Add a Nix CI job

Author: pepeiborra

.circleci/config.yml

@@ -156,6 +156,32 @@ jobs:
           key: cabal-{{ .Environment.HIE_CACHE }}-{{ arch }}-{{ .Environment.CIRCLE_JOB }}
           paths:
             - ~/.cabal
+  nix:
+    working_directory: ~/build
+    environment:
+        - NIXPKGS_ALLOW_BROKEN: 1
+    docker:
+        - image: nixorg/nix:circleci
+    steps:
+      - checkout
+      - run:
+          name: Sync submodules
+          command: git submodule sync --recursive
+      - run:
+          name: Update submodules
+          command: git submodule update --recursive --init
+      - restore-cache:
+          keys:
+            - cabal-{{ .Environment.HIE_CACHE }}-{{ arch }}-{{ .Environment.CIRCLE_JOB }}
+      - run:
+          name: Build
+          command: nix-shell -j4 --run "cabal new-update && cabal new-build -j1 --enable-tests"
+          no_output_timeout: 30m
+      - save_cache:
+          key: cabal-{{ .Environment.HIE_CACHE }}-{{ arch }}-{{ .Environment.CIRCLE_JOB }}
+          paths:
+            - ~/.cabal
+
 
 
 workflows:
@@ -170,3 +196,4 @@ workflows:
       - ghc-8.10.1
       # - ghc-nightly
       - cabal
+      - nix