clan-cli devShell: add editable install

pkgs/clan-cli/shell.nix

@@ -1,25 +1,49 @@
-{ nix-unit, clan-cli, ui-assets, system, mkShell, writeScriptBin, openssh }:
+{ nix-unit, clan-cli, ui-assets, system, mkShell, writeScriptBin, openssh, ruff, python3 }:
 let
   checkScript = writeScriptBin "check" ''
     nix build .#checks.${system}.{treefmt,clan-pytest} -L "$@"
   '';
+
+  pythonWithDeps = python3.withPackages (
+    ps:
+    clan-cli.propagatedBuildInputs
+    ++ clan-cli.devDependencies
+    ++ [
+      ps.pip
+    ]
+  );
 in
 mkShell {
   packages = [
     nix-unit
     openssh
+    ruff
     clan-cli.checkPython
   ];
 
   shellHook = ''
     tmp_path=$(realpath ./.direnv)
 
+    repo_root=$(realpath .)
+    mkdir -p "$tmp_path/python/${pythonWithDeps.sitePackages}"
+
+    # Install the package in editable mode
+    # This allows executing `clan` from within the dev-shell using the current
+    # version of the code and its dependencies.
+    ${pythonWithDeps.interpreter} -m pip install \
+      --quiet \
+      --disable-pip-version-check \
+      --no-index \
+      --no-build-isolation \
+      --prefix "$tmp_path/python" \
+      --editable $repo_root
+
     rm -f clan_cli/nixpkgs clan_cli/webui/assets
     ln -sf ${clan-cli.nixpkgs} clan_cli/nixpkgs
     ln -sf ${ui-assets} clan_cli/webui/assets
 
-    export PATH="$tmp_path/bin:${checkScript}/bin:$PATH"
-    export PYTHONPATH="$PYTHONPATH:$(pwd)"
+    export PATH="$tmp_path/python/bin:${checkScript}/bin:$PATH"
+    export PYTHONPATH="$repo_root:$tmp_path/python/${pythonWithDeps.sitePackages}:"
 
     export XDG_DATA_DIRS="$tmp_path/share''${XDG_DATA_DIRS:+:$XDG_DATA_DIRS}"
     export fish_complete_path="$tmp_path/share/fish/vendor_completions.d''${fish_complete_path:+:$fish_complete_path}"