Merge PR #1211

.github/workflows/nix.yml

@@ -0,0 +1,28 @@
+# Evaluates the Nix flake (no build, about a minute): `nix build` / `nix develop` stop at evaluation
+# when Cargo.lock gains something nix/package.nix can't vendor, and nothing else would notice.
+name: Nix
+
+on:
+  push:
+    branches: [main]
+    paths: ["flake.nix", "flake.lock", "nix/**", "Cargo.lock", ".github/workflows/nix.yml"]
+  pull_request:
+    paths: ["flake.nix", "flake.lock", "nix/**", "Cargo.lock", ".github/workflows/nix.yml"]
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+concurrency:
+  group: nix-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  eval:
+    runs-on: ubuntu-latest
+    timeout-minutes: 15
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: cachix/install-nix-action@13d8dd58da0234aa297dedd986986ccb8e7f3e24 # v31.11.1
+      - name: nix flake check --no-build
+        run: nix flake check --no-build --all-systems

AGENTS.md

@@ -131,8 +131,8 @@ of it. Full standard: `../craftrules/standards/never-crash.md`
 → `ui-egui`, `mcp` (L5) → apps `lightcraft` (desktop), `lightcraft-cli` (render/commands/MCP). `scenes` generates demo
 photos. `xtask` = tooling (`ci`, `layers`, `assets`, `parity`, `wasm`, `corpus`, `stats`). `flake.nix` +
 `nix/package.nix` = the Nix package (`nix build` builds both binaries with the craft-fonts input, installs the
-desktop file/icons/AppStream metadata and runs `cargo test --workspace`; `nix develop` = dev shell). Community-maintained and not
-in CI: it may lag behind the workspace; see README → Quick start.
+desktop file/icons/AppStream metadata and runs `cargo test --workspace`; `nix develop` = dev shell). Community-maintained; CI only
+evaluates it (`.github/workflows/nix.yml`), so the build may lag behind the workspace; see README → Quick start.
 
 ## Contributor credits (About window)
 

CLAUDE.md

@@ -139,5 +139,5 @@ of it. Full standard: `../craftrules/standards/never-crash.md`
 → `ui-egui`, `mcp` (L5) → apps `lightcraft` (desktop), `lightcraft-cli` (render/commands/MCP). `scenes` generates demo
 photos. `xtask` = tooling (`ci`, `layers`, `assets`, `parity`, `wasm`, `corpus`, `stats`). `flake.nix` +
 `nix/package.nix` = the Nix package (`nix build` builds both binaries with the craft-fonts input, installs the
-desktop file/icons/AppStream metadata and runs `cargo test --workspace`; `nix develop` = dev shell). Community-maintained and not
-in CI: it may lag behind the workspace; see README → Quick start.
+desktop file/icons/AppStream metadata and runs `cargo test --workspace`; `nix develop` = dev shell). Community-maintained; CI only
+evaluates it (`.github/workflows/nix.yml`), so the build may lag behind the workspace; see README → Quick start.

apps/lightcraft/src/appearance.rs

@@ -51,7 +51,7 @@ fn decode(code: u32) -> Option<egui::Theme> {
 /// absolute path, and is never repeated.
 #[cfg(target_os = "linux")]
 fn gtk_theme() -> Option<egui::Theme> {
-    let exe = ["/usr/bin/gsettings", "/bin/gsettings", "/usr/local/bin/gsettings"].into_iter().find(|p| std::path::Path::new(p).is_file())?;
+    let exe = gsettings_exe(std::env::var_os("PATH").as_deref())?;
     let output = std::process::Command::new(exe).args(["get", "org.gnome.desktop.interface", "color-scheme"]).output().ok()?;
     if !output.status.success() {
         return None;
@@ -59,6 +59,15 @@ fn gtk_theme() -> Option<egui::Theme> {
     parse_gtk_scheme(std::str::from_utf8(&output.stdout).ok()?)
 }
 
+/// `gsettings` by absolute path: the absolute `PATH` entries first (NixOS has no /usr/bin/gsettings),
+/// then the usual places for a sparse `PATH`. Relative entries are skipped, so nothing runs from
+/// the working folder.
+#[cfg(target_os = "linux")]
+fn gsettings_exe(path: Option<&std::ffi::OsStr>) -> Option<std::path::PathBuf> {
+    let listed = path.map(std::env::split_paths).into_iter().flatten().filter(|dir| dir.is_absolute());
+    listed.chain(["/usr/bin", "/bin", "/usr/local/bin"].map(std::path::PathBuf::from)).map(|dir| dir.join("gsettings")).find(|exe| exe.is_file())
+}
+
 #[cfg(target_os = "linux")]
 fn parse_gtk_scheme(s: &str) -> Option<egui::Theme> {
     match s.trim().trim_matches('\'') {
@@ -174,6 +183,24 @@ mod tests {
         assert_eq!(calls.load(Ordering::Relaxed), after_settle);
     }
 
+    /// NixOS keeps `gsettings` in /run/current-system/sw/bin or the per-user profile: it is found
+    /// on `PATH`, but never through a relative entry, even one that leads to a real file.
+    #[cfg(target_os = "linux")]
+    #[test]
+    fn gsettings_is_found_on_absolute_path_entries_only() {
+        let dir = std::env::temp_dir().join(format!("lightcraft-gsettings-{}", std::process::id()));
+        std::fs::create_dir_all(&dir).unwrap();
+        std::fs::write(dir.join("gsettings"), "").unwrap();
+        let path = std::env::join_paths([std::path::Path::new("relative/bin"), &dir]).unwrap();
+        assert_eq!(super::gsettings_exe(Some(&path)), Some(dir.join("gsettings")));
+        let cwd = std::env::current_dir().unwrap();
+        let relative = std::path::PathBuf::from("../".repeat(cwd.components().count() - 1)).join(dir.strip_prefix("/").unwrap());
+        assert!(relative.join("gsettings").is_file());
+        let found = super::gsettings_exe(Some(relative.as_os_str()));
+        assert!(found.as_ref().is_none_or(|p| p.is_absolute()), "{found:?}");
+        let _ = std::fs::remove_dir_all(&dir);
+    }
+
     #[cfg(target_os = "linux")]
     #[test]
     fn portal_values_and_gsettings_output_decode() {