xonsh: Add wrapper

It is currently not obvious how to install/use xonsh with dependencies and python packages.

This PR implements a wrapper that allows you to construct a custom xonsh environment by using:
``` nix
xonsh.override { extraPackages = ps: [ ps.requests ]; }
```

nixos/modules/programs/xonsh.nix

@@ -28,7 +28,7 @@ in
         type = types.package;
         default = pkgs.xonsh;
         defaultText = literalExpression "pkgs.xonsh";
-        example = literalExpression "pkgs.xonsh.override { configFile = \"/path/to/xonshrc\"; }";
+        example = literalExpression "pkgs.xonsh.override { extraPackages = ps: [ ps.requests ]; }";
         description = lib.mdDoc ''
           xonsh package to use.
         '';
@@ -83,4 +83,3 @@ in
   };
 
 }
-

pkgs/shells/xonsh/default.nix

@@ -1,12 +1,12 @@
 { lib
 , fetchFromGitHub
-, python3Packages
+, python3
 , glibcLocales
 , coreutils
 , git
 }:
 
-python3Packages.buildPythonApplication rec {
+python3.pkgs.buildPythonApplication rec {
   pname = "xonsh";
   version = "0.14.0";
 
@@ -29,16 +29,8 @@ python3Packages.buildPythonApplication rec {
     find scripts -name 'xonsh*' -exec sed -i -e "s|env -S|env|" {} \;
     find -name "*.xsh" | xargs sed -ie 's|/usr/bin/env|${coreutils}/bin/env|'
     patchShebangs .
-
-    substituteInPlace scripts/xon.sh \
-      --replace 'python' "${python3Packages.python}/bin/python"
-
   '';
 
-  makeWrapperArgs = [
-    "--prefix PYTHONPATH : ${placeholder "out"}/lib/${python3Packages.python.libPrefix}/site-packages"
-  ];
-
   disabledTests = [
     # fails on sandbox
     "test_colorize_file"
@@ -71,9 +63,9 @@ python3Packages.buildPythonApplication rec {
   '';
 
   nativeCheckInputs = [ glibcLocales git ] ++
-    (with python3Packages; [ pyte pytestCheckHook pytest-mock pytest-subprocess ]);
+    (with python3.pkgs; [ pyte pytestCheckHook pytest-mock pytest-subprocess ]);
 
-  propagatedBuildInputs = with python3Packages; [ ply prompt-toolkit pygments ];
+  propagatedBuildInputs = with python3.pkgs; [ ply prompt-toolkit pygments ];
 
   meta = with lib; {
     description = "A Python-ish, BASHwards-compatible shell";
@@ -85,5 +77,6 @@ python3Packages.buildPythonApplication rec {
 
   passthru = {
     shellPath = "/bin/xonsh";
+    python = python3;
   };
 }

pkgs/shells/xonsh/wrapper.nix

@@ -0,0 +1,24 @@
+{ runCommand
+, xonsh-unwrapped
+, lib
+, extraPackages ? (ps: [ ])
+}:
+
+let
+  xonsh = xonsh-unwrapped;
+  inherit (xonsh.passthru) python;
+
+  pythonEnv = python.withPackages (ps: [
+    (ps.toPythonModule xonsh)
+  ] ++ extraPackages ps);
+
+in
+runCommand "${xonsh.pname}-${xonsh.version}"
+{
+  inherit (xonsh) pname version meta passthru;
+} ''
+  mkdir -p $out/bin
+  for bin in ${lib.getBin xonsh}/bin/*; do
+    ln -s ${pythonEnv}/bin/$(basename "$bin") $out/bin/
+  done
+''

pkgs/top-level/all-packages.nix

@@ -14751,7 +14751,8 @@ with pkgs;
 
   rush = callPackage ../shells/rush { };
 
-  xonsh = callPackage ../shells/xonsh { };
+  xonsh = callPackage ../shells/xonsh/wrapper.nix { };
+  xonsh-unwrapped = callPackage ../shells/xonsh { };
 
   zsh = callPackage ../shells/zsh { };