artiq: pass wrapped python env to subprocesses

Fixes https://github.com/m-labs/artiq-comtools/issues/7.
Basically, python subprocesses can't see all installed python packages
in a python environment because it uses the wrong Python exe (i.e. it
doesn't use the wrapped exe). This patches the PATH in the binary
wrappers (e.g. */bin/artiq_session) to include the correct python path.

artiq-fast/pkgs/artiq.nix

@@ -21,6 +21,10 @@ python3Packages.buildPythonPackage rec {
     wrapQtApp "$out/bin/artiq_session"
   '';
 
+  # Modifies PATH to pass the wrapped python environment (i.e. python3.withPackages(...) to subprocesses.
+  # Allows subprocesses using python to find all packages you have installed
+  makeWrapperArgs = [ ''--run 'if [ ! -z "$NIX_PYTHONPREFIX" ]; then export PATH=$NIX_PYTHONPREFIX/bin:$PATH;fi' '' ];
+
   checkInputs = [ binutils-or1k outputcheck ];
   checkPhase =
   ''

artiq-full/extras.nix

@@ -195,6 +195,9 @@ in
         sha256 = "165j12k9nnrkf2pv0idcv6xhnp1hnsllna4rps2dssnqgjfaw1ss";
       };
       propagatedBuildInputs = [ sipyco pkgs.python3Packages.numpy pkgs.python3Packages.aiohttp ];
+      # Modifies PATH to pass the wrapped python environment (i.e. python3.withPackages(...) to subprocesses.
+      # Allows subprocesses using python to find all packages you have installed
+      makeWrapperArgs = [ ''--run 'if [ ! -z "$NIX_PYTHONPREFIX" ]; then export PATH=$NIX_PYTHONPREFIX/bin:$PATH;fi' '' ];
     };
     conda-artiq-comtools = condaBuild {
       name = "conda-artiq-comtools";