proton-drive-linux/crates/pdfs-core/src/config.rs

//! Static client identity and per-user filesystem paths.

use std::path::{Path, PathBuf};

use directories::ProjectDirs;
use serde::{Deserialize, Serialize};

use crate::error::{Error, Result};
use crate::menu::PromptConfig;
use crate::opener::OpenWith;
use crate::syncignore::DEFAULT_IGNORE_PATTERNS;

/// Proton requires `external-drive-{name}@{semver}-{channel}` (channel ∈
/// stable/beta/alpha); a malformed value trips the 422 anti-abuse path.
pub const APP_VERSION: &str = "external-drive-linux@0.1.0-alpha";
pub const USER_AGENT: &str = "proton-drive-linux/0.1.0";

/// Keyring service name; one entry per credential kind keyed by username.
pub const KEYRING_SERVICE: &str = "proton-drive-linux";

/// Default soft cap on the on-disk content cache (5 GiB). LRU-evicts unpinned
/// blobs back under this; pinned files are exempt. See [`crate::cache`].
pub const DEFAULT_CACHE_BUDGET_BYTES: u64 = 5 * 1024 * 1024 * 1024;

/// Environment override for [`AppConfig::resolved_conflict_sweep`]. Exists so a
/// support case can disable the sweep without editing the config file or
/// reinstalling — it wins over the stored setting.
pub const CONFLICT_SWEEP_ENV: &str = "PDFS_CONFLICT_SWEEP";

/// What the background conflict sweep (`pdfs-fuse`'s `pdfs-conflict-sweep`
/// thread) is allowed to do about a `(sync-conflict …)` copy it believes is a
/// redundant duplicate.
///
/// Defaults to [`SweepMode::Report`]: the sweep's whole reason to exist is that
/// the *previous* revision-identity check was wrong (B69), so the replacement is
/// not trusted with deletion until it has a release cycle of field evidence
/// behind it. See `docs/BUGS.md` B71.
#[derive(Serialize, Deserialize, Debug, Clone, Copy, PartialEq, Eq, Default)]
#[serde(rename_all = "lowercase")]
pub enum SweepMode {
    /// Do not run the sweep at all — the thread is never spawned.
    Off,
    /// Run, and log what it *would* remove, but never trash anything. Divergent
    /// and orphaned copies are still surfaced to the activity feed as usual.
    #[default]
    Report,
    /// Trash copies proven identical to their live sibling.
    Enforce,
}

impl SweepMode {
    /// Parse an operator-supplied value ([`CONFLICT_SWEEP_ENV`] or a CLI flag).
    /// `None` for anything unrecognised, so a typo falls back to the stored
    /// setting rather than silently picking a mode the operator did not ask for.
    pub fn parse(value: &str) -> Option<Self> {
        match value.trim().to_ascii_lowercase().as_str() {
            "off" | "no" | "false" | "0" | "disabled" => Some(Self::Off),
            "report" | "dry-run" | "dryrun" | "observe" => Some(Self::Report),
            "enforce" | "on" | "yes" | "true" | "1" => Some(Self::Enforce),
            _ => None,
        }
    }

    /// Whether this mode is allowed to trash a duplicate.
    pub fn is_enforcing(self) -> bool {
        matches!(self, Self::Enforce)
    }
}

/// Precedence for [`AppConfig::resolved_conflict_sweep`], split out from the
/// environment read so it can be unit-tested without mutating process state.
fn resolve_sweep_mode(env: Option<&str>, stored: Option<SweepMode>) -> SweepMode {
    env.and_then(SweepMode::parse)
        .or(stored)
        .unwrap_or_default()
}

