Add golden coverage test (#964)

* Add golden coverage test

- Other coverage tests check that the coverage tests can be generated,
  but don't check the coverage output itself. This commit adds a test
  to ensure that the coverage output is correct.

* Use niv and haskell.nix for hpc-coveralls

* Get `sources` from `haskell-nix.callPackages`

* Use `builtin: false` for hydra in sources.json

* Fix for cross compilation.

Co-authored-by: Hamish Mackenzie <Hamish.Mackenzie@iohk.io>

nix/sources.json

@@ -12,6 +12,19 @@
         "url": "https://github.com/haskell/cabal/archive/94aaa8e4720081f9c75497e2735b90f6a819b08e.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
+    "cardano-shell": {
+        "branch": "master",
+        "builtin": false,
+        "description": "Node shell, a thin layer for running the node and it's modules.",
+        "homepage": null,
+        "owner": "input-output-hk",
+        "repo": "cardano-shell",
+        "rev": "8e0d6f5548c1c13a9edfeb56e4ea27c0a6d10948",
+        "sha256": "07yjl3agiacmy5irxxmrmm7ffpnvz84zgrylnp3wmcrn417pc5fq",
+        "type": "tarball",
+        "url": "https://github.com/input-output-hk/cardano-shell/archive/8e0d6f5548c1c13a9edfeb56e4ea27c0a6d10948.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
     "ghc-8.6.5-iohk": {
         "branch": "release/8.6.5-iohk",
         "deepClone": true,
@@ -26,6 +39,19 @@
         "url": "https://github.com/input-output-hk/ghc.git",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
+    "hpc-coveralls": {
+        "branch": "master",
+        "builtin": false,
+        "description": "coveralls.io support for haskell code coverage with hpc",
+        "homepage": "http://hackage.haskell.org/package/hpc-coveralls",
+        "owner": "sevanspowell",
+        "repo": "hpc-coveralls",
+        "rev": "14df0f7d229f4cd2e79f8eabb1a740097fdfa430",
+        "sha256": "02dmcmqc845s7sdgdnk3xxn7l6jj8faa7547b4cii9mgv09arspj",
+        "type": "tarball",
+        "url": "https://github.com/sevanspowell/hpc-coveralls/archive/14df0f7d229f4cd2e79f8eabb1a740097fdfa430.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
     "niv": {
         "branch": "master",
         "builtin": false,

test/coverage-golden/default.nix

@@ -0,0 +1,50 @@
+{ stdenv, fetchFromGitHub, recurseIntoAttrs, runCommand, testSrc, compiler-nix-name, buildPackages, sources }:
+
+with stdenv.lib;
+
+let
+  # Using buildPackages.buildPackages here because buildPackages.git
+  # is built with a cross compiler version of gdb (needed by python).
+  # So buildPackages.buildPackages.git is more likely to be in the cache.
+  inherit (buildPackages.buildPackages) jq git;
+
+  hpc-coveralls-exes = (buildPackages.haskell-nix.project' {
+    compiler-nix-name = "ghc865"; # TODO use `inherit compiler-nix-name;` once it is working with 8.8 and 8.10
+    src = sources.hpc-coveralls;
+  }).hsPkgs.hpc-coveralls.components.exes;
+  
+  exampleProjectSrc = sources.cardano-shell;
+
+  exampleProject = import "${exampleProjectSrc}" { config = { haskellNix = { coverage = true; }; }; };
+  exampleCoverageReport = exampleProject.cardanoShellHaskellPackages.projectCoverageReport;
+
+in recurseIntoAttrs ({
+  run = stdenv.mkDerivation {
+    name = "coverage-golden-test";
+
+    nativeBuildInputs = [ git jq hpc-coveralls-exes.hpc-coveralls hpc-coveralls-exes.run-cabal-test ];
+    buildCommand = ''
+      ########################################################################
+      # Test that the coverage reports haven't materially changed
+
+      TRAVIS=1 TRAVIS_JOB_ID=1 hpc-coveralls all \
+        --package-dir ${exampleProjectSrc}/cardano-shell/ \
+        --package-dir ${exampleProjectSrc}/cardano-launcher \
+        --hpc-dir ${exampleCoverageReport}/share/hpc/vanilla \
+        --coverage-mode StrictlyFullLines \
+        --dont-send
+
+      # Format JSON for better diffing error messages and remove
+      # references to Nix path, our golden coverage file contains no
+      # Nix paths
+      cat ./travis-ci-1.json | jq -S | sed "s;${exampleProjectSrc}/;;g" > ./actual.json
+
+      # Fail if doesn't match golden, i.e. our coverage has changed
+      diff ${./golden.json} ./actual.json
+
+      touch $out
+    '';
+
+    meta.platforms = platforms.all;
+  };
+})

test/default.nix

@@ -193,6 +193,7 @@ let
   } // lib.optionalAttrs (!stdenv.hostPlatform.isGhcjs) {
     # These do not work on ghcjs because it needs zlib.
     coverage = callTest ./coverage { inherit compiler-nix-name; };
+    coverage-golden = callTest ./coverage-golden { inherit compiler-nix-name;};
     coverage-no-libs = callTest ./coverage-no-libs { inherit compiler-nix-name; };
     snapshots = callTest ./snapshots {};
   } // lib.optionalAttrs (!stdenv.hostPlatform.isGhcjs && compiler-nix-name != "ghc8101" && compiler-nix-name != "ghc8102" && compiler-nix-name != "ghc810220201118" ) {