What causes "invalid appearance mode: %s" in siyuan-note/siyuan?

Pass exactly "light", "dark", or "system" (lowercase, no whitespace).

invalid appearance mode: %s

Error message

invalid appearance mode: %s

What it means

Returned by SetTheme when appearanceMode is non-empty but not one of the accepted literals "light", "dark", or "system". SetTheme switches on these three values to set ModeOS and Mode; any other string (typos, localized values, "auto", "Light") falls through to the default branch and is rejected.

Source

Thrown at kernel/model/appearance.go:114

					return fmt.Errorf("theme [%s] not exists or not available for dark mode", theme)
				}
				Conf.Appearance.ThemeDark = theme
			}
		}
	}

	if appearanceMode != "" {
		switch appearanceMode {
		case "light":
			Conf.Appearance.ModeOS = false
			Conf.Appearance.Mode = 0
		case "dark":
			Conf.Appearance.ModeOS = false
			Conf.Appearance.Mode = 1
		case "system":
			Conf.Appearance.ModeOS = true
		default:
			return fmt.Errorf("invalid appearance mode: %s", appearanceMode)
		}
	}
	return nil
}

func containTheme(name string, themes []*conf.AppearanceTheme) bool {
	for _, t := range themes {
		if t.Name == name {
			return true
		}
	}
	return false
}

func containIcon(name string, icons []*conf.AppearanceIcon) bool {
	for _, i := range icons {
		if i.Name == name {
			return true

View on GitHub (pinned to 251596fc0d)

Solutions

Pass exactly "light", "dark", or "system" (lowercase, no whitespace).
Trim and lowercase the value before calling SetTheme if it originates from user input.
Pass an empty string to leave the appearance mode unchanged.

Example fix

// before
model.SetTheme("daylight", []int{0}, "Light ")
// after
mode := strings.ToLower(strings.TrimSpace("Light "))
model.SetTheme("daylight", []int{0}, mode)  // "light"

Defensive patterns

Strategy: validation

Validate before calling

switch strings.ToLower(strings.TrimSpace(appearanceMode)) {
case "", "light", "dark", "system":
default:
    return fmt.Errorf("invalid appearance mode: %s", appearanceMode)
}

Type guard

func validAppearanceMode(mode string) bool {
    switch mode {
    case "", "light", "dark", "system": return true
    }
    return false
}

Prevention

Normalize mode input: trim whitespace and lowercase before calling SetTheme.
Pass an empty string to leave the mode unchanged.
Use the canonical literals light/dark/system; avoid localized or capitalized variants.

When it happens

Trigger: Calling SetTheme with an appearanceMode such as "auto", "Light", "day", or any non-English/localized word; passing an uppercase variant; trailing whitespace in the value.

Common situations: A client sends a localized or capitalized mode string; a typo; whitespace from user input not trimmed; confusion with theme-mode integers (passing "0"/"1" instead of "light"/"dark").

Related errors

AI-assisted analysis of siyuan-note/siyuan@251596fc0d (2026-08-12). Data as JSON: /api/errors/2bad57dca05c7ede. Report an issue: GitHub.