x11: Overhaul XIM code (#451)

Fixes #195
Fixes #277
Fixes #455

* Read `XMODIFIERS` explicitly/directly instead of calling `XSetLocaleModifiers` with an
empty string. This is useful for debugging purposes, and more clear to read and handle.
* Fallback to local input method if the one specified in `XMODIFIERS` is later closed on the
server end (i.e. if ibus/fcitx is terminated). Previously, that would cause the event loop
to freeze and usually also segfault.
* If using the fallback input method, respond to the `XMODIFIERS` input method later
becoming available. This means that the input method restarting is handled, and that even if
the program was started while ibus/fcitx/etc. was unavailable, it will start using it as
soon as it becomes available.
* Only one input method is opened for the whole event loop, with each window having its own
input context.
* IME works completely out of the box now, no longer requiring application developers to
call `setlocale` or `XSetLocaleModifiers`.
* Detailed error messages are provided if no input method could be opened. However, no
information is provided to the user if their intended `XMODIFIERS` input method failed to
open but the fallbacks (which will ostensibly always succeed) succeeded; in my opinion, this
is something that is best filled by adding a logging feature to winit.

CHANGELOG.md

@@ -3,6 +3,7 @@
 - Overhauled X11 window geometry calculations. `get_position` and `set_position` are more universally accurate across different window managers, and `get_outer_size` actually works now.
 - Fixed SIGSEGV/SIGILL crashes on macOS caused by stabilization of the `!` (never) type.
 - Implement `WindowEvent::HiDPIFactorChanged` for macOS
+- On X11, input methods now work completely out of the box, no longer requiring application developers to manually call `setlocale`. Additionally, when input methods are started, stopped, or restarted on the server end, it's correctly handled.
 
 # Version 0.12.0 (2018-04-06)
 

src/platform/linux/x11/ime/callbacks.rs

@@ -0,0 +1,185 @@
+use std::ptr;
+use std::sync::Arc;
+use std::collections::HashMap;
+use std::os::raw::c_char;
+
+use super::{ffi, XConnection, XError};
+
+use super::inner::{close_im, ImeInner};
+use super::input_method::PotentialInputMethods;
+use super::context::{ImeContextCreationError, ImeContext};
+
+pub unsafe fn xim_set_callback(
+    xconn: &Arc<XConnection>,
+    xim: ffi::XIM,
+    field: *const c_char,
+    callback: *mut ffi::XIMCallback,
+) -> Result<(), XError> {
+    // It's advisable to wrap variadic FFI functions in our own functions, as we want to minimize
+    // access that isn't type-checked.
+    (xconn.xlib.XSetIMValues)(
+        xim,
+        field,
+        callback,
+        ptr::null_mut::<()>(),
+    );
+    xconn.check_errors()
+}
+
+// Set a callback for when an input method matching the current locale modifiers becomes
+// available. Note that this has nothing to do with what input methods are open or able to be
+// opened, and simply uses the modifiers that are set when the callback is set.
+// * This is called per locale modifier, not per input method opened with that locale modifier.
+// * Trying to set this for multiple locale modifiers causes problems, i.e. one of the rebuilt
+//   input contexts would always silently fail to use the input method.
+pub unsafe fn set_instantiate_callback(
+    xconn: &Arc<XConnection>,
+    client_data: ffi::XPointer,
+) -> Result<(), XError> {
+    (xconn.xlib.XRegisterIMInstantiateCallback)(
+        xconn.display,
+        ptr::null_mut(),
+        ptr::null_mut(),
+        ptr::null_mut(),
+        Some(xim_instantiate_callback),
+        client_data,
+    );
+    xconn.check_errors()
+}
+
+pub unsafe fn unset_instantiate_callback(
+    xconn: &Arc<XConnection>,
+    client_data: ffi::XPointer,
+) -> Result<(), XError> {
+    (xconn.xlib.XUnregisterIMInstantiateCallback)(
+        xconn.display,
+        ptr::null_mut(),
+        ptr::null_mut(),
+        ptr::null_mut(),
+        Some(xim_instantiate_callback),
+        client_data,
+    );
+    xconn.check_errors()
+}
+
+pub unsafe fn set_destroy_callback(
+    xconn: &Arc<XConnection>,
+    im: ffi::XIM,
+    inner: &ImeInner,
