fish: unify NixOS and Home Manager configurations (#2108)

Link: https://github.com/nix-community/stylix/pull/2108

Reviewed-by: 0xda157 <da157@voidq.com>
Reviewed-by: NAHO <90870942+trueNAHO@users.noreply.github.com>

modules/fish/hm.nix

@@ -1,10 +1 @@
-{ mkTarget, ... }:
-mkTarget {
-  config =
-    { colors, inputs }:
-    {
-      programs.fish.interactiveShellInit = import ./prompt.nix {
-        inherit colors inputs;
-      };
-    };
-}
+import ./shared.nix

modules/fish/nixos.nix

@@ -1,8 +1 @@
-{ mkTarget, ... }:
-mkTarget {
-  config =
-    { colors, inputs }:
-    {
-      programs.fish.promptInit = import ./prompt.nix { inherit colors inputs; };
-    };
-}
+import ./shared.nix

modules/fish/prompt.nix

@@ -1,12 +0,0 @@
-{ colors, inputs }:
-let
-  theme = colors { templateRepo = inputs.base16-fish; };
-in
-''
-  source ${theme}
-
-  # See https://github.com/tomyun/base16-fish/issues/7 for why this condition exists
-  if status --is-interactive && test -z "$TMUX"
-    base16-${colors.slug}
-  end
-''

modules/fish/shared.nix

@@ -0,0 +1,19 @@
+{ mkTarget, ... }:
+mkTarget {
+  config =
+    { colors, inputs }:
+    {
+      programs.fish.interactiveShellInit =
+        let
+          theme = colors { templateRepo = inputs.base16-fish; };
+        in
+        ''
+          source ${theme}
+
+          # See https://github.com/tomyun/base16-fish/issues/7 for why this condition exists
+          if test -z $TMUX
+            base16-${colors.slug}
+          end
+        '';
+    };
+}