From a30702135d0f00acad24b94655636e963b24baf3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Vladim=C3=ADr=20=C4=8Cun=C3=A1t?= <vcunat@gmail.com>
Date: Sat, 22 Oct 2016 11:35:56 +0200
Subject: [PATCH] vulkan-loader: convert eval-time checks to build-time

The checks depend on fetched source, so they forced building during
evaluation.
---
 .../libraries/vulkan-loader/default.nix            | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/pkgs/development/libraries/vulkan-loader/default.nix b/pkgs/development/libraries/vulkan-loader/default.nix
index 4dc59bddb6d..4c00bb86142 100644
--- a/pkgs/development/libraries/vulkan-loader/default.nix
+++ b/pkgs/development/libraries/vulkan-loader/default.nix
@@ -14,14 +14,20 @@ let
   getRev = name: builtins.substring 0 40 (builtins.readFile "${src}/${name}_revision");
 in
 
-assert getRev "spirv-tools" == spirv-tools.src.rev;
-assert getRev "spirv-headers" == spirv-tools.headers.rev;
-assert getRev "glslang" == glslang.src.rev;
-
 stdenv.mkDerivation rec {
   name = "vulkan-loader-${version}";
   inherit version src;
 
+  prePatch = ''
+    if [ "$(cat '${src}/spirv-tools_revision')" != '${spirv-tools.src.rev}' ] \
+      || [ "$(cat '${src}/spirv-headers_revision')" != '${spirv-tools.headers.rev}' ] \
+      || [ "$(cat '${src}/glslang_revision')" != '${glslang.src.rev}' ]
+    then
+      echo "Version mismatch, aborting!"
+      false
+    fi
+  '';
+
   buildInputs = [ cmake pkgconfig git python3 python3Packages.lxml
                   glslang spirv-tools x11 libxcb wayland
                 ];