vte: add module

This abstracts out the VTE setup from the gnome-terminal module into
its own module and options.

modules/misc/vte.nix

@@ -0,0 +1,51 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+{
+  meta.maintainers = [ maintainers.rycee ];
+
+  options.programs = let
+    description = ''
+      Whether to enable integration with terminals using the VTE
+      library. This will let the terminal track the current working
+      directory.
+    '';
+  in {
+    bash.enableVteIntegration = mkEnableOption "" // { inherit description; };
+
+    zsh.enableVteIntegration = mkEnableOption "" // { inherit description; };
+  };
+
+  config = mkMerge [
+    (mkIf config.programs.bash.enableVteIntegration {
+      # Unfortunately we have to do a little dance here to fix two
+      # problems with the upstream vte.sh file:
+      #
+      #  - It does `PROMPT_COMMAND="__vte_prompt_command"` which
+      #    clobbers any previously assigned prompt command.
+      #
+      #  - Its `__vte_prompt_command` function runs commands that will
+      #    overwrite the exit status of the command the user ran.
+      programs.bash.initExtra = ''
+        __HM_PROMPT_COMMAND="''${PROMPT_COMMAND:+''${PROMPT_COMMAND%;};}__hm_vte_prompt_command"
+        . ${pkgs.vte}/etc/profile.d/vte.sh
+        if [[ $(type -t __vte_prompt_command) = function ]]; then
+          __hm_vte_prompt_command() {
+            local old_exit_status=$?
+            __vte_prompt_command
+            return $old_exit_status
+          }
+          PROMPT_COMMAND="$__HM_PROMPT_COMMAND"
+        fi
+        unset __HM_PROMPT_COMMAND
+      '';
+    })
+
+    (mkIf config.programs.zsh.enableVteIntegration {
+      programs.zsh.initExtra = ''
+        . ${pkgs.vte}/etc/profile.d/vte.sh
+      '';
+    })
+  ];
+}