From 233cec301c8cdf8b34e702a67ee26230c1222e01 Mon Sep 17 00:00:00 2001
From: Robert Hensing <robert@roberthensing.nl>
Date: Thu, 14 May 2020 15:26:01 +0200
Subject: [PATCH] haskell/generic-builder.nix: Fix C lib multiple inclusions

Allow the darwin links code to overwrite libs that were already
copied, because C dependencies can occur multiple times.

Solves errors like

    ln: failed to create symbolic link '/nix/store/higpc9xavwcjjzdipz7m9ly03bh7iy2z-hercules-ci-agent-source-0.7.0/lib/links/libboost_context.dylib': File exists

(cherry picked from commit a9373cdb0aeca1bef291d74be1cecdca8e0c3c27)
---
 pkgs/development/haskell-modules/generic-builder.nix | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/pkgs/development/haskell-modules/generic-builder.nix b/pkgs/development/haskell-modules/generic-builder.nix
index 513987dae7b3..bcaf522404e4 100644
--- a/pkgs/development/haskell-modules/generic-builder.nix
+++ b/pkgs/development/haskell-modules/generic-builder.nix
@@ -385,7 +385,8 @@ stdenv.mkDerivation ({
 
     for d in $(grep '^dynamic-library-dirs:' "$packageConfDir"/* | cut -d' ' -f2- | tr ' ' '\n' | sort -u); do
       for lib in "$d/"*.dylib; do
-        ln -s "$lib" "$dynamicLinksDir"
+        # Allow overwriting because C libs can be pulled in multiple times.
+        ln -sf "$lib" "$dynamicLinksDir"
       done
     done
     # Edit the local package DB to reference the links directory.