meh2

meh with a Rhai engine, a plugin system, and Python-free polling.

meh2 is a GTK4 Wayland widget system and status bar — a fork of meh that adds in-process Rhai scripting, a Rhai plugin system, and inotify-backed file subscriptions. Your existing yuck/meh configs work without modification; Rhai is purely additive.

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Features

• Yuck configuration — same S-expression language as eww/meh. Existing configs are compatible.
• GTK4 + Wayland-native — gtk4-layer-shell, fractional scaling, hardware-accelerated rendering. No X11.
• Rhai scripting engine — .rhai files and rhai: inline expressions as defpoll/deflisten sources. Runs in-process, no fork; AST compiled once and cached (< 1 ms per tick).
• Rhai plugin system — drop a directory into ~/.config/meh2/plugins/; plugins contribute vars and custom defwidgets declared in plugin.toml.
• Rhai widgets — (rhai-widget) builds live widget trees from a Rhai function, rebuilt only when its watched vars change.
• Python-free polling — json_decode, string ops, and run_shell cover every use case; no Python interpreter in the poll path.
• Reactive bindings — variable updates push only to affected widgets. No full tree rebuilds.
• Granular hot reload — meh2 reload rebuilds only windows whose definition changed; unchanged windows keep their state.
• Poll gating — defpoll and deflisten subprocesses pause when no windows are open. Idle daemon sits at ~0.17% CPU.
• defsubscribe — inotify file watchers (with tilde expansion + atomic-write support) and DBus property watchers. Zero-cost reactive sources — no polling, no subprocess.
• Deflisten process groups — deflisten subprocesses run while windows are open (gated like defpoll when the bar is hidden); SIGTERM on shutdown reaches grandchildren (inotifywait, playerctl --follow, nmcli monitor, etc.).
• Declarative animations — AdwTimedAnimation on progress values and opacity. Interruptible, respects system reduced-motion.
• Native app launcher — (launcher) widget: instant gio::AppInfo search, PATH executable autocomplete, keyboard nav, click-to-launch.
• System tray — StatusNotifierItem/StatusNotifierHost. Opt-in: cargo build --features systray or --features full.
• (shader) widget — GLSL fragment shaders via GtkGLArea. Full profile only.
• Heap trimming — popups are destroyed with gtk_window_destroy() and malloc_trim(0) returns freed image memory to the OS, keeping resident memory flat over long uptimes.
• Plugin sandbox — plugin.toml permissions enforce file read allowlists and opt-in run_shell().
• Versioned IPC — CLI/daemon protocol v1; mismatched versions fail with a clear error.
• Three build profiles: minimal, default (rhai + dbus + animations — no systray/plugins), full (+ systray, plugins, shader).

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Performance

Metric	meh	meh2
Idle CPU (static bar)	~0.17%	~0.17%
Idle CPU (1s clock)	~0.35%	~0.35%
Poll latency (shell)	~1.3–1.8 ms	~1.3–1.8 ms
Poll latency (Rhai)	N/A	< 1 ms (no fork)
Python in poll path	Required	None
Persistent subprocess RSS	~5–6 MB each	None when using Rhai
Rhai engine overhead	N/A	~2–4 MB RSS
Resident memory (bar, cairo renderer)	—	~28 MB, flat
Poll gating	Windows-closed pause	defpoll + deflisten pause
Listen subprocess RSS	~5–6 MB each (always on)	Gated when bar hidden
Plugin permissions	N/A	Enforced sandbox in plugin.toml

Memory. Popups are torn down with gtk_window_destroy() (not close(), which only hides them and leaks the widget tree), and a malloc_trim(0) after each popup closes returns the freed image memory to the OS — so resident memory stays flat no matter how many menus you open. Run the bar with the cairo GSK renderer (GSK_RENDERER=cairo) for the lowest footprint (~28 MB); the default Vulkan renderer holds ~50 MB of GPU buffers for otherwise-static bar content.

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What meh2 adds over meh

Feature	meh	meh2
Poll sources	Shell scripts only	.rhai files + rhai: inline + shell
Event handlers	Shell commands	.rhai files + rhai: inline + shell
Plugin system	None	Rhai plugins in ~/.config/meh2/plugins/ (sandboxed)
Widget builders	defwidget in yuck only	(rhai-widget) + plugin-registered widgets
File watching	defsubscribe :inotify	defsubscribe :file with tilde expansion + atomic-write support
Python in poll path	Required for complex scripts	Zero — json_decode, string ops, run_shell cover every use case
Poll latency (Rhai)	N/A	< 1 ms (no fork, AST cached)
Poll latency (shell)	~1.3–1.8 ms	Same — shell path unchanged

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Rhai API

Scripts have access to a sandboxed API. Config scripts (defpoll, event handlers, user (rhai-widget)) are unrestricted. Plugin scripts are limited by [permissions] in plugin.toml (see docs/plugins.md).

read_file(path)          → string    silent "" on NotFound
read_or(path, default)   → string    returns default if missing/empty
write_cache(key, value)  → bool      writes to ~/.cache/meh2/<key>
read_cache(key)          → string    reads from ~/.cache/meh2/<key>
run_shell(cmd)           → string    stdout of sh -c cmd (logged)
parse_int(s)             → i64
parse_float(s)           → f64
env_var(name)            → string
path_exists(path)        → bool
json_decode(json_str)    → Dynamic   JSON object/array/value → Rhai
json_encode(value)       → string    any Rhai value → JSON string

Gotchas

• string.trim() and string.replace() are in-place — they return (), not the new value.
• Template strings `${var}` work in .rhai files but not inside yuck strings (use + instead).
• No built-in regex — use split(), contains(), index_of(), sub_string().

