fish: augment run and shell with -u params (unstable)

homes/julian/features/fish/default.nix

@@ -67,14 +67,28 @@ with lib; {
         cd $argv
       '';
       run = ''
-        nix run --impure nixpkgs#"$argv[1]" -- $argv[2..-1]
+        set -l channel nixpkgs
+
+        if test "$argv[1]" = -u -o "$argv[1]" = --unstable
+            set channel github:NixOS/nixpkgs/nixpkgs-unstable
+            set -e argv[1]
+        end
+        nix run --impure $channel#"$argv[1]" -- $argv[2..-1]
       '';
       shell = ''
-        set args
+        set -l channel nixpkgs
-        for arg in $argv
+
-            set args $args nixpkgs#$arg
+        if test "$argv[1]" = -u -o "$argv[1]" = --unstable
+            set channel github:NixOS/nixpkgs/nixpkgs-unstable
+            set -e argv[1]
         end
-        nix shell --impure $args
+
+        set -l packages
+        for arg in $argv
+            set -a packages $channel#$arg
+        end
+
+        nix shell --impure $packages
       '';
       fish_user_key_bindings = ''
         bind ctrl-space 'zi; commandline -f repaint'