+) -> Result<(), XError> {
+    xim_set_callback(
+        &xconn,
+        im,
+        ffi::XNDestroyCallback_0.as_ptr() as *const _,
+        &inner.destroy_callback as *const _ as *mut _,
+    )
+}
+
+#[derive(Debug)]
+enum ReplaceImError {
+    MethodOpenFailed(PotentialInputMethods),
+    ContextCreationFailed(ImeContextCreationError),
+    SetDestroyCallbackFailed(XError),
+}
+
+// Attempt to replace current IM (which may or may not be presently valid) with a new one. This
+// includes replacing all existing input contexts and free'ing resources as necessary. This only
+// modifies existing state if all operations succeed.
+unsafe fn replace_im(inner: *mut ImeInner) -> Result<(), ReplaceImError> {
+    let xconn = &(*inner).xconn;
+
+    let (new_im, is_fallback) = {
+        let new_im = (*inner).potential_input_methods.open_im(xconn, None);
+        let is_fallback = new_im.is_fallback();
+        (
+            new_im.ok().ok_or_else(|| {
+                ReplaceImError::MethodOpenFailed((*inner).potential_input_methods.clone())
+            })?,
+            is_fallback,
+        )
+    };
+
+    // It's important to always set a destroy callback, since there's otherwise potential for us
+    // to try to use or free a resource that's already been destroyed on the server.
+    {
+        let result = set_destroy_callback(xconn, new_im.im, &*inner);
+        if result.is_err() {
+            let _ = close_im(xconn, new_im.im);
+        }
+        result
+    }.map_err(ReplaceImError::SetDestroyCallbackFailed)?;
+
+    let mut new_contexts = HashMap::new();
+    for (window, old_context) in (*inner).contexts.iter() {
+        let spot = old_context.as_ref().map(|old_context| old_context.ic_spot);
+        let new_context = {
+            let result = ImeContext::new(
+                xconn,
+                new_im.im,
+                *window,
+                spot,
+            );
+            if result.is_err() {
+                let _ = close_im(xconn, new_im.im);
+            }
+            result.map_err(ReplaceImError::ContextCreationFailed)?
+        };
+        new_contexts.insert(*window, Some(new_context));
+    }
+
+    // If we've made it this far, everything succeeded.
+    let _ = (*inner).destroy_all_contexts_if_necessary();
+    let _ = (*inner).close_im_if_necessary();
+    (*inner).im = new_im.im;
+    (*inner).contexts = new_contexts;
+    (*inner).is_destroyed = false;
+    (*inner).is_fallback = is_fallback;
+    Ok(())
+}
+
+pub unsafe extern fn xim_instantiate_callback(
+    _display: *mut ffi::Display,
+    client_data: ffi::XPointer,
+    // This field is unsupplied.
+    _call_data: ffi::XPointer,
+) {
+    let inner: *mut ImeInner = client_data as _;
+    if !inner.is_null() {
+        let xconn = &(*inner).xconn;
+        let result = replace_im(inner);
+        if result.is_ok() {
+            let _ = unset_instantiate_callback(xconn, client_data);
+            (*inner).is_fallback = false;
+        } else if result.is_err() && (*inner).is_destroyed {
+            // We have no usable input methods!
+            result.expect("Failed to reopen input method");
+        }
+    }
+}
+
+// This callback is triggered when the input method is closed on the server end. When this
+// happens, XCloseIM/XDestroyIC doesn't need to be called, as the resources have already been
+// free'd (attempting to do so causes our connection to freeze).
+pub unsafe extern fn xim_destroy_callback(
+    _xim: ffi::XIM,
+    client_data: ffi::XPointer,
+    // This field is unsupplied.
+    _call_data: ffi::XPointer,
+) {
+    let inner: *mut ImeInner = client_data as _;
+    if !inner.is_null() {
+        (*inner).is_destroyed = true;
+        let xconn = &(*inner).xconn;
+        if !(*inner).is_fallback {
+            let _ = set_instantiate_callback(xconn, client_data);
+            // Attempt to open fallback input method.
+            let result = replace_im(inner);
+            if result.is_ok() {
+                (*inner).is_fallback = true;
+            } else {
+                // We have no usable input methods!
+                result.expect("Failed to open fallback input method");
+            }
+        }
+    }
+}

