From 61475c4779cd0327919ecc2e6f45df08a403d73c Mon Sep 17 00:00:00 2001
From: Robert Helgesson <robert@rycee.net>
Date: Wed, 3 Feb 2021 23:24:43 +0100
Subject: [PATCH] experiment

---
 modules/home-environment.nix                    |  2 +-
 modules/lib/shell.nix                           | 17 +++++++++++++++++
 .../session-variables-explicit.nix              |  8 ++++----
 3 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/modules/home-environment.nix b/modules/home-environment.nix
index 85d18f63a..4e437ce9c 100644
--- a/modules/home-environment.nix
+++ b/modules/home-environment.nix
@@ -479,7 +479,7 @@ in
             if [ -n "$__HM_SESS_VARS_SOURCED" ]; then return; fi
             export __HM_SESS_VARS_SOURCED=1
 
-            ${config.lib.shell.exportAll cfg.sessionVariables}
+            ${config.lib.shell.exportAll' { colonVars = ["NIX_PATH" "PATH"]; } cfg.sessionVariables}
           '' + lib.optionalString (cfg.sessionPath != [ ]) ''
             export PATH="$PATH''${PATH:+:}${concatStringsSep ":" cfg.sessionPath}"
           '' + cfg.sessionVariablesExtra;
diff --git a/modules/lib/shell.nix b/modules/lib/shell.nix
index 5e5743f51..cba97f476 100644
--- a/modules/lib/shell.nix
+++ b/modules/lib/shell.nix
@@ -4,8 +4,25 @@ rec {
   # Produces a Bourne shell like variable export statement.
   export = n: v: ''export ${n}="${toString v}"'';
 
+  export' = { colonVars ? [ ] }:
+    n: v:
+    let
+      replaceMatch = match:
+        lib.replaceStrings [ ":\$${match}:" ":\$${match}" "\$${match}:" ] [
+          "\${${match}:+:\$${match}:}"
+          "\${${match}:+:\$${match}}"
+          "\${${match}:+\$${match}:}"
+        ];
+
+      mkValue = n: v:
+        if builtins.elem n colonVars then replaceMatch n v else toString v;
+    in ''export ${n}="${mkValue n v}"'';
+
   # Given an attribute set containing shell variable names and their
   # assignment, this function produces a string containing an export
   # statement for each set entry.
   exportAll = vars: lib.concatStringsSep "\n" (lib.mapAttrsToList export vars);
+
+  exportAll' = opts: vars:
+    lib.concatStringsSep "\n" (lib.mapAttrsToList (export' opts) vars);
 }
diff --git a/tests/modules/home-environment/session-variables-explicit.nix b/tests/modules/home-environment/session-variables-explicit.nix
index 8ee540716..2e74b4dac 100644
--- a/tests/modules/home-environment/session-variables-explicit.nix
+++ b/tests/modules/home-environment/session-variables-explicit.nix
@@ -13,8 +13,8 @@ let
     export __HM_SESS_VARS_SOURCED=1
 
     export LOCALE_ARCHIVE_2_27="${pkgs.glibcLocales}/lib/locale/locale-archive"
-    export NIX_PATH="testpath=$HOME/testpath:$NIX_PATH"
-    export PATH="$PATH:$HOME/bin"
+    export NIX_PATH="testpath=$HOME/testpath''${NIX_PATH:+:$NIX_PATH}"
+    export PATH="''${PATH:+$PATH:}$HOME/bin"
     export XDG_CACHE_HOME="/home/hm-user/.cache"
     export XDG_CONFIG_HOME="/home/hm-user/.config"
     export XDG_DATA_HOME="/home/hm-user/.local/share"
@@ -25,8 +25,8 @@ let
     if [ -n "$__HM_SESS_VARS_SOURCED" ]; then return; fi
     export __HM_SESS_VARS_SOURCED=1
 
-    export NIX_PATH="testpath=$HOME/testpath:$NIX_PATH"
-    export PATH="$PATH:$HOME/bin"
+    export NIX_PATH="testpath=$HOME/testpath''${NIX_PATH:+:$NIX_PATH}"
+    export PATH="''${PATH:+$PATH:}$HOME/bin"
     export XDG_CACHE_HOME="/home/hm-user/.cache"
     export XDG_CONFIG_HOME="/home/hm-user/.config"
     export XDG_DATA_HOME="/home/hm-user/.local/share"