Module theme 

Cross-platform OS appearance (dark/light) detection.

We hand-roll this so we don’t depend on dark-light, which in v2.x pulls in the now-unmaintained async-std (RUSTSEC-2025-0052).

Per AGENTS.md §4: dark + light mode follow MUST work on Windows, macOS, and Linux without third-party crates beyond the standard ecosystem. The Python reference implementation (the previous generation of this tool) demonstrated that the algorithm fits in about thirty lines per platform; this is the Rust translation.

Precedence:

1. NO_COLOR -> Appearance::Unknown (let caller decide).
2. COLORFGBG -> parsed foreground;background colours.
3. Per-OS native probe -> Windows registry / macOS defaults / GNOME gsettings / KDE kdeglobals.
4. Fallback -> Appearance::Unknown.

Enums

Appearance

ThemeChoice

User-visible theme preference, stored in the config file as a string ("auto", "dark", "light"). A string is used on disk so older configs (and hand-edited files with typos) keep loading; unknown values silently fall back to ThemeChoice::Auto.

Functions

detect

Best-effort current OS appearance.