src/platform/linux/x11/ime/context.rs

@@ -0,0 +1,134 @@
+use std::ptr;
+use std::sync::Arc;
+use std::os::raw::{c_short, c_void};
+
+use super::{ffi, util, XConnection, XError};
+
+#[derive(Debug)]
+pub enum ImeContextCreationError {
+    XError(XError),
+    Null,
+}
+
+unsafe fn create_pre_edit_attr<'a>(
+    xconn: &'a Arc<XConnection>,
+    ic_spot: &'a ffi::XPoint,
+) -> util::XSmartPointer<'a, c_void> {
+    util::XSmartPointer::new(
+        xconn,
+        (xconn.xlib.XVaCreateNestedList)(
+            0,
+            ffi::XNSpotLocation_0.as_ptr() as *const _,
+            ic_spot,
+            ptr::null_mut::<()>(),
+        ),
+    ).expect("XVaCreateNestedList returned NULL")
+}
+
+// WARNING: this struct doesn't destroy its XIC resource when dropped.
+// This is intentional, as it doesn't have enough information to know whether or not the context
+// still exists on the server. Since `ImeInner` has that awareness, destruction must be handled
+// through `ImeInner`.
+#[derive(Debug)]
+pub struct ImeContext {
+    pub ic: ffi::XIC,
+    pub ic_spot: ffi::XPoint,
+}
+
+impl ImeContext {
+    pub unsafe fn new(
+        xconn: &Arc<XConnection>,
+        im: ffi::XIM,
+        window: ffi::Window,
+        ic_spot: Option<ffi::XPoint>,
+    ) -> Result<Self, ImeContextCreationError> {
+        let ic = if let Some(ic_spot) = ic_spot {
+            ImeContext::create_ic_with_spot(xconn, im, window, ic_spot)
+        } else {
+            ImeContext::create_ic(xconn, im, window)
+        };
+
+        let ic = ic.ok_or(ImeContextCreationError::Null)?;
+        xconn.check_errors().map_err(ImeContextCreationError::XError)?;
+
+        Ok(ImeContext {
+            ic,
+            ic_spot: ic_spot.unwrap_or_else(|| ffi::XPoint { x: 0, y: 0 }),
+        })
+    }
+
+    unsafe fn create_ic(
+        xconn: &Arc<XConnection>,
+        im: ffi::XIM,
+        window: ffi::Window,
+    ) -> Option<ffi::XIC> {
+        let ic = (xconn.xlib.XCreateIC)(
+            im,
+            ffi::XNInputStyle_0.as_ptr() as *const _,
+            ffi::XIMPreeditNothing | ffi::XIMStatusNothing,
+            ffi::XNClientWindow_0.as_ptr() as *const _,
+            window,
+            ptr::null_mut::<()>(),
+        );
+        if ic.is_null() {
+            None
+        } else {
+            Some(ic)
+        }
+    }
+
+    unsafe fn create_ic_with_spot(
+        xconn: &Arc<XConnection>,
+        im: ffi::XIM,
+        window: ffi::Window,
+        ic_spot: ffi::XPoint,
+    ) -> Option<ffi::XIC> {
+        let pre_edit_attr = create_pre_edit_attr(xconn, &ic_spot);
+        let ic = (xconn.xlib.XCreateIC)(
+            im,
+            ffi::XNInputStyle_0.as_ptr() as *const _,
+            ffi::XIMPreeditNothing | ffi::XIMStatusNothing,
+            ffi::XNClientWindow_0.as_ptr() as *const _,
+            window,
+            ffi::XNPreeditAttributes_0.as_ptr() as *const _,
+            pre_edit_attr.ptr,
+            ptr::null_mut::<()>(),
+        );
+        if ic.is_null() {
+            None
+        } else {
+            Some(ic)
+        }
+    }
+
+    pub fn focus(&self, xconn: &Arc<XConnection>) -> Result<(), XError> {
+        unsafe {
+            (xconn.xlib.XSetICFocus)(self.ic);
+        }
+        xconn.check_errors()
+    }
+
+    pub fn unfocus(&self, xconn: &Arc<XConnection>) -> Result<(), XError> {
+        unsafe {
+            (xconn.xlib.XUnsetICFocus)(self.ic);
+        }
+        xconn.check_errors()
+    }
+
+    pub fn set_spot(&mut self, xconn: &Arc<XConnection>, x: c_short, y: c_short) {
+        if self.ic_spot.x == x && self.ic_spot.y == y {
+            return;
+        }
+        self.ic_spot = ffi::XPoint { x, y };
+
+        unsafe {
+            let pre_edit_attr = create_pre_edit_attr(xconn, &self.ic_spot);
+            (xconn.xlib.XSetICValues)(
+                self.ic,
+                ffi::XNPreeditAttributes_0.as_ptr() as *const _,
+                pre_edit_attr.ptr,
+                ptr::null_mut::<()>(),
+            );
+        }
+    }
+}

src/platform/linux/x11/ime/inner.rs

@@ -0,0 +1,75 @@
+use std::mem;
+use std::ptr;
+use std::sync::Arc;
+use std::collections::HashMap;
+
+use super::{ffi, XConnection, XError};
+
+use super::input_method::PotentialInputMethods;
+use super::context::ImeContext;
+
+pub unsafe fn close_im(xconn: &Arc<XConnection>, im: ffi::XIM) -> Result<(), XError> {
+    (xconn.xlib.XCloseIM)(im);
+    xconn.check_errors()
+}
+
+pub unsafe fn destroy_ic(xconn: &Arc<XConnection>, ic: ffi::XIC) -> Result<(), XError> {
+    (xconn.xlib.XDestroyIC)(ic);
+    xconn.check_errors()
+}
+
+pub struct ImeInner {
+    pub xconn: Arc<XConnection>,
+    // WARNING: this is initially null!
+    pub im: ffi::XIM,
+    pub potential_input_methods: PotentialInputMethods,
+    pub contexts: HashMap<ffi::Window, Option<ImeContext>>,
+    // WARNING: this is initially zeroed!
+    pub destroy_callback: ffi::XIMCallback,
+    // Indicates whether or not the the input method was destroyed on the server end
+    // (i.e. if ibus/fcitx/etc. was terminated/restarted)
+    pub is_destroyed: bool,
+    pub is_fallback: bool,
+}
+
+impl ImeInner {
+    pub fn new(
+        xconn: Arc<XConnection>,
+        potential_input_methods: PotentialInputMethods,
+    ) -> Self {
+        ImeInner {
+            xconn,
+            im: ptr::null_mut(),
+            potential_input_methods,
+            contexts: HashMap::new(),
+            destroy_callback: unsafe { mem::zeroed() },
+            is_destroyed: false,
+            is_fallback: false,
+        }
+    }
+
+    pub unsafe fn close_im_if_necessary(&self) -> Result<bool, XError> {
+        if !self.is_destroyed {
+            close_im(&self.xconn, self.im).map(|_| true)
+        } else {
+            Ok(false)
+        }
+    }
+
+    pub unsafe fn destroy_ic_if_necessary(&self, ic: ffi::XIC) -> Result<bool, XError> {
+        if !self.is_destroyed {
+            destroy_ic(&self.xconn, ic).map(|_| true)
+        } else {
+            Ok(false)
+        }
+    }
+
+    pub unsafe fn destroy_all_contexts_if_necessary(&self) -> Result<bool, XError> {
+        for context in self.contexts.values() {
+            if let &Some(ref context) = context {
+                self.destroy_ic_if_necessary(context.ic)?;
+            }
+        }
+        Ok(!self.is_destroyed)
+    }
+}

