basic flake.nix support with lib.packs

impure and sandbox options should be passed as:

$ nix build .#pkgs.zlib -L --impure --option sandbox false

flake.nix

@@ -0,0 +1,120 @@
+{
+  description = "Flake for NixPACK";
+
+  inputs.spack = { url="github:spack/spack"; flake=false; };
+  #inputs.spack = { url="github:flatironinstitute/spack/fi-nixpack"; flake=false; };
+  inputs.nixpkgs.url = "github:dguibert/nixpkgs/pu-nixpack";
+
+  outputs = inputs: let
+    nixpkgsFor = system: import inputs.nixpkgs {
+      inherit system;
+      config = {
+        replaceStdenv = import ./nixpkgs/stdenv.nix;
+        allowUnfree = true;
+        cudaSupport = true;
+      };
+      overlays = [(import ./nixpkgs/overlay.nix)];
+    };
+
+    nixosPacks = system: let
+      pkgs = nixpkgsFor system;
+      gccWithFortran = pkgs.wrapCC (pkgs.gcc.cc.override {
+        langFortran = true;
+      });
+    in inputs.self.lib.packs {
+      inherit system;
+      os = "nixos21";
+      global.verbose = "true";
+      spackConfig.config.source_cache="/tmp/spack_cache";
+      spackPython = "${pkgs.python3}/bin/python3";
+      spackEnv   = {
+        # pure environment PATH
+        PATH=/*"/run/current-system/sw/bin:"
+            +*/inputs.nixpkgs.lib.concatStringsSep ":"
+            (builtins.map (x: "${x}/bin")
+            [
+              pkgs.bash
+              pkgs.coreutils
+              pkgs.gnumake
+              pkgs.gnutar
+              pkgs.gzip
+              pkgs.bzip2
+              pkgs.xz
+              pkgs.gawk
+              pkgs.gnused
+              pkgs.gnugrep
+              pkgs.glib
+              pkgs.binutils.bintools # glib: locale
+              pkgs.patch
+              pkgs.texinfo
+              pkgs.diffutils
+              pkgs.pkgconfig
+              pkgs.gitMinimal
+              pkgs.findutils
+            ]);
+        #PATH="/run/current-system/sw/bin:${pkgs.gnumake}/bin:${pkgs.binutils.bintools}/bin";
+        LOCALE_ARCHIVE="/run/current-system/sw/lib/locale/locale-archive";
+        LIBRARY_PATH=/*"/run/current-system/sw/bin:"
+            +*/inputs.nixpkgs.lib.concatStringsSep ":"
+            (builtins.map (x: "${x}/lib")
+            [
+              (inputs.nixpkgs.lib.getLib pkgs.binutils.bintools) # ucx (configure fails) libbfd not found
+	    ]);
+      };
+
+      package = {
+        compiler = { name="gcc"; extern=gccWithFortran; version=gccWithFortran.version; };
+        perl = { extern=pkgs.perl; version=pkgs.perl.version; };
+        openssh = { extern=pkgs.openssh; version=pkgs.openssh.version; };
+        openssl = { extern=pkgs.symlinkJoin { name="openssl"; paths = [ pkgs.openssl.all ]; }; version=pkgs.openssl.version; };
+        openmpi = {
+          version = "4.1";
+          variants = {
+            fabrics = {
+              none = false;
+              ucx = true;
+            };
+            schedulers = {
+              none = false;
+              slurm = false;
+            };
+            pmi = false;
+            pmix = false;
+            static = false;
+            thread_multiple = true;
+            legacylaunchers = true;
+          };
+        };
+      };
+      repoPatch = {
+        dyninst = spec: old: {
+          patches = [ ./patch/dyninst-nixos.patch ];
+        };
+        openmpi = spec: old: {
+          build = {
+            setup = ''
+              configure_args = pkg.configure_args()
+              if spec.satisfies("~pmix"):
+                if '--without-mpix' in configure_args: configure_args.remove('--without-pmix')
+              pkg.configure_args = lambda: configure_args
+            '';
+          };
+        };
+      };
+    };
+  in {
+    lib = (import packs/lib.nix) // {
+      packs = {
+        ...
+      }@args: import ./packs ({
+        inherit (inputs) spack nixpkgs;
+      } // args);
+    };
+
+
+    packages.x86_64-linux = nixosPacks "x86_64-linux";
+
+    defaultPackage.x86_64-linux = inputs.self.packages.x86_64-linux.hello;
+
+  };
+}

nixpkgs/overlay.nix

@@ -2,23 +2,37 @@ self: pkgs:
 with pkgs;
 
 {
+  coreutils = coreutils.overrideAttrs (old: {
+    doCheck = false; # failure test-getaddrinfo
+  });
+  gnutls = gnutls.overrideAttrs (old: {
+    doCheck = false; # failure test-getaddrinfo
+  });
+  libgpg-error = libgpg-error.overrideAttrs (old: {
+    doCheck = false; # failure FAIL: t-argparse 1.42
+  });
+  p11-kit = p11-kit.overrideAttrs (old: {
+    doCheck = false; # failure ERROR: test-path - missing test plan
+  });
+
   nss_sss = callPackage sssd/nss-client.nix { };
 
   libuv = libuv.overrideAttrs (old: {
     doCheck = false; # failure
   });
 
-  coreutils = coreutils.overrideAttrs (old: {
-    doCheck = false; # df/total-verify broken on ceph
-  });
-
   nix = (nix.override {
     withAWS = false;
   }).overrideAttrs (old: {
     patches = [../patch/nix-ignore-fsea.patch];
     doInstallCheck = false;
   });
 
+  git = git.overrideAttrs (old: {
+    doCheck = false; # failure
+    doInstallCheck = false; # failure
+  });
+
   gtk3 = gtk3.override {
     trackerSupport = false;
   };
@@ -33,6 +47,10 @@ with pkgs;
     '';
   });
 
+  openssh = openssh.overrideAttrs (old: {
+    doCheck = false; # failure
+  });
+
   openssl_1_0_2 = openssl_1_0_2.overrideAttrs (old: {
     postPatch = old.postPatch + ''
       sed -i 's:define\s\+X509_CERT_FILE\s\+.*$:define X509_CERT_FILE "/etc/pki/tls/certs/ca-bundle.crt":' crypto/cryptlib.h

patch/dyninst-nixos.patch

@@ -0,0 +1,20 @@
+diff --git a/scripts/dynsysname b/scripts/dynsysname
+index 6906fb224..ce385e046 100755
+--- a/scripts/dynsysname
++++ b/scripts/dynsysname
+@@ -1,4 +1,4 @@
+-#!/bin/bash
++#!/usr/bin/env bash
+
+ P=$1
+
+diff --git a/scripts/sysname b/scripts/sysname
+index 16f540483..dccd3e677 100755
+--- a/scripts/sysname
++++ b/scripts/sysname
+@@ -1,4 +1,4 @@
+-#!/bin/bash
++#!/usr/bin/env bash
+ # $Id: sysname,v 1.6 2005/08/09 16:13:16 gquinn Exp $
+ # Attempt to guess a canonical system name.
+ #   Copyright (C) 1992, 1993, 1994, 1995 Free Software Foundation, Inc.