From 2645e1a1eb41742905394db9d7679a1bb3343eeb Mon Sep 17 00:00:00 2001
From: Georges Dubus <georges.dubus@gmail.com>
Date: Wed, 26 Feb 2020 15:26:14 +0100
Subject: [PATCH] cabal2nix: split into a lightweight version and a wrapper

Current, the `cabal2nix` derivation contains both the executable, and a wrapper
that adds `nix` and `nix-prefetch-scripts`, which are required for some
features.

However, when calling `callCabal2nix` to create a derivation from a cabal file
at evaluation time,
these features are not actually used, but the huge closure of
`nix-prefetch-scripts` (which includes multiple vcs, as well as python and perl)
still needs to be fetched.

This commit splits cabal2nix into a lightweight version that is a standalone
static binary (`cabal2nix-unwrapped`), and a wrapper that includes the proper
dependencies in the path for full usage of the command line
utility (`cabal2nix`).

This commit also switches to the default ghc, to reduce the likelyhood of
building a different ghc when calling `callCabal2nix`.
---
 .../haskell-modules/make-package-set.nix      |  2 +-
 pkgs/top-level/all-packages.nix               | 24 +++++++++----------
 2 files changed, 12 insertions(+), 14 deletions(-)

diff --git a/pkgs/development/haskell-modules/make-package-set.nix b/pkgs/development/haskell-modules/make-package-set.nix
index 17fb1ab8ae8..1418cfef057 100644
--- a/pkgs/development/haskell-modules/make-package-set.nix
+++ b/pkgs/development/haskell-modules/make-package-set.nix
@@ -124,7 +124,7 @@ let
       sha256Arg = if sha256 == null then "--sha256=" else ''--sha256="${sha256}"'';
     in buildPackages.stdenv.mkDerivation {
       name = "cabal2nix-${name}";
-      nativeBuildInputs = [ buildPackages.cabal2nix ];
+      nativeBuildInputs = [ buildPackages.cabal2nix-unwrapped ];
       preferLocalBuild = true;
       allowSubstitutes = false;
       phases = ["installPhase"];
diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index bcf0a5871a4..16ace1102cc 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -1342,19 +1342,17 @@ in
 
   cue2pops = callPackage ../tools/cd-dvd/cue2pops { };
 
-  cabal2nix = haskell.lib.overrideCabal (haskell.lib.generateOptparseApplicativeCompletion "cabal2nix" haskell.packages.ghc881.cabal2nix) (drv: {
-    isLibrary = false;
-    enableSharedExecutables = false;
-    executableToolDepends = (drv.executableToolDepends or []) ++ [ makeWrapper ];
-    postInstall = ''
-      exe=$out/libexec/${drv.pname}-${drv.version}/${drv.pname}
-      install -D $out/bin/${drv.pname} $exe
-      rm -rf $out/{bin,lib,share}
-      makeWrapper $exe $out/bin/${drv.pname} \
-        --prefix PATH ":" "${nix}/bin" \
-        --prefix PATH ":" "${nix-prefetch-scripts}/bin"
-    '' + (drv.postInstall or "");
-  });
+  cabal2nix-unwrapped = haskell.lib.justStaticExecutables (haskell.lib.generateOptparseApplicativeCompletion "cabal2nix" haskellPackages.cabal2nix);
+
+  cabal2nix = symlinkJoin {
+    inherit (cabal2nix-unwrapped) name meta;
+    nativeBuildInputs = [ makeWrapper ];
+    paths = [ cabal2nix-unwrapped ];
+    postBuild = ''
+      wrapProgram $out/bin/cabal2nix \
+        --prefix PATH ":" "${lib.makeBinPath [ nix nix-prefetch-scripts ]}"
+    '';
+  };
 
   stack2nix = with haskell.lib; overrideCabal (justStaticExecutables haskellPackages.stack2nix) (drv: {
     executableToolDepends = [ makeWrapper ];