feat: initial cosmic-gtk-config bridge

Daemon user-mode qui relie le setting CosmicTk.window_controls_position
aux fenêtres non-libcosmic :
- met à jour gtk-decoration-layout dans ~/.config/gtk-{3,4}.0/settings.ini
- aligne org.gnome.desktop.wm.preferences button-layout via gsettings
- abonné via Config::watch (cosmic-config) — propagation à chaud

Pendant : kde-gtk-config / Plasma. Limites connues : Firefox + apps
Electron qui dessinent leur propre titlebar (phase 2).

By Leyoda 2026 — MIT

.gitignore

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+/target
+Cargo.lock
+*.bak
+*.tmp

Cargo.toml

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+[package]
+name = "cosmic-gtk-config"
+version = "0.1.0"
+edition = "2021"
+license = "MIT"
+description = "Bridges the COSMIC window-controls-position setting to GTK3, GTK4 and gsettings, à la kde-gtk-config."
+authors = ["Lionel Darnis <ldarnis@gmail.com>"]
+
+[dependencies]
+cosmic-config = { path = "../libcosmic/cosmic-config", default-features = false, features = ["macro"] }
+serde = { version = "1", features = ["derive"] }
+anyhow = "1"
+log = "0.4"
+env_logger = "0.11"
+
+[profile.release]
+lto = "thin"
+codegen-units = 1
+strip = true

LICENSE

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+MIT License
+
+Copyright (c) 2026 Lionel Darnis
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

services/cosmic-gtk-config.service

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+[Unit]
+Description=COSMIC -> GTK config bridge (window controls position, theme...)
+PartOf=cosmic-session.target
+After=cosmic-session.target
+
+[Service]
+Type=simple
+ExecStart=%h/.local/bin/cosmic-gtk-config
+Restart=on-failure
+RestartSec=2
+
+[Install]
+WantedBy=cosmic-session.target