/// Configuration structure allowing the user to customize client identification headers.
#[derive(Serialize, Deserialize, Debug, Clone)]
pub struct AppConfig {
    pub app_version: String,
    pub user_agent: String,
    /// Soft cap on the on-disk content cache, in bytes (`0` = unlimited).
    /// `None` means "use [`DEFAULT_CACHE_BUDGET_BYTES`]"; the Settings page
    /// writes an explicit value here. Defaulted for configs predating the field.
    #[serde(default)]
    pub cache_budget: Option<u64>,
    /// Upload cap in bytes per second shared by every upload. `None` or `0`
    /// means no cap. Defaulted for configs predating the field.
    #[serde(default)]
    pub upload_limit: Option<u64>,
    /// Download cap in bytes per second shared by every download, FUSE reads
    /// included. `None` or `0` means no cap. Defaulted for configs predating
    /// the field.
    #[serde(default)]
    pub download_limit: Option<u64>,
    /// Mountpoint the daemon mounts at. `None` means
    /// [`AppDirs::default_mountpoint`]; the Settings page writes an explicit
    /// path here. Defaulted for configs predating the field.
    #[serde(default)]
    pub mountpoint: Option<String>,
    /// Ignore patterns (gitignore syntax) applied to every mirror sync folder,
    /// on top of each folder's own `.pdfsignore`. `None` means "use
    /// [`DEFAULT_IGNORE_PATTERNS`]"; an explicit empty list disables the
    /// defaults. Defaulted for configs predating the field.
    #[serde(default)]
    pub ignore_patterns: Option<Vec<String>>,
    /// Device uid this machine has been *adopted* into, overriding the hostname
    /// heuristic in `ensure_device`. Lives here rather than in `cache.db` so it
    /// survives a fresh install — on a new machine the DB is empty by
    /// definition, which is exactly when the pin matters. `None` means "resolve
    /// by hostname". Defaulted for configs predating the field.
    #[serde(default)]
    pub device_uid: Option<String>,
    /// What the background conflict sweep may do. `None` means "use
    /// [`SweepMode::default`]" (report-only). Defaulted for configs predating
    /// the field, and overridable at runtime via [`CONFLICT_SWEEP_ENV`].
    #[serde(default)]
    pub conflict_sweep: Option<SweepMode>,
    /// How files opened from the prompt/browser are launched. `None` means
    /// "hand everything to `xdg-open`", which is what the client did before
    /// this existed. See [`crate::opener`]. Defaulted for configs predating the
    /// field.
    #[serde(default)]
    pub open_with: Option<OpenWith>,
    /// `pdfs-prompt` behaviour, including the external launcher used by
    /// `--dmenu`. See [`crate::menu`]. Defaulted for configs predating the
    /// field.
    #[serde(default)]
    pub prompt: Option<PromptConfig>,
    /// Paint the desktop app in Proton purple instead of the system accent
    /// colour. `None` means "follow the system". Defaulted for configs
    /// predating the field.
    #[serde(default)]
    pub proton_accent: Option<bool>,
    /// How the desktop app's My Files page lays out and orders a folder.
    /// Defaulted for configs predating the field.
    #[serde(default)]
    pub files_view: FilesView,
    /// The user hid the tray icon from its own menu. The tray exits at start
    /// while this is set, and the app does not spawn it; Preferences turns it
    /// back on. Defaulted for configs predating the field.
    #[serde(default)]
    pub tray_hidden: bool,
}

/// The My Files page's view choices, remembered between runs.
#[derive(Serialize, Deserialize, Debug, Clone, Copy, PartialEq, Eq)]
#[serde(default)]
pub struct FilesView {
    /// Columns instead of the icon grid.
    pub list: bool,
    pub sort: FileSort,
    pub descending: bool,
    /// Folders ahead of files, whatever the sort.
    pub folders_first: bool,
}

impl Default for FilesView {
    fn default() -> Self {
        Self {
            list: false,
            sort: FileSort::Name,
            descending: false,
            folders_first: true,
        }
    }
}

