What causes "Unknown theme preset: {unknown}" in gitbutlerapp/gitbutler?

Use 'dark' or 'light' (case-insensitive)

gitbutlerapp/gitbutler · error · anyhow::Error

Unknown theme preset: {unknown}

Error message

Unknown theme preset: {unknown}

What it means

ThemePreset::from_str normalizes case and surrounding whitespace but accepts only the exact values 'dark' and 'light'. Any other string supplied via theme config or a CLI flag fails this parse error.

Source

Thrown at crates/but/src/theme.rs:234

/// Identifiers for the theme presets.
#[derive(Debug, PartialEq, Eq, Clone)]
pub enum ThemePreset {
    /// The dark preset.
    Dark,
    /// The light preset.
    Light,
}

impl FromStr for ThemePreset {
    type Err = anyhow::Error;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        let normalized = s.to_lowercase();
        match normalized.trim() {
            "dark" => Ok(ThemePreset::Dark),
            "light" => Ok(ThemePreset::Light),
            unknown => Err(anyhow::anyhow!("Unknown theme preset: {unknown}")),
        }
    }
}

/// Detect the theme preset from the terminal's foreground and background colors.
///
/// Returns `None` if the terminal does not support color queries or does not respond in time.
pub(crate) fn detect_terminal_preset() -> Option<ThemePreset> {
    terminal_colorsaurus::theme_mode(terminal_colorsaurus::QueryOptions::default())
        .ok()
        .map(theme_preset_from_terminal_mode)
}

fn theme_preset_from_terminal_mode(mode: terminal_colorsaurus::ThemeMode) -> ThemePreset {
    match mode {
        terminal_colorsaurus::ThemeMode::Dark => ThemePreset::Dark,
        terminal_colorsaurus::ThemeMode::Light => ThemePreset::Light,
    }

View on GitHub (pinned to caf1f223d3)

Solutions

Use 'dark' or 'light' (case-insensitive)
Omit the setting so but falls back to detecting the terminal theme (detect_terminal_preset)
Check the config file for typos, quotes, or trailing whitespace around the value

Example fix

# before
theme = "auto"   # not a valid preset
# after
theme = "dark"   # or "light", or remove the key for auto-detection

Defensive patterns

Strategy: validation

Validate before calling

fn is_theme_preset(s: &str) -> bool {
    matches!(s.trim().to_lowercase().as_str(), "dark" | "light")
}

Type guard

fn theme_preset_or_none(s: &str) -> Option<ThemePreset> {
    match s.trim().to_lowercase().as_str() {
        "dark" => Some(ThemePreset::Dark),
        "light" => Some(ThemePreset::Light),
        _ => None,
    }
}

Prevention

Validate theme values against the enum before writing config
Fall back to detect_terminal_preset() on unknown values instead of failing

When it happens

Trigger: Setting the theme preset to anything other than dark/light, such as 'auto', 'system', 'terminal', or 'high-contrast', in the config file or on the command line.

Common situations: Users expecting 'auto'/'system' to trigger terminal color detection; configs copied from other tools with different vocabulary; stray whitespace or quotes around the value.

Understand the failure class

Background: "Invalid value" and "allowed values are" config errors: what your library rejected and how to fix it — this error's family across 41 libraries.

Related errors

AI-assisted analysis of gitbutlerapp/gitbutler@caf1f223d3 (2026-08-20). Data as JSON: /api/errors/16fa1ce0d02c0a0a. Report an issue: GitHub.