nixos/test-driver: Typecheck TestScript

nixos/lib/testing-python.nix

@@ -85,7 +85,7 @@ rec {
 
       nodeHostNames = let
         nodesList = map (c: c.config.system.name) (lib.attrValues nodes);
-      in nodesList ++ lib.optional (lib.length nodesList == 1) "machine";
+      in nodesList ++ lib.optional (lib.length nodesList == 1 && !lib.elem "machine" nodesList) "machine";
 
       # TODO: This is an implementation error and needs fixing
       # the testing famework cannot legitimately restrict hostnames further
@@ -100,6 +100,9 @@ rec {
         then testScript { inherit nodes; }
         else testScript;
 
+      uniqueVlans = lib.unique (builtins.concatLists vlans);
+      vlanNames = map (i: "vlan${toString i}: VLan;") uniqueVlans;
+      machineNames = map (name: "${name}: Machine;") nodeHostNames;
     in
     if lib.length invalidNodeNames > 0 then
       throw ''
@@ -113,7 +116,7 @@ rec {
     else lib.warnIf skipLint "Linting is disabled" (runCommand testDriverName
       {
         inherit testName;
-        nativeBuildInputs = [ makeWrapper ];
+        nativeBuildInputs = [ makeWrapper mypy ];
         testScript = testScript';
         preferLocalBuild = true;
         passthru = passthru // {
@@ -125,7 +128,23 @@ rec {
         mkdir -p $out/bin
 
         vmStartScripts=($(for i in ${toString vms}; do echo $i/bin/run-*-vm; done))
-        echo -n "$testScript" > $out/test-script
+
+        # prepend type hints so the test script can be type checked with mypy
+        cat "${./test-script-prepend.py}" >> testScriptWithTypes
+        echo "${builtins.toString machineNames}" >> testScriptWithTypes
+        echo "${builtins.toString vlanNames}" >> testScriptWithTypes
+        echo -n "$testScript" >> testScriptWithTypes
+
+        # set pythonpath so mypy knows where to find the imports. this requires the py.typed file.
+        export PYTHONPATH='${./test-driver}'
+        mypy  --no-implicit-optional \
+              --pretty \
+              --no-color-output \
+              testScriptWithTypes
+        unset PYTHONPATH
+
+        echo -n "$testScript" >> $out/test-script
+
         ln -s ${testDriver}/bin/nixos-test-driver $out/bin/nixos-test-driver
 
         ${testDriver}/bin/generate-driver-symbols