/// The key a My Files listing is ordered by.
#[derive(Serialize, Deserialize, Debug, Clone, Copy, PartialEq, Eq, Default)]
#[serde(rename_all = "lowercase")]
pub enum FileSort {
    #[default]
    Name,
    Size,
    Modified,
}

impl FileSort {
    /// The name used in the desktop app's actions and the config file.
    pub fn as_str(self) -> &'static str {
        match self {
            FileSort::Name => "name",
            FileSort::Size => "size",
            FileSort::Modified => "modified",
        }
    }

    pub fn parse(value: &str) -> Option<Self> {
        match value {
            "name" => Some(FileSort::Name),
            "size" => Some(FileSort::Size),
            "modified" => Some(FileSort::Modified),
            _ => None,
        }
    }
}

impl Default for AppConfig {
    fn default() -> Self {
        Self {
            app_version: APP_VERSION.to_string(),
            user_agent: USER_AGENT.to_string(),
            cache_budget: None,
            upload_limit: None,
            download_limit: None,
            mountpoint: None,
            ignore_patterns: None,
            device_uid: None,
            conflict_sweep: None,
            open_with: None,
            prompt: None,
            proton_accent: None,
            files_view: FilesView::default(),
            tray_hidden: false,
        }
    }
}

impl AppConfig {
    /// The effective cache budget in bytes: the user's explicit choice, or
    /// [`DEFAULT_CACHE_BUDGET_BYTES`] when unset.
    pub fn resolved_cache_budget(&self) -> u64 {
        self.cache_budget.unwrap_or(DEFAULT_CACHE_BUDGET_BYTES)
    }

    /// The effective opener policy: the user's rules, or the all-`xdg-open`
    /// default. Cloned rather than borrowed because callers hold it for the
    /// life of a window, long after the config value is gone.
    pub fn resolved_open_with(&self) -> OpenWith {
        self.open_with.clone().unwrap_or_default()
    }

    /// The effective prompt settings, defaulted when the section is absent.
    pub fn resolved_prompt(&self) -> PromptConfig {
        self.prompt.clone().unwrap_or_default()
    }

    /// The effective conflict-sweep mode: the [`CONFLICT_SWEEP_ENV`] override if
    /// it parses, then the user's stored choice, then [`SweepMode::default`].
    ///
    /// The environment wins so a support case can stop a destructive background
    /// loop without editing config or reinstalling (`docs/BUGS.md` B71). An
    /// unparseable value is ignored rather than treated as "off", so a typo
    /// cannot silently change behaviour in either direction.
    pub fn resolved_conflict_sweep(&self) -> SweepMode {
        resolve_sweep_mode(
            std::env::var(CONFLICT_SWEEP_ENV).ok().as_deref(),
            self.conflict_sweep,
        )
    }

    /// The effective global sync ignore patterns: the user's explicit list, or
    /// [`DEFAULT_IGNORE_PATTERNS`] when unset. An explicit empty list is
    /// honoured as "no global patterns", which is why this is not a
    /// `unwrap_or_default`.
    pub fn resolved_ignore_patterns(&self) -> Vec<String> {
        match &self.ignore_patterns {
            Some(patterns) => patterns.clone(),
            None => DEFAULT_IGNORE_PATTERNS
                .iter()
                .map(|s| (*s).to_string())
                .collect(),
        }
    }
}

/// Resolved XDG locations for state, cache, and the default mountpoint.
pub struct AppDirs {
    dirs: ProjectDirs,
}

impl AppDirs {
    pub fn new() -> Result<Self> {
        let dirs = ProjectDirs::from("io", "narl", "proton-drive-linux")
            .ok_or_else(|| Error::Other("cannot resolve home directory".into()))?;
        Ok(Self { dirs })
    }

    /// Configuration file path (e.g. ~/.config/proton-drive-linux/config.json).
    pub fn config_path(&self) -> PathBuf {
        self.dirs.config_dir().join("config.json")
    }