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

@@ -0,0 +1,277 @@
+use std::env;
+use std::fmt;
+use std::ptr;
+use std::sync::Arc;
+use std::os::raw::c_char;
+use std::ffi::{CStr, CString, IntoStringError};
+
+use super::{ffi, util, XConnection, XError};
+
+unsafe fn open_im(
+    xconn: &Arc<XConnection>,
+    locale_modifiers: &CStr,
+) -> Option<ffi::XIM> {
+    // 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.
+    (xconn.xlib.XSetLocaleModifiers)(locale_modifiers.as_ptr());
+
+    let im = (xconn.xlib.XOpenIM)(
+        xconn.display,
+        ptr::null_mut(),
+        ptr::null_mut(),
+        ptr::null_mut(),
+    );
+
+    if im.is_null() {
+        None
+    } else {
+        Some(im)
+    }
+}
+
+#[derive(Debug)]
+pub struct InputMethod {
+    pub im: ffi::XIM,
+    name: String,
+}
+
+impl InputMethod {
+    fn new(im: ffi::XIM, name: String) -> Self {
+        InputMethod { im, name }
+    }
+}
+
+#[derive(Debug)]
+pub enum InputMethodResult {
+    /// Input method used locale modifier from `XMODIFIERS` environment variable.
+    XModifiers(InputMethod),
+    /// Input method used internal fallback locale modifier.
+    Fallback(InputMethod),
+    /// Input method could not be opened using any locale modifier tried.
+    Failure,
+}
+
+impl InputMethodResult {
+    pub fn is_fallback(&self) -> bool {
+        if let &InputMethodResult::Fallback(_) = self {
+            true
+        } else {
+            false
+        }
+    }
+
+    pub fn ok(self) -> Option<InputMethod> {
+        use self::InputMethodResult::*;
+        match self {
+            XModifiers(im) | Fallback(im) => Some(im),
+            Failure => None,
+        }
+    }
+}
+
+#[derive(Debug, Clone)]
+enum GetXimServersError {
+    XError(XError),
+    GetPropertyError(util::GetPropertyError),
+    InvalidUtf8(IntoStringError),
+}
+
+// The root window has a property named XIM_SERVERS, which contains a list of atoms represeting
+// the availabile XIM servers. For instance, if you're using ibus, it would contain an atom named
+// "@server=ibus". It's possible for this property to contain multiple atoms, though presumably
+// rare. Note that we replace "@server=" with "@im=" in order to match the format of locale
+// modifiers, since we don't want a user who's looking at logs to ask "am I supposed to set
+// XMODIFIERS to `@server=ibus`?!?"
+unsafe fn get_xim_servers(xconn: &Arc<XConnection>) -> Result<Vec<String>, GetXimServersError> {
+    let servers_atom = util::get_atom(&xconn, b"XIM_SERVERS\0")
+        .map_err(GetXimServersError::XError)?;
+
+    let root = (xconn.xlib.XDefaultRootWindow)(xconn.display);
+
+    let mut atoms: Vec<ffi::Atom> = util::get_property(
+        &xconn,
+        root,
+        servers_atom,
+        ffi::XA_ATOM,
+    ).map_err(GetXimServersError::GetPropertyError)?;
+
+    let mut names: Vec<*const c_char> = Vec::with_capacity(atoms.len());
+    (xconn.xlib.XGetAtomNames)(
+        xconn.display,
+        atoms.as_mut_ptr(),
+        atoms.len() as _,
+        names.as_mut_ptr() as _,
+    );
+    names.set_len(atoms.len());
+
+    let mut formatted_names = Vec::with_capacity(names.len());
+    for name in names {
+        let string = CStr::from_ptr(name)
+            .to_owned()
+            .into_string()
+            .map_err(GetXimServersError::InvalidUtf8)?;
+        (xconn.xlib.XFree)(name as _);
+        formatted_names.push(string.replace("@server=", "@im="));
+    }
+    xconn.check_errors().map_err(GetXimServersError::XError)?;
+    Ok(formatted_names)
+}
+
+#[derive(Clone)]
+struct InputMethodName {
+    c_string: CString,
+    string: String,
+}
+
+impl InputMethodName {
+    pub fn from_string(string: String) -> Self {
+        let c_string = CString::new(string.clone())
+            .expect("String used to construct CString contained null byte");
+        InputMethodName {
+            c_string,
+            string,
+        }
+    }
+
+    pub fn from_str(string: &str) -> Self {
+        let c_string = CString::new(string)
+            .expect("String used to construct CString contained null byte");
+        InputMethodName {
+            c_string,
+            string: string.to_owned(),
+        }
+    }
+}
+
+impl fmt::Debug for InputMethodName {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        self.string.fmt(f)
+    }
+}
+
+#[derive(Debug, Clone)]
+struct PotentialInputMethod {
+    name: InputMethodName,
+    successful: Option<bool>,
+}
+
+impl PotentialInputMethod {
+    pub fn from_string(string: String) -> Self {
+        PotentialInputMethod {
+            name: InputMethodName::from_string(string),
+            successful: None,
+        }
+    }
+
+    pub fn from_str(string: &str) -> Self {
+        PotentialInputMethod {