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Installation

Arch Linux

git clone https://github.com/sickhate/meh2
cd meh2
makepkg -si

From source

git clone https://github.com/sickhate/meh2
cd meh2
cargo build --release
sudo install -Dm755 target/release/meh2 /usr/bin/meh2

Runtime dependencies: gtk4, gtk4-layer-shell, libadwaita, cairo, glib2, pango

Build dependencies: rust (stable), cargo

Build profiles

# Minimal — no Rhai, no tray, no animations
cargo build --release --no-default-features --features minimal

# Default — Rhai, dbus, inotify, animations (no systray or plugins)
cargo build --release

# Full — default + systray + Rhai plugins + GLSL shaders
cargo build --release --features full

# À la carte — e.g. systray only
cargo build --release --features systray

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Quick start

meh2 daemon
meh2 open bar
meh2 reload   # hot reload — only changed windows restart
meh2 close bar
meh2 update MY_VAR=hello

Config lives in ~/.config/meh2/. Main file: meh2.yuck (or eww.yuck). CSS: style.scss.

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Example — Rhai poll source

(defpoll CPU :interval "2s" "scripts/getCpu.rhai")

(defwidget cpu-bar []
  (label :text "${CPU.pct}% ${CPU.temp}°C"))

// scripts/getCpu.rhai
let stat = read_file("/proc/stat");
let nums = [];
for p in stat.split("\n")[0].split(" ") {
    if p != "" && p != "cpu" { nums += p; }
}
let idle  = parse_int(nums[3]);
let total = parse_int(nums[0]) + parse_int(nums[1]) + parse_int(nums[2]) + idle + parse_int(nums[4]);

let prev = read_cache("cpu_prev").split(",");
let pct  = 0;
if prev.len() >= 2 {
    let dt = total - parse_int(prev[0]);
    let di = idle  - parse_int(prev[1]);
    if dt > 0 { pct = ((dt - di) * 100) / dt; }
}
write_cache("cpu_prev", total + "," + idle);

let temp = parse_int(read_file("/sys/class/thermal/thermal_zone0/temp")) / 1000;
`{"pct":${pct},"temp":${temp}}`

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Example — defsubscribe :file

; Instant inotify response — no polling, zero overhead when file doesn't change
(defsubscribe THEME :file "~/.local/share/meh2/theme" :initial "dark")

The watcher handles missing files (watches parent dir), atomic writes (rm+recreate), and tilde paths.

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Example — Rhai plugin

~/.config/meh2/plugins/sysinfo/
├── plugin.toml
└── main.rhai

# plugin.toml
name    = "sysinfo"
version = "0.1.0"

[permissions]
read_files  = ["/proc/stat", "/proc/meminfo"]
allow_shell = false

[[vars]]
name     = "PLUGIN_CPU"
interval = "3s"

[[widgets]]
name          = "sysinfo-pill"
fn_name       = "render_sysinfo_pill"
default_watch = ["PLUGIN_CPU"]

// main.rhai
fn get_PLUGIN_CPU() {
    let pct = parse_int(read_file("/sys/class/thermal/thermal_zone0/temp")) / 1000;
    `{"pct":${pct}}`
}

fn render_sysinfo_pill() #{
    type: "label",
    text: "CPU " + PLUGIN_CPU.pct + "%"
}

Use in yuck: (sysinfo-pill) — no :src or :fn needed.

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Project layout

crates/
├── cli/           meh2 binary
├── daemon/        lifecycle + IPC server
├── core/          config, paths, IPC protocol (v1)
├── gtk4-impl/     GTK widgets — bindings.rs, builder.rs, widgets.rs, runtime.rs
├── script-vars/   defpoll / deflisten / defsubscribe
├── rhai-engine/   Rhai runtime + plugin sandbox
├── plugin-host/   plugin discovery + poll tasks
├── notifier-host/ system tray (systray feature)
├── yuck/          config language (MIT/eww)
└── simplexpr/     expression evaluator (MIT/eww)
docs/plugins.md    plugin authoring + permissions

Run tests: cargo test --release --locked

Arch package build artifacts (pkg/, *.pkg.tar.zst) are gitignored.

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Phase status

Phase	Description	Status
0	Fork baseline — meh2 binary, config dir, socket prefix	Complete
1	Rhai poll/listen sources	Complete
2	Rhai event handlers	Complete
3	Rhai plugin system	Complete
4	(rhai-widget) — Rhai-defined widget trees	Complete
4.5	Plugin-registered defwidgets	Complete
5	Hybrid yuck+Rhai (inline Rhai in attr expressions)	Planned

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Acknowledgements

• meh — the direct parent project this forks from
• elkowar/eww — the original yuck language and concept. MIT licensed.
• Ewwii-sh/ewwii — completed the GTK4 port. GPL-3.0.

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License

GPL-3.0-or-later. See LICENSE.

Code copied or adapted from elkowar/eww retains its MIT header.