    /// Load config from disk, creating default if missing.
    pub fn load_config(&self) -> AppConfig {
        let path = self.config_path();
        if path.exists() {
            match std::fs::read_to_string(&path)
                .map_err(Error::from)
                .and_then(|content| {
                    serde_json::from_str::<AppConfig>(&content).map_err(Error::from)
                }) {
                Ok(config) => return config,
                Err(e) => {
                    // Preserve the original bytes for diagnosis/recovery.  In
                    // particular, never replace a truncated config with defaults
                    // and silently lose mount, device, or ignore settings.
                    tracing::error!(path = %path.display(), error = %e, "config is unreadable; using in-memory defaults without overwriting it");
                    return AppConfig::default();
                }
            }
        }

        let default_config = AppConfig::default();
        if let Ok(content) = serde_json::to_string_pretty(&default_config) {
            let _ = std::fs::create_dir_all(self.dirs.config_dir());
            let _ = std::fs::write(&path, content);
        }
        default_config
    }

    /// Persist `config` to [`config_path`](Self::config_path), creating the
    /// config dir if missing. The Settings page calls this after editing the
    /// cache budget or mountpoint; the daemon re-reads the file on its next mount.
    pub fn save_config(&self, config: &AppConfig) -> Result<()> {
        let path = self.config_path();
        let parent = path
            .parent()
            .ok_or_else(|| Error::Other("configuration path has no parent".into()))?;
        std::fs::create_dir_all(parent)?;
        let nonce = std::time::SystemTime::now()
            .duration_since(std::time::UNIX_EPOCH)
            .map(|duration| duration.as_nanos())
            .unwrap_or(0);
        let tmp = path.with_extension(format!("json.tmp-{}-{nonce}", std::process::id()));
        use std::os::unix::fs::OpenOptionsExt as _;
        let mut file = std::fs::OpenOptions::new()
            .write(true)
            .create_new(true)
            .mode(0o600)
            .open(&tmp)?;
        use std::io::Write as _;
        file.write_all(&serde_json::to_vec_pretty(config)?)?;
        file.sync_all()?;
        std::fs::rename(&tmp, &path)?;
        std::fs::File::open(parent)?.sync_all()?;
        Ok(())
    }

    /// Persistent state: inode map / cache index DB lives here.
    pub fn state_dir(&self) -> PathBuf {
        // `state_dir` is Linux-only in `directories`; fall back to data dir.
        self.dirs
            .state_dir()
            .unwrap_or_else(|| self.dirs.data_dir())
            .to_path_buf()
    }

    /// Hydrated file-content cache.
    pub fn cache_dir(&self) -> PathBuf {
        self.dirs.cache_dir().to_path_buf()
    }

    /// Directory holding cached file-content blobs (pinned files).
    pub fn content_cache_dir(&self) -> PathBuf {
        self.cache_dir().join("content")
    }

    /// JSON pin registry, in persistent state (not the evictable cache).
    pub fn pins_path(&self) -> PathBuf {
        self.state_dir().join("pins.json")
    }

    /// Unified SQLite metadata cache (inodes, FTS, cache LRU, pins). Lives in
    /// persistent state next to `control.sock`; only the daemon writes it.
    pub fn db_path(&self) -> PathBuf {
        self.state_dir().join("cache.db")
    }

    /// Unix domain socket the mount daemon listens on for CLI control commands.
    pub fn control_socket(&self) -> PathBuf {
        self.state_dir().join("control.sock")
    }

    /// Unix domain socket the tray uses to ensure single instance.
    pub fn tray_socket(&self) -> PathBuf {
        self.state_dir().join("tray.sock")
    }

    /// The user's home directory — the root the daemon indexes for local
    /// (non-Drive) file search. `None` if it cannot be resolved.
    pub fn home_dir(&self) -> Option<PathBuf> {
        directories::UserDirs::new().map(|u| u.home_dir().to_path_buf())
    }

    /// Default mountpoint when the user does not pass one explicitly.
    pub fn default_mountpoint(&self) -> PathBuf {
        directories::UserDirs::new()
            .map(|u| u.home_dir().join("ProtonDrive"))
            .unwrap_or_else(|| PathBuf::from("/tmp/ProtonDrive"))
    }

