Add nix shell detection to tide

home/fish/fish.nix

@@ -1,10 +1,17 @@
 { config, pkgs, ... }:
 
 {
+  imports = [
+    ./tide/nix-shell.nix
+  ];
+
   programs.fish = {
     enable = true;
     package = pkgs.unstable.fish;
-        functions = {
+    functions = { };
+
+    tide = {
+      nix-shell.enable = true;
     };
 
     shellAliases = {
@@ -18,6 +25,13 @@
       today = "date +%F";
     };
 
+    shellInit = ''
+      # Source brew integration
+      if test -e /opt/homebrew/bin/brew
+        /opt/homebrew/bin/brew shellenv | source
+      end
+    '';
+
     interactiveShellInit = ''
       set fish_greeting
 

home/fish/tide/nix-shell.nix

@@ -0,0 +1,21 @@
+{ config, pkgs, lib, ... }:
+
+with lib;
+let
+  cfg = config.programs.fish.tide.nix-shell;
+in
+{
+  options.programs.fish.tide.nix-shell = {
+    enable = mkEnableOption "An indicator of having a `nix shell` environment";
+  };
+
+  config.programs.fish = mkIf cfg.enable {
+    functions._tide_item_nix_shell = ''
+      if string match -q "/nix/store/*" $PATH
+        set -U tide_nix_shell_color blue
+        set -U tide_nix_shell_bg_color normal
+        _tide_print_item nix_shell "❄"
+      end
+    '';
+  };
+}