users how Nix expressions are evaluated.)
+
+First, the Nix expression (``shell.nix`` or ``default.nix``) is instantiated with ``nix-instantiate``. The ``--add-root`` and ``--indirect`` options are used to create an indirect root in the Cabal build directory, preventing Nix from garbage collecting the derivation while in use. The ``IN_NIX_SHELL`` environment variable is set so that ``builtins.getEnv`` works as it would in ``nix-shell``.
+
+Next, the commands above are run through ``nix-shell`` using the instantiated derivation. Again, ``--add-root`` and ``--indirect`` are used to prevent Nix from garbage collecting the packages in the environment. The child ``cabal`` process reads the ``CABAL_IN_NIX_SHELL`` environment variable to prevent it from spawning additional child shells.
+
 Further Reading
 ----------------
 

cabal-install/Distribution/Client/Nix.hs

@@ -14,18 +14,20 @@ module Distribution.Client.Nix
 import Control.Applicative ((<$>))
 #endif
 
-import Control.Exception (catch)
+import Control.Exception (bracket, catch)
 import Control.Monad (filterM, when, unless)
 import System.Directory
        ( createDirectoryIfMissing, doesDirectoryExist, doesFileExist
        , makeAbsolute, removeDirectoryRecursive, removeFile )
-import System.Environment (getExecutablePath, getArgs, lookupEnv)
+import System.Environment (getArgs, getExecutablePath)
 import System.FilePath
        ( (</>), (<.>), replaceExtension, takeDirectory, takeFileName )
 import System.IO (IOMode(..), hClose, openFile)
 import System.IO.Error (isDoesNotExistError)
 import System.Process (showCommandForUser)
 
+import Distribution.Compat.Environment
+       ( lookupEnv, setEnv, unsetEnv )
 import Distribution.Compat.Semigroup
 
 import Distribution.Verbosity
@@ -70,6 +72,18 @@ findNixExpr globalFlags config = do
     else return Nothing
 
 
+-- set IN_NIX_SHELL so that builtins.getEnv in Nix works as in nix-shell
+inFakeNixShell :: IO a -> IO a
+inFakeNixShell f =
+  bracket (fakeEnv "IN_NIX_SHELL" "1") (resetEnv "IN_NIX_SHELL") (\_ -> f)
+  where
+    fakeEnv var new = do
+      old <- lookupEnv var
+      setEnv var new
+      return old
+    resetEnv var = maybe (unsetEnv var) (setEnv var)
+
+
 nixInstantiate
   :: Verbosity
   -> FilePath
@@ -98,8 +112,9 @@ nixInstantiate verb dist force globalFlags config =
         removeGCRoots verb dist
         touchFile timestamp
 
-        _ <- getDbProgramOutput verb prog progdb
-             [ "--add-root", shellDrv, "--indirect", shellNix ]
+        _ <- inFakeNixShell
+             (getDbProgramOutput verb prog progdb
+              [ "--add-root", shellDrv, "--indirect", shellNix ])
         return ()
 
 
@@ -128,6 +143,9 @@ nixShell verb dist globalFlags config go = do
 
           cabal <- getExecutablePath
 
+          -- alreadyInShell == True in child process
+          setEnv "CABAL_IN_NIX_SHELL" "1"
+
           -- Run cabal with the same arguments inside nix-shell.
           -- When the child process reaches the top of nixShell, it will
           -- detect that it is running inside the shell and fall back
@@ -151,7 +169,7 @@ gcrootPath dist = dist </> "nix" </> "gcroots"
 
 
 inNixShell :: IO Bool
-inNixShell = maybe False (const True) <$> lookupEnv "IN_NIX_SHELL"
+inNixShell = maybe False (const True) <$> lookupEnv "CABAL_IN_NIX_SHELL"
 
 
 removeGCRoots :: Verbosity -> FilePath -> IO ()

cabal-install.nix renamed to cabal-install/default.nix

@@ -1,22 +1,22 @@
 { mkDerivation, array, async, base, base16-bytestring, binary
 , bytestring, Cabal, containers, cryptohash-sha256, deepseq
-, directory, filepath, hackage-security, hashable, HTTP, mtl
-, network, network-uri, pretty, pretty-show, process, QuickCheck
-, random, regex-posix, stdenv, stm, tagged, tar, tasty, tasty-hunit
-, tasty-quickcheck, time, unix, zlib
+, directory, echo, edit-distance, filepath, hackage-security
+, hashable, HTTP, mtl, network, network-uri, pretty, pretty-show
+, process, QuickCheck, random, regex-posix, stdenv, stm, tagged
+, tar, tasty, tasty-hunit, tasty-quickcheck, time, unix, zlib
 }:
 mkDerivation {
   pname = "cabal-install";
   version = "1.25.0.0";
-  src = ./cabal-install;
+  src = ./.;
   isLibrary = false;
   isExecutable = true;
   setupHaskellDepends = [ base Cabal filepath process ];
   executableHaskellDepends = [
     array async base base16-bytestring binary bytestring Cabal
-    containers cryptohash-sha256 deepseq directory filepath
-    hackage-security hashable HTTP mtl network network-uri pretty
-    process random stm tar time unix zlib
+    containers cryptohash-sha256 deepseq directory echo edit-distance
+    filepath hackage-security hashable HTTP mtl network network-uri
+    pretty process random stm tar time unix zlib
   ];
   testHaskellDepends = [
     array async base base16-bytestring binary bytestring Cabal
@@ -25,6 +25,7 @@ mkDerivation {
     pretty-show process QuickCheck random regex-posix stm tagged tar
     tasty tasty-hunit tasty-quickcheck time unix zlib
   ];
+  doCheck = false;
   postInstall = ''
     mkdir $out/etc
     mv bash-completion $out/etc/bash_completion.d

default.nix

@@ -16,7 +16,11 @@ let
 in
 haskellPackages.override {
   overrides = self: super: {
-    Cabal = filterSource (self.callPackage ./Cabal.nix {});
-    cabal-install = filterSource (lib.dontCheck (self.callPackage ./cabal-install.nix {}));
+    Cabal =
+      filterSource (self.callPackage ./Cabal {});
+    cabal-install =
+      filterSource (lib.dontCheck (self.callPackage ./cabal-install {}));
+    hackage-security =
+      lib.dontCheck super.hackage-security;
   };
 }