src/main.rs

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+use std::path::{Path, PathBuf};
+use std::process::Command;
+
+use anyhow::{Context, Result};
+use cosmic_config::{Config, ConfigGet};
+use serde::{Deserialize, Serialize};
+
+const COSMIC_TK_ID: &str = "com.system76.CosmicTk";
+const COSMIC_TK_VERSION: u64 = 1;
+const KEY: &str = "window_controls_position";
+
+#[derive(Debug, Clone, Copy, Default, PartialEq, Eq, Serialize, Deserialize)]
+enum WindowControlsPosition {
+    Start,
+    #[default]
+    End,
+}
+
+impl WindowControlsPosition {
+    fn gtk_layout(self) -> &'static str {
+        match self {
+            Self::Start => "close,minimize,maximize:",
+            Self::End => "menu:minimize,maximize,close",
+        }
+    }
+}
+
+fn home_path(rel: &str) -> PathBuf {
+    let home = std::env::var_os("HOME").expect("HOME unset");
+    PathBuf::from(home).join(rel)
+}
+
+fn rewrite_decoration_layout(content: &str, layout: &str) -> String {
+    let mut found = false;
+    let mut out = String::with_capacity(content.len() + 64);
+    let trailing_newline = content.ends_with('\n');
+
+    for line in content.lines() {
+        if line.starts_with("gtk-decoration-layout=") {
+            out.push_str("gtk-decoration-layout=");
+            out.push_str(layout);
+            out.push('\n');
+            found = true;
+        } else {
+            out.push_str(line);
+            out.push('\n');
+        }
+    }
+
+    if !found {
+        if !out.contains("[Settings]") {
+            out.push_str("[Settings]\n");
+        }
+        out.push_str("gtk-decoration-layout=");
+        out.push_str(layout);
+        out.push('\n');
+    }
+
+    if !trailing_newline && !out.is_empty() {
+        out.pop();
+    }
+    out
+}
+
+fn update_gtk_ini(path: &Path, layout: &str) -> Result<()> {
+    let content = if path.exists() {
+        std::fs::read_to_string(path)
+            .with_context(|| format!("read {}", path.display()))?
+    } else {
+        String::from("[Settings]\n")
+    };
+
+    let new_content = rewrite_decoration_layout(&content, layout);
+    if new_content == content {
+        log::debug!("{}: already up-to-date", path.display());
+        return Ok(());
+    }
+
+    if let Some(parent) = path.parent() {
+        std::fs::create_dir_all(parent).ok();
+    }
+
+    let tmp = path.with_extension("ini.tmp");
+    std::fs::write(&tmp, &new_content)
+        .with_context(|| format!("write {}", tmp.display()))?;
+    std::fs::rename(&tmp, path)
+        .with_context(|| format!("rename to {}", path.display()))?;
+
+    log::info!("updated {}", path.display());
+    Ok(())
+}
+
+fn update_gsettings(layout: &str) -> Result<()> {
+    let status = Command::new("gsettings")
+        .args([
+            "set",
+            "org.gnome.desktop.wm.preferences",
+            "button-layout",
+            layout,
+        ])
+        .status()
+        .context("spawn gsettings")?;
+    if !status.success() {
+        anyhow::bail!("gsettings exited with {}", status);
+    }
+    log::info!("gsettings button-layout = {}", layout);
+    Ok(())
+}
+
+fn apply(pos: WindowControlsPosition) -> Result<()> {
+    let layout = pos.gtk_layout();
+    log::info!("applying position={:?} layout={}", pos, layout);
+    update_gtk_ini(&home_path(".config/gtk-3.0/settings.ini"), layout)?;
+    update_gtk_ini(&home_path(".config/gtk-4.0/settings.ini"), layout)?;
+    update_gsettings(layout)?;
+    Ok(())
+}
+
+fn read_pos(config: &Config) -> WindowControlsPosition {
+    config
+        .get::<WindowControlsPosition>(KEY)
+        .unwrap_or_default()
+}
+
+fn main() -> Result<()> {
+    env_logger::Builder::from_env(
+        env_logger::Env::default().default_filter_or("info"),
+    )
+    .init();
+
+    let config = Config::new(COSMIC_TK_ID, COSMIC_TK_VERSION)
+        .context("open com.system76.CosmicTk config")?;
+
+    let initial = read_pos(&config);
+    log::info!("initial position: {:?}", initial);
+    apply(initial).context("initial apply failed")?;
+
+    let _watcher = config
+        .watch(|cfg, keys| {
+            if !keys.iter().any(|k| k == KEY) {
+                return;
+            }
+            let pos = cfg
+                .get::<WindowControlsPosition>(KEY)
+                .unwrap_or_default();
+            log::info!("change detected: {:?}", pos);
+            if let Err(err) = apply(pos) {
+                log::error!("apply failed: {:#}", err);
+            }
+        })
+        .context("setup watcher")?;
+
+    log::info!("daemon running, watching {}", COSMIC_TK_ID);
+    std::thread::park();
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn rewrite_replaces_existing_line() {
+        let input = "[Settings]\ngtk-theme-name=Adwaita\ngtk-decoration-layout=close,minimize,maximize:\ngtk-font-name=Sans 10\n";
+        let out = rewrite_decoration_layout(input, "menu:minimize,maximize,close");
+        assert!(out.contains("gtk-decoration-layout=menu:minimize,maximize,close\n"));
+        assert!(!out.contains("close,minimize,maximize:"));
+        assert!(out.contains("gtk-theme-name=Adwaita"));
+    }
+
+    #[test]
+    fn rewrite_appends_when_absent() {
+        let input = "[Settings]\ngtk-theme-name=Adwaita\n";
+        let out = rewrite_decoration_layout(input, "close,minimize,maximize:");
+        assert!(out.contains("gtk-decoration-layout=close,minimize,maximize:\n"));
+    }
+
+    #[test]
+    fn rewrite_creates_section_when_empty() {
+        let input = "";
+        let out = rewrite_decoration_layout(input, "close,minimize,maximize:");
+        assert!(out.contains("[Settings]"));
+        assert!(out.contains("gtk-decoration-layout=close,minimize,maximize:"));
+    }
+
+    #[test]
+    fn rewrite_preserves_no_trailing_newline() {
+        let input = "[Settings]\ngtk-decoration-layout=:minimize,maximize,close";
+        let out = rewrite_decoration_layout(input, "close,minimize,maximize:");
+        assert!(!out.ends_with('\n'));
+    }
+}