Update to current nixpkgs-unstable

This required the introduction of an overlay file since ofBorg still
requires openssl 1.0.2. Updating to newer version of openssl also
requires updating the amqp library which requires some more involved
changes.

The php code is only updated to php 7.2 and not 7.3 (the default in
nixpkgs) since there seem to been a few syntax changes that aren't yet
compatible with composer2nix.

In previous versions of the rust infrastructure within nixpkgs we would
have been able to override all crates during the invocation of the
target crate. That `override` feature was removed as it caused a huge
eval overhead for larger projects. We did end up with (n^2)
instantiations of dependencies since they were being overriden on every
invocation of every dependency on every level further down the chain.
The current understanding is that the build tooling that each project is
using (e.g.  crate2nix, crate2nix, …) that is driving the actual build
could easily reintroduce that feature without the overhead.

pin to php72

default.nix

@@ -1,4 +1,4 @@
-{ pkgs ? import ./nix {} }:
+{ pkgs ? import ./nix { overlays = [ (import ./nix/overlay.nix) ]; } }:
 
 let
   ofborgOverrides = {

nix/nixpkgs.json

@@ -1,7 +1,7 @@
 {
   "url": "https://github.com/nixos/nixpkgs-channels.git",
-  "rev": "201d739b0ffbebceb444864d1856babcd1a666a8",
+  "rev": "e2b4abe3c8f2e09adfc6a52007841d1b96c89371",
-  "date": "2018-12-30T01:29:37+00:00",
+  "date": "2020-02-19T01:57:21+01:00",
-  "sha256": "0mfkzmylglpw84w85zs3djpspcx45bg3s62hk4j44dxl2p0fvggj",
+  "sha256": "1l3jfr74s7wmx3fk5y76ayazbfclvnr532kg1hypbzydp3n372rz",
   "fetchSubmodules": false
 }

nix/overlay.nix

@@ -0,0 +1,12 @@
+(self: super: {
+  defaultCrateOverrides = super.defaultCrateOverrides // {
+    openssl-sys = attrs: {
+      buildInputs = [ self.openssl_1_0_2 ];
+      nativeBuildInputs = [ self.pkgconfig ];
+    };
+    openssl = attrs: {
+      DEP_OPENSSL_VERSION = "102";
+    };
+  };
+})
+

php/default.nix

@@ -4,10 +4,11 @@
 
 let
   composerEnv = import ./composer-env.nix {
-    inherit (pkgs) stdenv writeTextFile fetchurl php unzip;
+    inherit (pkgs) stdenv writeTextFile fetchurl unzip;
+    php = pkgs.php72;
   };
 in
 import ./php-packages.nix {
   inherit composerEnv noDev;
   inherit (pkgs) fetchurl fetchgit fetchhg fetchsvn;
-}
+}

release.nix

@@ -15,7 +15,12 @@ let
     (collector: system:
       collector // {
         "${system}" = import ./. {
-          pkgs = import nixpkgs { inherit system; };
+          pkgs = import nixpkgs {
+            inherit system;
+            overlays = [
+              (import ./nix/overlay.nix)
+            ];
+          };
         };
       }
     )