+            name: InputMethodName::from_str(string),
+            successful: None,
+        }
+    }
+
+    pub fn reset(&mut self) {
+        self.successful = None;
+    }
+
+    pub fn open_im(&mut self, xconn: &Arc<XConnection>) -> Option<InputMethod> {
+        let im = unsafe { open_im(xconn, &self.name.c_string) };
+        self.successful = Some(im.is_some());
+        im.map(|im| InputMethod::new(im, self.name.string.clone()))
+    }
+}
+
+// By logging this struct, you get a sequential listing of every locale modifier tried, where it
+// came from, and if it succceeded.
+#[derive(Debug, Clone)]
+pub struct PotentialInputMethods {
+    // On correctly configured systems, the XMODIFIERS environemnt variable tells us everything we
+    // need to know.
+    xmodifiers: Option<PotentialInputMethod>,
+    // We have some standard options at our disposal that should ostensibly always work. For users
+    // who only need compose sequences, this ensures that the program launches without a hitch
+    // For users who need more sophisticated IME features, this is more or less a silent failure.
+    // Logging features should be added in the future to allow both audiences to be effectively
+    // served.
+    fallbacks: [PotentialInputMethod; 2],
+    // For diagnostic purposes, we include the list of XIM servers that the server reports as
+    // being available.
+    _xim_servers: Result<Vec<String>, GetXimServersError>,
+}
+
+impl PotentialInputMethods {
+    pub fn new(xconn: &Arc<XConnection>) -> Self {
+        let xmodifiers = env::var("XMODIFIERS")
+            .ok()
+            .map(PotentialInputMethod::from_string);
+        PotentialInputMethods {
+            // Since passing "" to XSetLocaleModifiers results in it defaulting to the value of
+            // XMODIFIERS, it's worth noting what happens if XMODIFIERS is also "". If simply
+            // running the program with `XMODIFIERS="" cargo run`, then assuming XMODIFIERS is
+            // defined in the profile (or parent environment) then that parent XMODIFIERS is used.
+            // If that XMODIFIERS value is also "" (i.e. if you ran `export XMODIFIERS=""`), then
+            // XSetLocaleModifiers uses the default local input method. Note that defining
+            // XMODIFIERS as "" is different from XMODIFIERS not being defined at all, since in
+            // that case, we get `None` and end up skipping ahead to the next method.
+            xmodifiers,
+            fallbacks: [
+                // This is a standard input method that supports compose equences, which should
+                // always be available. `@im=none` appears to mean the same thing.
+                PotentialInputMethod::from_str("@im=local"),
+                // This explicitly specifies to use the implementation-dependent default, though
+                // that seems to be equivalent to just using the local input method.
+                PotentialInputMethod::from_str("@im="),
+            ],
+            // The XIM_SERVERS property can have surprising values. For instance, when I exited
+            // ibus to run fcitx, it retained the value denoting ibus. Even more surprising is
+            // that the fcitx input method could only be successfully opened using "@im=ibus".
+            // Presumably due to this quirk, it's actually possible to alternate between ibus and
+            // fcitx in a running application.
+            _xim_servers: unsafe { get_xim_servers(xconn) },
+        }
+    }
+
+    // This resets the `successful` field of every potential input method, ensuring we have
+    // accurate information when this struct is re-used by the destruction/instantiation callbacks.
+    fn reset(&mut self) {
+        if let Some(ref mut input_method) = self.xmodifiers {
+            input_method.reset();
+        }
+
+        for input_method in &mut self.fallbacks {
+            input_method.reset();
+        }
+    }
+
+    pub fn open_im(
+        &mut self,
+        xconn: &Arc<XConnection>,
+        callback: Option<&Fn() -> ()>,
+    ) -> InputMethodResult {
+        use self::InputMethodResult::*;
+
+        self.reset();
+
+        if let Some(ref mut input_method) = self.xmodifiers {
+            let im = input_method.open_im(xconn);
+            if let Some(im) = im {
+                return XModifiers(im);
+            } else {
+                if let Some(ref callback) = callback {
+                    callback();
+                }
+            }
+        }
+
+        for input_method in &mut self.fallbacks {
+            let im = input_method.open_im(xconn);
+            if let Some(im) = im {
+                return Fallback(im);
+            }
+        }
+
+        Failure
+    }
+}

