GHCJS support for Dhall (#734)

This adds a GHCJS build for Dhall so that:

* We can build a `try.dhall-lang.org` to try Dhall in the
  browser until the PureScript implementation comes online
* We can document how to build `dhall` using GHCJS
* We can verify that new changes to `dhall` or its dependencies
  don't break GHCJS support
* CI can build and cache GHCJS-related dependencies

nix/cborg.nix

@@ -0,0 +1,21 @@
+{ mkDerivation, aeson, array, base, base16-bytestring
+, base64-bytestring, bytestring, containers, deepseq, fail
+, ghc-prim, half, integer-gmp, primitive, QuickCheck, scientific
+, stdenv, tasty, tasty-hunit, tasty-quickcheck, text, vector
+}:
+mkDerivation {
+  pname = "cborg";
+  version = "0.2.1.0";
+  sha256 = "9198735f7645ae492345505448f790433f5fe407b19e1c6b2ec2a4c76bd97483";
+  libraryHaskellDepends = [
+    array base bytestring containers deepseq ghc-prim half integer-gmp
+    primitive text
+  ];
+  testHaskellDepends = [
+    aeson array base base16-bytestring base64-bytestring bytestring
+    deepseq fail half QuickCheck scientific tasty tasty-hunit
+    tasty-quickcheck text vector
+  ];
+  description = "Concise Binary Object Representation";
+  license = stdenv.lib.licenses.bsd3;
+}

nix/haskeline_0_7_3_1.nix

@@ -0,0 +1,16 @@
+{ mkDerivation, base, bytestring, containers, directory, filepath
+, process, stdenv, stm, transformers, unix
+}:
+mkDerivation {
+  pname = "haskeline";
+  version = "0.7.4.3";
+  sha256 = "046d0930bc2dbc57a7cd9ddb5d1e92c7fdb71c6b91b2bbf673f5406843d6b679";
+  configureFlags = [ "-f-terminfo" ];
+  libraryHaskellDepends = [
+    base bytestring containers directory filepath process stm
+    transformers unix
+  ];
+  homepage = "https://github.com/judah/haskeline";
+  description = "A command-line interface for user input, written in Haskell";
+  license = stdenv.lib.licenses.bsd3;
+}

nix/shared.nix

@@ -57,9 +57,9 @@ let
                     pkgsNew.haskell.lib.dontCheck drv;
 
                 failOnAllWarnings = drv:
-                  # GHC 7.10.3 incorrectly detects non-exhaustive pattern
-                  # matches
-                  if compiler == "ghc7103"
+                  # Older versions of GHC incorrectly detect non-exhaustive
+                  # pattern matches
+                  if compiler == "ghc7103" || compiler == "ghcjs"
                   then drv
                   else pkgsNew.haskell.lib.failOnAllWarnings drv;
 
@@ -69,7 +69,11 @@ let
                     "comonad"
                     "distributive"
                     "doctest"
+                    "half"
+                    "http-types"
+                    "megaparsec"
                     "prettyprinter"
+                    "prettyprinter-ansi-terminal"
                     # https://github.com/well-typed/cborg/issues/172
                     "serialise"
                     "unordered-containers"

release.nix

@@ -5,6 +5,9 @@ let
   shared_8_6_1 =
     import ./nix/shared.nix { compiler = "ghc861"; };
 
+  shared_ghcjs =
+    import ./nix/shared.nix { compiler = "ghcjs"; };
+
   shared =
     import ./nix/shared.nix { };
 
@@ -38,6 +41,9 @@ in
           shared.tarball-dhall-json
           shared.tarball-dhall-text
 
+          # Verify that `dhall` can be built using GHCJS
+          shared_ghcjs.dhall
+
           # This is the only `dhall` build that runs the test suite
           coverage.dhall