foot: add module

Foot is a fast terminal emulator for Wayland. It can optionally be run
in a client-server configuration.

There are three unit tests to handle an empty configuration, the
default configuration, and systemd service file generation.

modules/programs/foot.nix

@@ -0,0 +1,77 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+
+  cfg = config.programs.foot;
+  iniFormat = pkgs.formats.ini { };
+
+in {
+  meta.maintainers = with lib.maintainers; [ plabadens ];
+
+  options.programs.foot = {
+    enable = mkEnableOption "Foot terminal";
+
+    package = mkOption {
+      type = types.package;
+      default = pkgs.foot;
+      defaultText = literalExample "pkgs.foot";
+      description = "The foot package to install";
+    };
+
+    server.enable = mkEnableOption "Foot terminal server";
+
+    settings = mkOption {
+      type = iniFormat.type;
+      default = { };
+      description = ''
+        Configuration written to
+        <filename>$XDG_CONFIG_HOME/foot/foot.ini</filename>. See <link
+        xlink:href="https://codeberg.org/dnkl/foot/src/branch/master/foot.ini"/>
+        for a list of available options.
+      '';
+      example = literalExample ''
+        {
+          main = {
+            term = "xterm-256color";
+
+            font = "Fira Code:size=11";
+            dpi-aware = "yes";
+          };
+
+          mouse = {
+            hide-when-typing = "yes";
+          };
+        }
+      '';
+    };
+  };
+
+  config = mkIf cfg.enable {
+    home.packages = [ cfg.package ];
+
+    xdg.configFile."foot/foot.ini" = mkIf (cfg.settings != { }) {
+      source = iniFormat.generate "foot.ini" cfg.settings;
+    };
+
+    systemd.user.services = mkIf cfg.server.enable {
+      foot = {
+        Unit = {
+          Description =
+            "Fast, lightweight and minimalistic Wayland terminal emulator.";
+          Documentation = "man:foot(1)";
+          PartOf = [ "graphical-session.target" ];
+          After = [ "graphical-session.target" ];
+        };
+
+        Service = {
+          ExecStart = "${cfg.package}/bin/foot --server";
+          Restart = "on-failure";
+        };
+
+        Install = { WantedBy = [ "graphical-session.target" ]; };
+      };
+    };
+  };
+}