    /// The effective mountpoint: the config's explicit path, or
    /// [`default_mountpoint`](Self::default_mountpoint) when unset.
    pub fn resolved_mountpoint(&self, config: &AppConfig) -> PathBuf {
        config
            .mountpoint
            .as_ref()
            .map(PathBuf::from)
            .unwrap_or_else(|| self.default_mountpoint())
    }

    /// Create state + cache dirs if missing, owner-only.
    ///
    /// The mode is set explicitly rather than left to the umask. These
    /// directories hold decrypted file content, a plaintext index of every node
    /// name in the Drive, and the control socket — and `create_dir_all` under a
    /// typical umask makes them `0755`. Until this was fixed, the only thing
    /// keeping another local user out was `~/.cache` and `~/.local/state`
    /// happening to be `0700`, which is a convention of the user's system and
    /// not something this client established (bugs.md B6).
    ///
    /// Applied on every start, not just at creation: a directory that already
    /// exists with a permissive mode — restored from a backup that flattened
    /// modes, or created by an older build — is tightened here.
    pub fn ensure(&self) -> Result<()> {
        for dir in [self.state_dir(), self.cache_dir()] {
            std::fs::create_dir_all(&dir)?;
            restrict_dir(&dir)?;
        }
        let config_dir = self.dirs.config_dir().to_path_buf();
        std::fs::create_dir_all(&config_dir)?;
        restrict_dir(&config_dir)?;
        Ok(())
    }
}

/// Make `dir` owner-only (`0700`). These directories contain decrypted bytes,
/// plaintext names, and an authenticated control socket, so failure is fatal.
fn restrict_dir(dir: &Path) -> Result<()> {
    use std::os::unix::fs::{MetadataExt as _, PermissionsExt};
    let before = std::fs::symlink_metadata(dir)?;
    if before.file_type().is_symlink() || !before.is_dir() {
        return Err(Error::Other(format!(
            "sensitive path is not a real directory: {}",
            dir.display()
        )));
    }
    if before.uid() != unsafe { libc::geteuid() } {
        return Err(Error::Other(format!(
            "sensitive directory is not owned by the current user: {}",
            dir.display()
        )));
    }
    std::fs::set_permissions(dir, std::fs::Permissions::from_mode(0o700))?;
    let after = std::fs::symlink_metadata(dir)?;
    if after.permissions().mode() & 0o777 != 0o700 {
        return Err(Error::Other(format!(
            "sensitive directory did not become owner-only: {}",
            dir.display()
        )));
    }
    Ok(())
}

/// Make a just-bound Unix socket owner-only (`0600`).
///
/// Connecting to the control socket drives the daemon with its authenticated
/// session — enumerate, read, upload, trash, share — without presenting any
/// credential, since the daemon already holds one. It is an authority boundary,
/// not merely private data, and `UnixListener::bind` applies the umask like any
/// other file (bugs.md B6).
///
/// There is a window between `bind` and this call during which the socket
/// carries the umask's mode. It is closed in practice by the containing
/// directory: [`Dirs::ensure`] has already made the state directory `0700`, so
/// nothing else can reach the socket to exploit the window.
pub fn restrict_socket(path: &Path) -> Result<()> {
    use std::os::unix::fs::PermissionsExt;
    std::fs::set_permissions(path, std::fs::Permissions::from_mode(0o600))?;
    Ok(())
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::os::unix::fs::PermissionsExt;

    fn mode_of(p: &Path) -> u32 {
        std::fs::metadata(p).unwrap().permissions().mode() & 0o777
    }

