From 08b766921dce9ff67c644ad65135ce57aaaf796b Mon Sep 17 00:00:00 2001
From: Will Fancher <elvishjerricco@gmail.com>
Date: Thu, 2 Aug 2018 09:48:06 -0400
Subject: [PATCH] callCabal2nix: Passthru deriver

---
 pkgs/development/haskell-modules/make-package-set.nix | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/pkgs/development/haskell-modules/make-package-set.nix b/pkgs/development/haskell-modules/make-package-set.nix
index 87ac65307aa..095a3290343 100644
--- a/pkgs/development/haskell-modules/make-package-set.nix
+++ b/pkgs/development/haskell-modules/make-package-set.nix
@@ -159,6 +159,13 @@ let
         # Generated from ${src}
         ${orig.preConfigure or ""}
       '';
+      passthru = orig.passthru or {} // {
+        # When using callCabal2nix or callHackage, it is often useful
+        # to debug a failure by inspecting the Nix expression
+        # generated by cabal2nix. This can be accessed via this
+        # cabal2nixDeriver field.
+        cabal2nixDeriver = src;
+      };
     });
 
 in package-set { inherit pkgs stdenv callPackage; } self // {