Universal-Debloater-Alliance/universal-android-debloater-next-generation · critical

Can't detect cache dir

Error message

Can't detect cache dir

What it means

At startup, main builds the global CACHE_DIR via `dirs::cache_dir().expect("Can't detect cache dir")`. dirs::cache_dir returns None when the platform's cache-directory convention cannot be resolved (e.g. $XDG_CACHE_HOME unset and $HOME unavailable on Linux). The app treats an unresolvable cache dir as fatal and panics before the GUI starts.

Solutions

1. Set the environment before launching: `XDG_CACHE_HOME=/tmp/uad-cache` or ensure `HOME` points at a writable directory (`env HOME=/root ./uad-ng`).
2. Fall back to a default (e.g. ./cache or temp_dir()) instead of panicking when dirs::cache_dir() is None.
3. When running as a service, configure the unit with `Environment=HOME=/home/user` or use `ExecStart=/usr/bin/env HOME=%h ...`.
4. Log the resolved cache path at startup to make misconfiguration visible.

Example fix

// before
static CACHE_DIR: LazyLock<PathBuf> = LazyLock::new(|| {
    setup_uad_dir(&dirs::cache_dir().expect("Can't detect cache dir"))
});
// after
static CACHE_DIR: LazyLock<PathBuf> = LazyLock::new(|| {
    setup_uad_dir(&dirs::cache_dir().unwrap_or_else(|| {
        std::env::temp_dir().join("uad-ng")
    }))
});

// before launching the app
const HOME: &str = "HOME";
const XDG: &str = "XDG_CACHE_HOME";
if std::env::var_os(XDG).is_none()
    && std::env::var_os(HOME).map_or(true, |h| h.is_empty())
{
    eprintln!("HOME/XDG_CACHE_HOME unset: cache dir cannot be detected");
}

let cache = dirs::cache_dir().unwrap_or_else(|| std::env::temp_dir().join("uad-ng"));

When it happens

Trigger: Launching the UAD GUI binary in an environment where dirs::cache_dir() yields None: Linux with $HOME unset (cron, systemd service without User= env, su without login shell, minimal containers), or a Windows profile without a LOCALAPPDATA equivalent.

Common situations: Running the app from a systemd unit or Docker container that doesn't set HOME/XDG_CACHE_HOME; invoking via `sudo -i` strips or alters env; headless CI environments launching the GUI binary for smoke tests.

Understand the failure class

Background: "environment variable is not set" and "Missing keys in environment" errors: what missing required env var messages mean and how to fix them — this error's family across 28 libraries.

Related errors

• Can't detect config dir
• Can't detect cache dir
• setup logging
• {e}
• There must be 1 tab after serial

AI-assisted analysis of Universal-Debloater-Alliance/universal-android-debloater-next-generation@64465c850c (2026-09-12). Data as JSON: /api/errors/9ff5f790eb67d878. Report an issue: GitHub.

Appendix: source

Thrown at crates/uad-gui/src/main.rs:15

#![windows_subsystem = "windows"]

use fern::{
    FormatCallback,
    colors::{Color, ColoredLevelConfig},
};
use log::Record;
use std::sync::LazyLock;
use std::{fmt::Arguments, fs::OpenOptions, path::PathBuf};
use uad_core::utils::setup_uad_dir;

use uad_gui::gui::UadGui;

static CACHE_DIR: LazyLock<PathBuf> =
    LazyLock::new(|| setup_uad_dir(&dirs::cache_dir().expect("Can't detect cache dir")));

fn main() -> iced::Result {
    // Safety: This function is safe to call in a single-threaded program.
    // The exact requirement is: you must ensure that there are no other threads concurrently writing or
    // reading(!) the environment through functions or global variables other than the ones in this module.
    unsafe {
        // Force WGPU/Iced to use discrete GPU to prevent crashes on PCs with two GPUs.
        // See #848 and related pull 850.
        std::env::set_var("WGPU_POWER_PREF", "high");
    }

    setup_logger().expect("setup logging");
    UadGui::start()
}

/// Sets up logging to a new file in `CACHE_DIR"/uadng.log"`
/// Also attaches the terminal on Windows machines
/// '''

View on GitHub (pinned to 64465c850c)