    /// bugs.md B6. A permissive mode here is not a cosmetic problem: these
    /// directories hold decrypted content, a plaintext index of every node name,
    /// and the control socket that commands the daemon's session.
    #[test]
    fn restrict_dir_makes_a_directory_owner_only() {
        let dir = std::env::temp_dir().join(format!(
            "pdfs-cfg-{}-{:?}",
            std::process::id(),
            std::thread::current().id()
        ));
        let _ = std::fs::remove_dir_all(&dir);
        std::fs::create_dir_all(&dir).unwrap();
        // Start deliberately world-readable, as `create_dir_all` under a typical
        // umask would leave it.
        std::fs::set_permissions(&dir, std::fs::Permissions::from_mode(0o755)).unwrap();

        restrict_dir(&dir).unwrap();

        assert_eq!(mode_of(&dir), 0o700, "group and other must have no access");
        let _ = std::fs::remove_dir_all(&dir);
    }

    #[test]
    fn restrict_dir_refuses_a_symlink() {
        let root = std::env::temp_dir().join(format!(
            "pdfs-cfg-link-{}-{:?}",
            std::process::id(),
            std::thread::current().id()
        ));
        let target = root.join("target");
        let link = root.join("state");
        std::fs::create_dir_all(&target).unwrap();
        std::os::unix::fs::symlink(&target, &link).unwrap();

        assert!(restrict_dir(&link).is_err());

        let _ = std::fs::remove_dir_all(&root);
    }

    /// Connecting to the control socket confers the daemon's authenticated
    /// session with no credential, so it is an authority boundary rather than
    /// merely private data.
    #[test]
    fn restrict_socket_makes_a_socket_owner_only() {
        let dir = std::env::temp_dir().join(format!(
            "pdfs-sock-{}-{:?}",
            std::process::id(),
            std::thread::current().id()
        ));
        let _ = std::fs::remove_dir_all(&dir);
        std::fs::create_dir_all(&dir).unwrap();
        let sock = dir.join("control.sock");
        // chmod semantics are identical for a socket path and a regular file;
        // use a file so this regression also runs in sandboxes that prohibit
        // creating Unix sockets.
        let listener = std::fs::File::create(&sock).unwrap();

        restrict_socket(&sock).unwrap();

        assert_eq!(mode_of(&sock), 0o600, "no other local user may connect");
        drop(listener);
        let _ = std::fs::remove_dir_all(&dir);
    }

    #[test]
    fn test_app_config_serialization() {
        let config = AppConfig {
            app_version: "external-drive-test-client@1.0.0".to_string(),
            user_agent: "test-agent/1.0".to_string(),
            cache_budget: Some(1234),
            upload_limit: Some(500_000),
            download_limit: None,
            mountpoint: Some("/tmp/x".to_string()),
            ignore_patterns: Some(vec!["build/".to_string()]),
            device_uid: Some("dev-uid".to_string()),
            conflict_sweep: Some(SweepMode::Enforce),
            open_with: None,
            prompt: None,
            proton_accent: Some(true),
            files_view: FilesView {
                list: true,
                sort: FileSort::Modified,
                descending: true,
                folders_first: false,
            },
            tray_hidden: true,
        };
        let json = serde_json::to_string(&config).unwrap();
        let decoded: AppConfig = serde_json::from_str(&json).unwrap();
        assert_eq!(decoded.app_version, "external-drive-test-client@1.0.0");
        assert_eq!(decoded.user_agent, "test-agent/1.0");
        assert_eq!(decoded.proton_accent, Some(true));
        assert!(decoded.tray_hidden);
        assert_eq!(decoded.upload_limit, Some(500_000));
        assert_eq!(decoded.download_limit, None);
        assert_eq!(decoded.files_view, config.files_view);
    }

    #[test]
    fn a_config_without_a_files_view_gets_the_default() {
        let decoded: AppConfig =
            serde_json::from_str(r#"{"app_version":"a","user_agent":"b"}"#).unwrap();
        assert_eq!(decoded.files_view, FilesView::default());
        let partial: FilesView = serde_json::from_str(r#"{"sort":"size"}"#).unwrap();
        assert_eq!(partial.sort, FileSort::Size);
        assert!(partial.folders_first);
    }

