gnu: Add elixir-hex.

* gnu/packages/elixir.scm (elixir-hex): New variable.

Change-Id: I957688ae4e078afd79acd439880c38083fdab83a
Signed-off-by: Liliana Marie Prikler <liliana.prikler@gmail.com>

gnu/packages/elixir.scm

@@ -118,3 +118,48 @@ (define-public elixir
 for running low-latency, distributed and fault-tolerant systems, while also
 being successfully used in web development and the embedded software domain.")
     (license license:asl2.0)))
+
+(define-public elixir-hex
+  (package
+    (name "elixir-hex")
+    (version "2.0.5")
+    (source
+     (origin
+       (method git-fetch)
+       (uri (git-reference
+             (url "https://github.com/hexpm/hex.git")
+             (commit (string-append "v" version))))
+       (file-name (git-file-name name version))
+       (sha256
+        (base32
+         "1kvczwvij58kgkhak68004ap81pl26600bczg21mymy2sypkgxmj"))))
+    ;; The mix-build-system assumes that Hex exists.
+    ;; We build Hex using the gnu-build-system.
+    ;; Other Elixir packages use the mix-build-system.
+    (build-system gnu-build-system)
+    (inputs (list elixir))
+    (arguments
+     (list
+      ;; Hex is needed to build packages used to test Hex.
+      ;; To avoid this circularity, we disable tests.
+      #:tests? #f
+      #:phases
+      #~(modify-phases %standard-phases
+          (delete 'bootstrap)
+          (delete 'configure)
+          (replace 'build
+            (lambda* (#:key inputs #:allow-other-keys)
+              (setenv "MIX_ENV" "prod")
+              (invoke "mix" "compile")))
+          (replace 'install
+            (lambda* (#:key inputs outputs #:allow-other-keys)
+              (define X.Y #$(version-major+minor (package-version elixir)))
+              (define out (string-append (assoc-ref outputs "out") "/lib/elixir/" X.Y "/hex"))
+              (mkdir-p out)
+              (copy-recursively "_build/prod/lib/hex" out))))))
+    (synopsis "Package manager for the Erlang VM")
+    (description
+     "This project provides tasks that integrate with Mix, Elixir's build
+tool.")
+    (home-page "https://hexdocs.pm/makeup_elixir/")
+    (license license:bsd-2)))