src/platform/linux/x11/ime/mod.rs

@@ -0,0 +1,165 @@
+// Important: all XIM calls need to happen from the same thread!
+
+mod inner;
+mod input_method;
+mod context;
+mod callbacks;
+
+use std::sync::Arc;
+use std::sync::mpsc::{Receiver, Sender};
+
+use super::{ffi, util, XConnection, XError};
+
+use self::inner::{close_im, ImeInner};
+use self::input_method::PotentialInputMethods;
+use self::context::{ImeContextCreationError, ImeContext};
+use self::callbacks::*;
+
+pub type ImeReceiver = Receiver<(ffi::Window, i16, i16)>;
+pub type ImeSender = Sender<(ffi::Window, i16, i16)>;
+
+#[derive(Debug)]
+pub enum ImeCreationError {
+    OpenFailure(PotentialInputMethods),
+    SetDestroyCallbackFailed(XError),
+}
+
+pub struct Ime {
+    xconn: Arc<XConnection>,
+    // The actual meat of this struct is boxed away, since it needs to have a fixed location in
+    // memory so we can pass a pointer to it around.
+    inner: Box<ImeInner>,
+}
+
+impl Ime {
+    pub fn new(xconn: Arc<XConnection>) -> Result<Self, ImeCreationError> {
+        let potential_input_methods = PotentialInputMethods::new(&xconn);
+
+        let (mut inner, client_data) = {
+            let mut inner = Box::new(ImeInner::new(
+                xconn,
+                potential_input_methods,
+            ));
+            let inner_ptr = Box::into_raw(inner);
+            let client_data = inner_ptr as _;
+            let destroy_callback = ffi::XIMCallback {
+                client_data,
+                callback: Some(xim_destroy_callback),
+            };
+            inner = unsafe { Box::from_raw(inner_ptr) };
+            inner.destroy_callback = destroy_callback;
+            (inner, client_data)
+        };
+
+        let xconn = Arc::clone(&inner.xconn);
+
+        let input_method = inner.potential_input_methods.open_im(&xconn, Some(&|| {
+            let _ = unsafe { set_instantiate_callback(&xconn, client_data) };
+        }));
+
+        let is_fallback = input_method.is_fallback();
+        if let Some(input_method) = input_method.ok() {
+            inner.im = input_method.im;
+            inner.is_fallback = is_fallback;
+            unsafe {
+                let result = set_destroy_callback(&xconn, input_method.im, &*inner)
+                    .map_err(ImeCreationError::SetDestroyCallbackFailed);
+                if result.is_err() {
+                    let _ = close_im(&xconn, input_method.im);
+                }
+                result?;
+            }
+            Ok(Ime { xconn, inner })
+        } else {
+            Err(ImeCreationError::OpenFailure(inner.potential_input_methods))
+        }
+    }
+
+    pub fn is_destroyed(&self) -> bool {
+        self.inner.is_destroyed
+    }
+
+    // This pattern is used for various methods here:
+    // Ok(_) indicates that nothing went wrong internally
+    // Ok(true) indicates that the action was actually performed
+    // Ok(false) indicates that the action is not presently applicable
+    pub fn create_context(&mut self, window: ffi::Window)
+        -> Result<bool, ImeContextCreationError>
+    {
+        let context = if self.is_destroyed() {
+            // Create empty entry in map, so that when IME is rebuilt, this window has a context.
+            None
+        } else {
+            Some(unsafe { ImeContext::new(
+                &self.inner.xconn,
+                self.inner.im,
+                window,
+                None,
+            ) }?)
+        };
+        self.inner.contexts.insert(window, context);
+        Ok(!self.is_destroyed())
+    }
+
+    pub fn get_context(&self, window: ffi::Window) -> Option<ffi::XIC> {
+        if self.is_destroyed() {
+            return None;
+        }
+        if let Some(&Some(ref context)) = self.inner.contexts.get(&window) {
+            Some(context.ic)
+        } else {
+            None
+        }
+    }
+
+    pub fn remove_context(&mut self, window: ffi::Window) -> Result<bool, XError> {
+        if let Some(Some(context)) = self.inner.contexts.remove(&window) {
+            unsafe {
+                self.inner.destroy_ic_if_necessary(context.ic)?;
+            }
+            Ok(true)
+        } else {
+            Ok(false)
+        }
+    }
+
+    pub fn focus(&mut self, window: ffi::Window) -> Result<bool, XError> {
+        if self.is_destroyed() {
+            return Ok(false);
+        }
+        if let Some(&mut Some(ref mut context)) = self.inner.contexts.get_mut(&window) {
+            context.focus(&self.xconn).map(|_| true)
+        } else {
+            Ok(false)
+        }
+    }
+
+    pub fn unfocus(&mut self, window: ffi::Window) -> Result<bool, XError> {
+        if self.is_destroyed() {
+            return Ok(false);
+        }
+        if let Some(&mut Some(ref mut context)) = self.inner.contexts.get_mut(&window) {
+            context.unfocus(&self.xconn).map(|_| true)
+        } else {
+            Ok(false)
+        }
+    }
+
+    pub fn send_xim_spot(&mut self, window: ffi::Window, x: i16, y: i16) {
+        if self.is_destroyed() {
+            return;
+        }
+        if let Some(&mut Some(ref mut context)) = self.inner.contexts.get_mut(&window) {
+            context.set_spot(&self.xconn, x as _, y as _);
+        }
+    }
+}
+
+impl Drop for Ime {
+    fn drop(&mut self) {
+        unsafe {
+            let _ = self.inner.destroy_all_contexts_if_necessary();
+            let _ = self.inner.close_im_if_necessary();
+        }
+    }
+}

src/platform/linux/x11/mod.rs

@@ -14,22 +14,24 @@ use events::ModifiersState;
 use std::{mem, ptr, slice};
 use std::sync::{Arc, Mutex, Weak};
 use std::sync::atomic::{self, AtomicBool};
-use std::sync::mpsc::{channel, Receiver, Sender};
+use std::sync::mpsc;
 use std::cell::RefCell;
 use std::collections::HashMap;
 use std::ffi::CStr;
 use std::os::raw::{c_char, c_int, c_long, c_uchar, c_uint, c_ulong};
 
