env: Pass through locale & IM stuff

Leaving the default C locale can break stuff that expect UTF-8, so pass
through all the locale env vars and set a default C.UTF-8 locale if
nothing is set.

For input methods, it turns out that the old legacy XIM does work with
our X11 passthrough solution (direct GTK/QT plugin methods will not,
since they use side-channels to communicate with the IM server). So,
force xim usage for GTK2/3 and QT4/5, which actually works with Steam
(!) for CJK input if the system is configured properly.

The future is Wayland protocols, which will work with GTK4 and QT6 once
we have Wayland passthrough. Hopefully that means we never have to
support input methods with the shared library mechanisms, which means
our rootfs will never have to include IM-specific libraries and the
input method user choice will happen entirely outside of muvm.

Signed-off-by: Asahi Lina <[email protected]>

crates/muvm/src/env.rs

@@ -10,12 +10,27 @@ use log::debug;
 
 /// Automatically pass these environment variables to the microVM, if they are
 /// set.
-const WELL_KNOWN_ENV_VARS: [&str; 5] = [
+const WELL_KNOWN_ENV_VARS: [&str; 20] = [
+    "LANG",
+    "LC_ADDRESS",
+    "LC_ALL",
+    "LC_COLLATE",
+    "LC_CTYPE",
+    "LC_IDENTIFICATION",
+    "LC_MEASUREMENT",
+    "LC_MESSAGES",
+    "LC_MONETARY",
+    "LC_NAME",
+    "LC_NUMERIC",
+    "LC_PAPER",
+    "LC_TELEPHONE",
+    "LC_TIME",
     "LD_LIBRARY_PATH",
     "LIBGL_DRIVERS_PATH",
     "MESA_LOADER_DRIVER_OVERRIDE", // needed for asahi
     "PATH",                        // needed by `muvm-guest` program
     "RUST_LOG",
+    "XMODIFIERS",
 ];
 
 /// See https://github.com/AsahiLinux/docs/wiki/Devices
@@ -56,6 +71,23 @@ pub fn prepare_env_vars(env: Vec<(String, Option<String>)>) -> Result<HashMap<St
         env_map.insert(key.to_owned(), value);
     }
 
+    if !(env_map.contains_key("LANG")
+        || env_map.contains_key("LC_CTYPE")
+        || env_map.contains_key("LC_ALL"))
+    {
+        // Set a default UTF-8 locale if none
+        env_map.insert("LANG".to_owned(), "C.UTF-8".to_owned());
+    }
+
+    // Force XIM usage for GTK2/3 and QT4/QT5 (QT6 and GTK4 drop this).
+    // This actually works with muvm-x11bridge for input methods in Steam,
+    // since it ships the xim plugin for its bundled gtk3.
+    // Once we have wayland, the Wayland transport should work for newer stuff.
+    // This way we don't need to support passing through the dbus/socket based
+    // direct plugin support.
+    env_map.insert("GTK_IM_MODULE".to_owned(), "xim".to_owned());
+    env_map.insert("QT_IM_MODULE".to_owned(), "xim".to_owned());
+
     for (key, value) in env {
         let value = value.map_or_else(
             || env::var(&key).with_context(|| format!("Failed to get `{key}` env var")),