crystal2nix: Put it into pkgs

pkgs/development/compilers/crystal/crystal2nix.cr

@@ -26,7 +26,7 @@ File.open "shards.nix", "w+" do |file|
 
     sha256 = ""
     args = ["--url", url, "--rev", rev]
-    Process.run("nix-prefetch-git", args: args) do |x|
+    Process.run("@nixPrefetchGit@", args: args) do |x|
       x.error.each_line { |e| puts e }
       sha256 = PrefetchJSON.from_json(x.output).sha256
     end

pkgs/development/compilers/crystal/crystal2nix.nix

@@ -0,0 +1,16 @@
+{ lib, crystal, nix-prefetch-git }:
+crystal.buildCrystalPackage {
+  pname = "crystal2nix";
+  version = "unstable-2018-07-31";
+
+  nixPrefetchGit = "${lib.getBin nix-prefetch-git}/bin/nix-prefetch-git";
+  unpackPhase = "substituteAll ${./crystal2nix.cr} crystal2nix.cr";
+
+  crystalBinaries.crystal2nix.src = "crystal2nix.cr";
+
+  meta = with lib; {
+    description = "Utility to convert Crystal's shard.lock files to a Nix file";
+    license = licenses.mit;
+    maintainers = [ maintainers.manveru ];
+  };
+}

pkgs/development/compilers/crystal/default.nix

@@ -212,4 +212,6 @@ in rec {
   };
 
   crystal = crystal_0_30;
+
+  crystal2nix = callPackage ./crystal2nix.nix {};
 }

pkgs/top-level/all-packages.nix

@@ -7453,7 +7453,8 @@ in
     crystal_0_27
     crystal_0_29
     crystal_0_30
-    crystal;
+    crystal
+    crystal2nix;
 
   icr = callPackage ../development/tools/icr {};