-use libc;
+use libc::{self, setlocale, LC_CTYPE};
 
 mod events;
 mod monitor;
 mod window;
 mod xdisplay;
 mod dnd;
+mod ime;
 mod util;
 
 use self::dnd::{Dnd, DndState};
+use self::ime::{ImeReceiver, ImeSender, ImeCreationError, Ime};
 
 // API TRANSITION
 //
@@ -42,9 +44,9 @@ pub struct EventsLoop {
     display: Arc<XConnection>,
     wm_delete_window: ffi::Atom,
     dnd: Dnd,
-    ime_receiver: Receiver<(WindowId, i16, i16)>,
-    ime_sender: Sender<(WindowId, i16, i16)>,
-    ime: RefCell<HashMap<WindowId, util::Ime>>,
+    ime_receiver: ImeReceiver,
+    ime_sender: ImeSender,
+    ime: RefCell<Ime>,
     windows: Arc<Mutex<HashMap<WindowId, WindowData>>>,
     devices: Mutex<HashMap<DeviceId, Device>>,
     xi2ext: XExtension,
@@ -70,7 +72,17 @@ impl EventsLoop {
         let dnd = Dnd::new(Arc::clone(&display))
             .expect("Failed to call XInternAtoms when initializing drag and drop");
 
-        let (ime_sender, ime_receiver) = channel();
+        let (ime_sender, ime_receiver) = mpsc::channel();
+        // Input methods will open successfully without setting the locale, but it won't be
+        // possible to actually commit pre-edit sequences.
+        unsafe { setlocale(LC_CTYPE, b"\0".as_ptr() as *const _); }
+        let ime = RefCell::new({
+            let result = Ime::new(Arc::clone(&display));
+            if let Err(ImeCreationError::OpenFailure(ref state)) = result {
+                panic!(format!("Failed to open input method: {:#?}", state));
+            }
+            result.expect("Failed to set input method destruction callback")
+        });
 
         let xi2ext = unsafe {
             let mut result = XExtension {
@@ -115,7 +127,7 @@ impl EventsLoop {
             dnd,
             ime_receiver,
             ime_sender,
-            ime: RefCell::new(HashMap::new()),
+            ime,
             windows: Arc::new(Mutex::new(HashMap::new())),
             devices: Mutex::new(HashMap::new()),
             xi2ext,
@@ -419,7 +431,10 @@ impl EventsLoop {
 
                 let window = xev.window;
 
-                self.ime.borrow_mut().remove(&WindowId(window));
+                self.ime
+                    .borrow_mut()
+                    .remove_context(window)
+                    .expect("Failed to destroy input context");
             }
 
             ffi::Expose => {
@@ -485,8 +500,8 @@ impl EventsLoop {
                 }
 
                 if state == Pressed {
-                    let written = if let Some(ime) = self.ime.borrow().get(&WindowId(window)) {
-                        unsafe { util::lookup_utf8(&self.display, ime.ic, xkev) }
+                    let written = if let Some(ic) = self.ime.borrow().get_context(window) {
+                        unsafe { util::lookup_utf8(&self.display, ic, xkev) }
                     } else {
                         return;
                     };
@@ -736,11 +751,13 @@ impl EventsLoop {
 
                         let window_id = mkwid(xev.event);
 
-                        if let Some(ime) = self.ime.borrow().get(&WindowId(xev.event)) {
-                            ime.focus().expect("Failed to focus input context");
-                        } else {
+                        if let None = self.windows.lock().unwrap().get(&WindowId(xev.event)) {
                             return;
                         }
+                        self.ime
+                            .borrow_mut()
+                            .focus(xev.event)
+                            .expect("Failed to focus input context");
 
                         callback(Event::WindowEvent { window_id, event: Focused(true) });
 
@@ -764,11 +781,13 @@ impl EventsLoop {
                     ffi::XI_FocusOut => {
                         let xev: &ffi::XIFocusOutEvent = unsafe { &*(xev.data as *const _) };
 
-                        if let Some(ime) = self.ime.borrow().get(&WindowId(xev.event)) {
-                            ime.unfocus().expect("Failed to unfocus input context");
-                        } else {
+                        if let None = self.windows.lock().unwrap().get(&WindowId(xev.event)) {
                             return;
                         }
+                        self.ime
+                            .borrow_mut()
+                            .unfocus(xev.event)
+                            .expect("Failed to unfocus input context");
 
                         callback(Event::WindowEvent {
                             window_id: mkwid(xev.event),
@@ -888,9 +907,7 @@ impl EventsLoop {
 
         match self.ime_receiver.try_recv() {
             Ok((window_id, x, y)) => {
-                if let Some(ime) = self.ime.borrow_mut().get_mut(&window_id) {
-                    ime.send_xim_spot(x, y);
-                }
+                self.ime.borrow_mut().send_xim_spot(window_id, x, y);
             }
             Err(_) => ()
         }
@@ -987,7 +1004,7 @@ pub struct Window {
     pub window: Arc<Window2>,
     display: Weak<XConnection>,
     windows: Weak<Mutex<HashMap<WindowId, WindowData>>>,
-    ime_sender: Sender<(WindowId, i16, i16)>,
+    ime_sender: ImeSender,
 }
 
 impl ::std::ops::Deref for Window {
@@ -1006,9 +1023,10 @@ impl Window {
     ) -> Result<Self, CreationError> {
         let win = Arc::new(try!(Window2::new(&x_events_loop, window, pl_attribs)));
 
