From 94815133604a0ff3b8831a6322c3b0138c2f0d96 Mon Sep 17 00:00:00 2001
From: Bas van Dijk <v.dijk.bas@gmail.com>
Date: Sat, 11 Aug 2018 10:44:27 +0200
Subject: [PATCH] cabal2nix: fix build by overriding hpack to 0.29.6

Fixes: https://github.com/NixOS/cabal2nix/issues/369
---
 .../haskell-modules/configuration-common.nix  | 20 ++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/pkgs/development/haskell-modules/configuration-common.nix b/pkgs/development/haskell-modules/configuration-common.nix
index f29b83c8ff92..9b9b3ec63c29 100644
--- a/pkgs/development/haskell-modules/configuration-common.nix
+++ b/pkgs/development/haskell-modules/configuration-common.nix
@@ -1080,13 +1080,19 @@ self: super: {
   haddock-library = doJailbreak (dontCheck super.haddock-library);
   haddock-library_1_6_0 = doJailbreak (dontCheck super.haddock-library_1_6_0);
 
-  # The test suite does not know how to find the 'cabal2nix' binary.
-  cabal2nix = overrideCabal super.cabal2nix (drv: {
-    preCheck = ''
-      export PATH="$PWD/dist/build/cabal2nix:$PATH"
-      export HOME="$TMPDIR/home"
-    '';
-  });
+  cabal2nix =
+    let
+      # The test suite does not know how to find the 'cabal2nix' binary.
+      drv1 = overrideCabal super.cabal2nix (drv: {
+               preCheck = ''
+                 export PATH="$PWD/dist/build/cabal2nix:$PATH"
+                 export HOME="$TMPDIR/home"
+               '';
+             });
+       # cabal2nix requires hpack >= 0.29.6 but the LTS has hpack-0.28.2.
+       # Lets remove this once the LTS has upraded to 0.29.6.
+       drv2 = drv1.override { hpack = self.hpack_0_29_6; };
+    in drv2;
 
   # Break out of "aeson <1.3, temporary <1.3".
   stack = doJailbreak super.stack;