feat(nginx): etag from root drv path

modules/nixos/nginx/cache.nix

@@ -0,0 +1,63 @@
+let
+  locationModule = {
+    config,
+    virtualHost,
+    gensokyo-zone,
+    lib,
+    ...
+  }: let
+    inherit (lib.options) mkOption;
+    inherit (lib.modules) mkIf mkMerge mkOptionDefault;
+    inherit (lib.strings) hasPrefix removePrefix;
+    cfg = config.cache;
+  in {
+    options.cache = with lib.types; {
+      rootETag = mkOption {
+        type = bool;
+      };
+    };
+    config = let
+      rootStoreDir = removePrefix "${builtins.storeDir}/" config.root;
+    in {
+      cache = {
+        rootETag = mkOptionDefault (config.root != null && hasPrefix builtins.storeDir "${config.root}");
+      };
+      extraConfig = let
+        # TODO: should use ${rootStoreDir} or strip store prefix from $request_filename
+        rootETag = ''
+          etag off;
+          add_header etag '"$request_filename"';
+        '';
+      in
+        mkMerge [
+          (mkIf (cfg.rootETag && config.root != null) rootETag)
+        ];
+    };
+  };
+  hostModule = {
+    config,
+    lib,
+    ...
+  }: let
+    inherit (lib.options) mkOption;
+  in {
+    # TODO: config.root exists too!
+    options = with lib.types; {
+      locations = mkOption {
+        type = attrsOf (submoduleWith {
+          modules = [locationModule];
+          shorthandOnlyDefinesConfig = true;
+        });
+      };
+    };
+  };
+in
+  {lib, ...}: let
+    inherit (lib.options) mkOption;
+  in {
+    options.services.nginx = with lib.types; {
+      virtualHosts = mkOption {
+        type = attrsOf (submodule [hostModule]);
+      };
+    };
+  }