elm-format: init at 0.3.1

Closes #15817.

abbradar: remove unneeded callPackage argument and clean up spaces.

pkgs/development/compilers/elm/default.nix

@@ -63,6 +63,16 @@ let
                 '';
             });
 
+            /*
+            This is not a core Elm package, and it's hosted on GitHub.
+            To update, run:
+
+                cabal2nix --jailbreak --revision refs/tags/foo http://github.com/avh4/elm-format > packages/elm-format.nix
+
+            where foo is a tag for a new version, for example "0.3.1-alpha".
+            */
+            elm-format = self.callPackage ./packages/elm-format.nix { };
+
           };
       in elmPkgs // {
         inherit elmPkgs;

pkgs/development/compilers/elm/packages/elm-format.nix

@@ -0,0 +1,36 @@
+{ mkDerivation, aeson, ansi-terminal, ansi-wl-pprint, base, binary
+, bytestring, containers, directory, edit-distance, fetchgit
+, filemanip, filepath, HUnit, indents, mtl, optparse-applicative
+, parsec, pretty, process, QuickCheck, quickcheck-io
+, regex-applicative, split, stdenv, test-framework
+, test-framework-hunit, test-framework-quickcheck2, text
+, union-find, wl-pprint
+}:
+mkDerivation {
+  pname = "elm-format";
+  version = "0.3.1";
+  src = fetchgit {
+    url = "http://github.com/avh4/elm-format";
+    sha256 = "04kl50kzvjf4i140dlhs6f9fd2wmk6cnvyfamx2xh8vbwbnwrkj4";
+    rev = "0637f3772de2297d12ea35f5b66961e1d827552c";
+  };
+  isLibrary = false;
+  isExecutable = true;
+  executableHaskellDepends = [
+    aeson ansi-terminal ansi-wl-pprint base binary bytestring
+    containers directory edit-distance filemanip filepath indents mtl
+    optparse-applicative parsec pretty process regex-applicative split
+    text
+  ];
+  testHaskellDepends = [
+    aeson ansi-terminal base binary bytestring containers directory
+    edit-distance filemanip filepath HUnit indents mtl parsec pretty
+    process QuickCheck quickcheck-io regex-applicative split
+    test-framework test-framework-hunit test-framework-quickcheck2 text
+    union-find wl-pprint
+  ];
+  jailbreak = true;
+  homepage = "http://elm-lang.org";
+  description = "A source code formatter for Elm";
+  license = stdenv.lib.licenses.bsd3;
+}