    #[test]
    fn test_default_app_config() {
        let default_config = AppConfig::default();
        assert_eq!(default_config.app_version, APP_VERSION);
        assert_eq!(default_config.user_agent, USER_AGENT);
    }

    #[test]
    fn sweep_mode_defaults_to_report_only() {
        // The sweep trashes user files, so an installed config that has never
        // heard of the setting must not get the enforcing behaviour.
        assert_eq!(SweepMode::default(), SweepMode::Report);
        assert!(!SweepMode::default().is_enforcing());
        assert_eq!(resolve_sweep_mode(None, None), SweepMode::Report);
    }

    #[test]
    fn sweep_mode_parses_operator_spellings() {
        for s in ["off", "OFF", " no ", "false", "0", "disabled"] {
            assert_eq!(SweepMode::parse(s), Some(SweepMode::Off), "{s}");
        }
        for s in ["report", "dry-run", "dryrun", "observe"] {
            assert_eq!(SweepMode::parse(s), Some(SweepMode::Report), "{s}");
        }
        for s in ["enforce", "on", "yes", "true", "1"] {
            assert_eq!(SweepMode::parse(s), Some(SweepMode::Enforce), "{s}");
        }
        // A typo must not resolve to anything, so it falls through to the config.
        assert_eq!(SweepMode::parse("offf"), None);
        assert_eq!(SweepMode::parse(""), None);
    }

    #[test]
    fn sweep_mode_env_overrides_config_but_a_typo_does_not() {
        let stored = Some(SweepMode::Enforce);
        // The point of the override: kill a destructive loop without editing config.
        assert_eq!(resolve_sweep_mode(Some("off"), stored), SweepMode::Off);
        // Unrecognised value falls back to the stored choice rather than guessing.
        assert_eq!(resolve_sweep_mode(Some("nope"), stored), SweepMode::Enforce);
        assert_eq!(resolve_sweep_mode(None, stored), SweepMode::Enforce);
        // No env, no stored value: report-only.
        assert_eq!(resolve_sweep_mode(Some("nope"), None), SweepMode::Report);
    }

    #[test]
    fn a_config_predating_conflict_sweep_still_loads() {
        let json = r#"{"app_version":"v","user_agent":"u"}"#;
        let decoded: AppConfig = serde_json::from_str(json).unwrap();
        assert!(decoded.conflict_sweep.is_none());
    }

    #[test]
    fn sweep_mode_round_trips_through_the_config_file() {
        let config = AppConfig {
            conflict_sweep: Some(SweepMode::Enforce),
            ..Default::default()
        };
        let json = serde_json::to_string(&config).unwrap();
        assert!(json.contains(r#""conflict_sweep":"enforce""#), "{json}");
        let decoded: AppConfig = serde_json::from_str(&json).unwrap();
        assert_eq!(decoded.conflict_sweep, Some(SweepMode::Enforce));
    }

    #[test]
    fn a_config_predating_ignore_patterns_still_loads() {
        // Every installed config on disk looks like this; the field must not be
        // required or the daemon would fall back to a default config on upgrade.
        let json = r#"{"app_version":"v","user_agent":"u"}"#;
        let decoded: AppConfig = serde_json::from_str(json).unwrap();
        assert!(decoded.ignore_patterns.is_none());
        assert!(!decoded.tray_hidden, "an old config keeps the tray icon");
        assert_eq!(
            decoded.resolved_ignore_patterns().len(),
            DEFAULT_IGNORE_PATTERNS.len(),
            "an absent list means the defaults apply"
        );
    }

    #[test]
    fn an_explicit_empty_ignore_list_disables_the_defaults() {
        let config = AppConfig {
            ignore_patterns: Some(Vec::new()),
            ..AppConfig::default()
        };
        assert!(
            config.resolved_ignore_patterns().is_empty(),
            "opting out must be expressible, so this cannot be unwrap_or_default"
        );
    }
}