Go the other way around again and use path instead of string

Author: tfc

documentation/docs/integration/flake-parts.md

@@ -30,7 +30,7 @@ A complete example looks like this:
       packages.default = pkgs.hello;
 
       # (3) point mkdocs-flake to your mkdocs root folder
-      documentation.mkdocs-root = "./docs";
+      documentation.mkdocs-root = ./docs;
 
       # (4) Build the docs:
       #     `nix build .#documentation`

flake.nix

@@ -101,7 +101,7 @@
             ];
           };
 
-          documentation.mkdocs-root = "./documentation";
+          documentation.mkdocs-root = ./documentation;
 
           packages = {
             default = config.packages.mkdocs;

modules/documentation.nix

@@ -4,13 +4,12 @@ let
   cfg = config.documentation;
 
   strict = lib.optionalString cfg.strict "--strict";
-  docsRoot = flakeSelf + "/" + cfg.mkdocs-root;
 in
 
 {
   options.documentation = {
     mkdocs-root = lib.mkOption {
-      type = lib.types.nullOr lib.types.str;
+      type = lib.types.nullOr lib.types.path;
       default = null;
       example = "./documentation";
       description = "Path to your mkdocs documentation project with mkdocs.yml. Relative from your flake.nix.";
@@ -33,7 +32,7 @@ in
 
   config = lib.mkIf (cfg.mkdocs-root != null) {
     packages.documentation = pkgs.runCommand "mkdocs-flake-documentation" {} ''
-      cd ${docsRoot}
+      cd ${cfg.mkdocs-root}
       ${cfg.mkdocs-package}/bin/mkdocs build ${strict} --site-dir $out
     '';
 
@@ -42,9 +41,10 @@ in
       program = pkgs.writeShellScriptBin "mkdocs-watch" ''
         set -euo pipefail
         if ! test -f mkdocs.yml; then
-          if test -f "${cfg.mkdocs-root}/mkdocs.yml"; then
-            echo "Your documentation is in ${cfg.mkdocs-root}. Switching into that folder."
-            cd "${cfg.mkdocs-root}"
+          rel_path=${lib.path.removePrefix (/. + (builtins.unsafeDiscardStringContext flakeSelf.outPath)) cfg.mkdocs-root}
+          if test -f "$rel_path/mkdocs.yml"; then
+            echo "Your documentation is in $rel_path. Switching into that folder."
+            cd "$rel_path"
           else
             echo "Can't find mkdocs.yml. Is your flake's `documentation.mkdocs-root` set correctly?"
           fi