-        let ime = util::Ime::new(Arc::clone(&x_events_loop.display), win.id().0)
-            .expect("Failed to initialize IME");
-        x_events_loop.ime.borrow_mut().insert(win.id(), ime);
+        x_events_loop.ime
+            .borrow_mut()
+            .create_context(win.id().0)
+            .expect("Failed to create input context");
 
         x_events_loop.windows.lock().unwrap().insert(win.id(), WindowData {
             config: None,
@@ -1031,7 +1049,7 @@ impl Window {
 
     #[inline]
     pub fn send_xim_spot(&self, x: i16, y: i16) {
-        let _ = self.ime_sender.send((self.window.id(), x, y));
+        let _ = self.ime_sender.send((self.window.id().0, x, y));
     }
 }
 

src/platform/linux/x11/util.rs

@@ -90,7 +90,7 @@ pub unsafe fn send_client_msg(
     xconn.check_errors().map(|_| ())
 }
 
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub enum GetPropertyError {
     XError(XError),
     TypeMismatch(ffi::Atom),
@@ -309,7 +309,6 @@ pub unsafe fn lookup_utf8(
     str::from_utf8(&buffer[..count as usize]).unwrap_or("").to_string()
 }
 
-
 #[derive(Debug)]
 pub struct FrameExtents {
     pub left: c_ulong,
@@ -364,114 +363,3 @@ impl WindowGeometry {
         )
     }
 }
-
-// Important: all XIM calls need to happen from the same thread!
-pub struct Ime {
-    xconn: Arc<XConnection>,
-    pub im: ffi::XIM,
-    pub ic: ffi::XIC,
-    ic_spot: ffi::XPoint,
-}
-
-impl Ime {
-    pub fn new(xconn: Arc<XConnection>, window: ffi::Window) -> Option<Self> {
-        let im = unsafe {
-            let mut im: ffi::XIM = ptr::null_mut();
-
-            // Setting an empty string as the locale modifier results in the user's XMODIFIERS
-            // environment variable being read, which should result in the user's configured input
-            // method (ibus, fcitx, etc.) being used. If that fails, we fall back to internal
-            // input methods which should always be available, though only support compose keys.
-            for modifiers in &[b"\0" as &[u8], b"@im=local\0", b"@im=\0"] {
-                if !im.is_null() {
-                    break;
-                }
-
-                (xconn.xlib.XSetLocaleModifiers)(modifiers.as_ptr() as *const _);
-                im = (xconn.xlib.XOpenIM)(
-                    xconn.display,
-                    ptr::null_mut(),
-                    ptr::null_mut(),
-                    ptr::null_mut(),
-                );
-            }
-
-            if im.is_null() {
-                return None;
-            }
-
-            im
-        };
-
-        let ic = unsafe {
-            let ic = (xconn.xlib.XCreateIC)(
-                im,
-                b"inputStyle\0".as_ptr() as *const _,
-                ffi::XIMPreeditNothing | ffi::XIMStatusNothing,
-                b"clientWindow\0".as_ptr() as *const _,
-                window,
-                ptr::null::<()>(),
-            );
-            if ic.is_null() {
-                return None;
-            }
-            (xconn.xlib.XSetICFocus)(ic);
-            xconn.check_errors().expect("Failed to call XSetICFocus");
-            ic
-        };
-
-        Some(Ime {
-            xconn,
-            im,
-            ic,
-            ic_spot: ffi::XPoint { x: 0, y: 0 },
-        })
-    }
-
-    pub fn focus(&self) -> Result<(), XError> {
-        unsafe {
-            (self.xconn.xlib.XSetICFocus)(self.ic);
-        }
-        self.xconn.check_errors()
-    }
-
-    pub fn unfocus(&self) -> Result<(), XError> {
-        unsafe {
-            (self.xconn.xlib.XUnsetICFocus)(self.ic);
-        }
-        self.xconn.check_errors()
-    }
-
-    pub fn send_xim_spot(&mut self, x: i16, y: i16) {
-        let nspot = ffi::XPoint { x: x as _, y: y as _ };
-        if self.ic_spot.x == x && self.ic_spot.y == y {
-            return;
-        }
-        self.ic_spot = nspot;
-        unsafe {
-            let preedit_attr = (self.xconn.xlib.XVaCreateNestedList)(
-                0,
-                b"spotLocation\0",
-                &nspot,
-                ptr::null::<()>(),
-            );
-            (self.xconn.xlib.XSetICValues)(
-                self.ic,
-                b"preeditAttributes\0",
-                preedit_attr,
-                ptr::null::<()>(),
-            );
-            (self.xconn.xlib.XFree)(preedit_attr);
-        }
-    }
-}
-
-impl Drop for Ime {
-    fn drop(&mut self) {
-        unsafe {
-            (self.xconn.xlib.XDestroyIC)(self.ic);
-            (self.xconn.xlib.XCloseIM)(self.im);
-        }
-        self.xconn.check_errors().expect("Failed to close input method");
-    }
-}