From d4aa5ceed0e191e216c76aaf51239749448dac6a Mon Sep 17 00:00:00 2001
From: Yuval Kogman <nothingmuch@woobling.org>
Date: Thu, 11 Dec 2025 17:03:44 +0100
Subject: [PATCH] Specify --tree-root to treefmt flake check

Since the .git directory is filtered out of the the src files in the
sandboxed build, treefmt incorrectly identifies /nix/store as the
project root and attempts to format readonly files there

Specifying `--tree-root .` (will be `/build/source` in the sandbox
container) ensures that only the project files are formatted as
expected.
---
 flake.nix | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/flake.nix b/flake.nix
index 077b90537..c85e5e588 100644
--- a/flake.nix
+++ b/flake.nix
@@ -210,7 +210,7 @@
             src = pkgs.lib.sources.sourceFilesBySuffices ./. [ ".nix" ];
             nativeBuildInputs = [ pkgs.nixfmt-tree ];
             checkPhase = ''
-              treefmt --ci
+              treefmt --ci --tree-root .
             '';
           };