Ignore locale if unsupported by X11 backend (#1445)

This restores default portable 'C' locale when target locale is unsupported
by X11 backend (Xlib).

When target locale is unsupported by X11, some locale-dependent Xlib
functions like `XSetLocaleModifiers` fail or have no effect triggering
later failures and panics.

When target locale is not valid, `setLocale` should normally leave the
locale unchanged (`setLocale` returns 'C'). However, in some situations,
locale is accepted by `setLocale` (`setLocale` returns the new locale)
but the accepted locale is unsupported by Xlib (`XSupportsLocale` returns
`false`).

Fix #636

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 - On Wayland, fix coordinates in touch events when scale factor isn't 1.
 - On Wayland, fix color from `close_button_icon_color` not applying.
+- Ignore locale if unsupported by X11 backend
 
 # 0.21.0 (2020-02-04)
 

src/platform_impl/linux/x11/ime/input_method.rs

@@ -21,7 +21,8 @@ unsafe fn open_im(xconn: &Arc<XConnection>, locale_modifiers: &CStr) -> Option<f
     // XSetLocaleModifiers returns...
     // * The current locale modifiers if it's given a NULL pointer.
     // * The new locale modifiers if we succeeded in setting them.
-    // * NULL if the locale modifiers string is malformed.
+    // * NULL if the locale modifiers string is malformed or if the
+    //   current locale is not supported by Xlib.
     (xconn.xlib.XSetLocaleModifiers)(locale_modifiers.as_ptr());
 
     let im = (xconn.xlib.XOpenIM)(

src/platform_impl/linux/x11/mod.rs

@@ -29,6 +29,7 @@ use std::{
     mem::{self, MaybeUninit},
     ops::Deref,
     os::raw::*,
+    ptr,
     rc::Rc,
     slice,
     sync::{mpsc, Arc, Mutex, Weak},
@@ -105,7 +106,25 @@ impl<T: 'static> EventLoop<T> {
         // Input methods will open successfully without setting the locale, but it won't be
         // possible to actually commit pre-edit sequences.
         unsafe {
+            // Remember default locale to restore it if target locale is unsupported
+            // by Xlib
+            let default_locale = setlocale(LC_CTYPE, ptr::null());
             setlocale(LC_CTYPE, b"\0".as_ptr() as *const _);
+
+            // Check if set locale is supported by Xlib.
+            // If not, calls to some Xlib functions like `XSetLocaleModifiers`
+            // will fail.
+            let locale_supported = (xconn.xlib.XSupportsLocale)() == 1;
+            if !locale_supported {
+                let unsupported_locale = setlocale(LC_CTYPE, ptr::null());
+                warn!(
+                    "Unsupported locale \"{}\". Restoring default locale \"{}\".",
+                    CStr::from_ptr(unsupported_locale).to_string_lossy(),
+                    CStr::from_ptr(default_locale).to_string_lossy()
+                );
+                // Restore default locale
+                setlocale(LC_CTYPE, default_locale);
+            }
         }
         let ime = RefCell::new({
             let result = Ime::new(Arc::clone(&xconn));