nixos/tarsnap, nixos/neo4j: defaultText for submodule options

unfortunately we don't have a good way to represent defaults that
reference other values of the current submodule, so we just use the
relative path of the referenced value and assume that the submodule was
declared as `rec`.

nixos/modules/services/backup/tarsnap.nix

@@ -60,7 +60,7 @@ in
       };
 
       archives = mkOption {
-        type = types.attrsOf (types.submodule ({ config, ... }:
+        type = types.attrsOf (types.submodule ({ config, options, ... }:
           {
             options = {
               keyfile = mkOption {
@@ -89,6 +89,9 @@ in
               cachedir = mkOption {
                 type = types.nullOr types.path;
                 default = "/var/cache/tarsnap/${utils.escapeSystemdPath config.keyfile}";
+                defaultText = literalExpression ''
+                  "/var/cache/tarsnap/''${utils.escapeSystemdPath config.${options.keyfile}}"
+                '';
                 description = ''
                   The cache allows tarsnap to identify previously stored data
                   blocks, reducing archival time and bandwidth usage.

nixos/modules/services/databases/neo4j.nix

@@ -437,6 +437,7 @@ in {
           baseDirectory = mkOption {
             type = types.path;
             default = "${cfg.directories.certificates}/${name}";
+            defaultText = literalExpression ''"''${config.${opt.directories.certificates}}/''${name}"'';
             description = ''
               The mandatory base directory for cryptographic objects of this
               policy. This path is only automatically generated when this
@@ -498,6 +499,7 @@ in {
           revokedDir = mkOption {
             type = types.path;
             default = "${config.baseDirectory}/revoked";
+            defaultText = literalExpression ''"''${config.${options.baseDirectory}}/revoked"'';
             description = ''
               Path to directory of CRLs (Certificate Revocation Lists) in
               PEM format. Must be an absolute path. The existence of this
@@ -533,6 +535,7 @@ in {
           trustedDir = mkOption {
             type = types.path;
             default = "${config.baseDirectory}/trusted";
+            defaultText = literalExpression ''"''${config.${options.baseDirectory}}/trusted"'';
             description = ''
               Path to directory of X.509 certificates in PEM format for
               trusted parties. Must be an absolute path. The existence of this