fish: add command option for abbreviations (#6666)

The fish shell has added a flag to the abbr command which allows one to expand it only if it is typed after a real command e.g.:
git s -> git status
s -> s

Also see the last example here: https://fishshell.com/docs/current/cmds/abbr.html#examples

modules/programs/fish.nix

@@ -167,6 +167,16 @@ let
         '';
       };
 
+      command = mkOption {
+        type = with types; nullOr str;
+        default = null;
+        description = ''
+          Specifies the command(s) for which the abbreviation should expand. If
+          set, the abbreviation will only expand when used as an argument to
+          the given command(s).
+        '';
+      };
+
       setCursor = mkOption {
         type = with types; (either bool str);
         default = false;
@@ -201,7 +211,7 @@ let
               (lib.generators.mkValueStringDefault { } v)
             ];
         } {
-          inherit position regex function;
+          inherit position regex command function;
           set-cursor = setCursor;
         };
       modifiers = if isAttrs def then mods else "";

tests/modules/programs/fish/abbrs.nix

@@ -34,6 +34,10 @@
             end
           '';
         };
+        co = {
+          command = "git";
+          expansion = "checkout";
+        };
         dotdot = {
           regex = "^\\.\\.+$";
           function = "multicd";
@@ -64,6 +68,8 @@
           cd ..
         end
         '"
+        assertFileContains home-files/.config/fish/config.fish \
+          "abbr --add --command git -- co checkout"
         assertFileContains home-files/.config/fish/config.fish \
           "abbr --add --function multicd --regex '^\.\.+$' -- dotdot"
       '';