Use a host-only Nixpkgs for test environment

Discriminate test-packages and host-packages when building tests.
This avoids the test tooling being tainted with the hostPlatform
and targetPlatform of the test. For example, QEMU must be built
independently and isolated from the guest platform, for the sake
of test control and minimizing rebuilds.

default.nix

@@ -16,12 +16,7 @@ let
   toolchainOverlay = import ./toolchain-overlay;
   # Overlay of toolchain patches
 
-  nixpkgs' = builtins.fetchGit {
-    # A branch of Nixpkgs with a custom "crossSystem" mechanism
-    url = "https://github.com/ehmry/nixpkgs.git";
-    ref = "hybrid-19.09";
-    rev = "9a704b7def9bc9ea04d12d6a0d55ebebe0af982a";
-  };
+  nixpkgs' = import ./nixpkgs.nix;
 
 in { nixpkgs ? nixpkgs', dhall-haskell ? ./dhall-haskell.nix }:
 

nixpkgs.nix

@@ -0,0 +1,6 @@
+# A branch of Nixpkgs with a custom "crossSystem" mechanism
+builtins.fetchGit {
+  url = "https://github.com/ehmry/nixpkgs.git";
+  ref = "hybrid-19.09";
+  rev = "9a704b7def9bc9ea04d12d6a0d55ebebe0af982a";
+}

tests/default.nix

@@ -10,21 +10,24 @@ let
     signal = call ./signal.nix { };
     solo5 = call ./solo5.nix { };
   };
-in { pkgs ? (import ./.. { }) }:
+  nixpkgs' = import ./../nixpkgs.nix;
+in { nixpkgs ? nixpkgs' }:
 
 let
+  hostPkgs = import nixpkgs { };
+  testPkgs = import ./.. { inherit nixpkgs; };
 
-  lib = pkgs.buildPackages.pkgs.lib // {
+  lib = hostPkgs.lib // {
 
     renderDhallInit = path: args:
-      pkgs.buildPackages.runCommand "init.xml" {
-        buildInputs = with pkgs.buildPackages; [ linux-dhall ];
+      hostPkgs.runCommand "init.xml" {
+        buildInputs = [ testPkgs.buildPackages.linux-dhall ];
         initConfig = path;
         initArgs = args;
-        DHALL_PRELUDE = "${pkgs.dhallPackages.prelude}/package.dhall";
-        DHALL_GENODE = "${pkgs.dhallPackages.genode}/package.dhall";
+        DHALL_PRELUDE = "${testPkgs.dhallPackages.prelude}/package.dhall";
+        DHALL_GENODE = "${testPkgs.dhallPackages.genode}/package.dhall";
       } ''
-        set -v
+        export XDG_CACHE_HOME=$NIX_BUILD_TOP
         echo 'let Prelude = env:DHALL_GENODE in Prelude.Init.render (Prelude.Init.defaults ⫽ { children =  toMap (env:initConfig env:initArgs) })' \
           | dhall text \
           > $out
@@ -33,5 +36,6 @@ let
   };
 
 in {
-  linux = tests (import ./driver-linux.nix { inherit pkgs lib; }).callTest;
+  linux = tests
+    (import ./driver-linux.nix { inherit testPkgs hostPkgs lib; }).callTest;
 }

tests/driver-linux.nix

@@ -2,10 +2,10 @@
 #
 # SPDX-License-Identifier: LicenseRef-Hippocratic-1.1
 
-{ pkgs, lib }:
+{ testPkgs, hostPkgs, lib }:
 
 let
-  testDriver = with pkgs.buildPackages;
+  testDriver = with hostPkgs;
     stdenv.mkDerivation {
       name = "genode-test-driver";
 
@@ -23,7 +23,7 @@ let
     };
 
   runTests = driver:
-    pkgs.stdenv.mkDerivation {
+    hostPkgs.stdenv.mkDerivation {
       name = "test-run-${driver.testName}";
 
       buildCommand = ''
@@ -39,7 +39,7 @@ let
   makeTest = { testScript, testConfig, name ? "unamed", ... }@t:
     let
 
-      baseSetup = with pkgs; ''
+      baseSetup = with testPkgs; ''
         file link -s core ${depot.base-linux}/bin/core
         file link -s timer ${depot.base-linux}/bin/timer
         file link -s ld.lib.so ${depot.base-linux}/lib/ld.lib.so
@@ -48,22 +48,23 @@ let
         file link -s test.config $env(testConfig)
       '';
 
-      driver = pkgs.buildPackages.runCommand "genode-test-driver-${name}" {
-        buildInputs = with pkgs.buildPackages; [ makeWrapper expect ];
-        inherit baseSetup testConfig testScript;
-        preferLocalBuild = true;
-        testName = name;
-      } ''
-        mkdir -p $out/bin
-        echo "$testConfig" > $out/test.config
-        echo "$testScript" > $out/test-script
-        echo "$baseSetup" > $out/base-setup
-        ln -s ${testDriver}/bin/genode-test-driver $out/bin/
-        wrapProgram $out/bin/genode-test-driver \
-          --run "export testConfig=\"$testConfig\"" \
-          --run "export testScript=\"\$(cat $out/test-script)\"" \
-          --run "export baseSetup=\"\$(cat $out/base-setup)\"" \
-      '';
+      driver = with hostPkgs;
+        runCommand "genode-test-driver-${name}" {
+          buildInputs = [ makeWrapper expect ];
+          inherit baseSetup testConfig testScript;
+          preferLocalBuild = true;
+          testName = name;
+        } ''
+          mkdir -p $out/bin
+          echo "$testConfig" > $out/test.config
+          echo "$testScript" > $out/test-script
+          echo "$baseSetup" > $out/base-setup
+          ln -s ${testDriver}/bin/genode-test-driver $out/bin/
+          wrapProgram $out/bin/genode-test-driver \
+            --run "export testConfig=\"$testConfig\"" \
+            --run "export testScript=\"\$(cat $out/test-script)\"" \
+            --run "export baseSetup=\"\$(cat $out/base-setup)\"" \
+        '';
 
       passMeta = drv:
         drv
@@ -74,5 +75,9 @@ let
     in test // { inherit driver test; };
 
 in {
-  callTest = path: args: makeTest (import path ({ inherit pkgs lib; } // args));
+  callTest = path: args:
+    makeTest (import path ({
+      pkgs = testPkgs;
+      inherit lib;
+    } // args));
 }