Implemented focus_window (#1944)

src/platform_impl/linux/mod.rs

@@ -430,6 +430,14 @@ impl Window {
     }
 
     #[inline]
+    pub fn focus_window(&self) {
+        match self {
+            #[cfg(feature = "x11")]
+            &Window::X(ref w) => w.focus_window(),
+            #[cfg(feature = "wayland")]
+            _ => (),
+        }
+    }
     pub fn request_user_attention(&self, _request_type: Option<UserAttentionType>) {
         match self {
             #[cfg(feature = "x11")]

src/platform_impl/linux/x11/ffi.rs

@@ -1,4 +1,9 @@
+use x11_dl::xmd::CARD32;
 pub use x11_dl::{
     error::OpenError, keysym::*, xcursor::*, xinput::*, xinput2::*, xlib::*, xlib_xcb::*,
     xrandr::*, xrender::*,
 };
+
+// Isn't defined by x11_dl
+#[allow(non_upper_case_globals)]
+pub const IconicState: CARD32 = 3;

src/platform_impl/linux/x11/window.rs

@@ -1340,6 +1340,41 @@ impl UnownedWindow {
         self.set_ime_position_physical(x, y);
     }
 
+    #[inline]
+    pub fn focus_window(&self) {
+        let state_atom = unsafe { self.xconn.get_atom_unchecked(b"WM_STATE\0") };
+        let state_type_atom = unsafe { self.xconn.get_atom_unchecked(b"CARD32\0") };
+        let is_minimized = if let Ok(state) =
+            self.xconn
+                .get_property(self.xwindow, state_atom, state_type_atom)
+        {
+            state.contains(&(ffi::IconicState as c_ulong))
+        } else {
+            false
+        };
+        let is_visible = match self.shared_state.lock().visibility {
+            Visibility::Yes => true,
+            Visibility::YesWait | Visibility::No => false,
+        };
+
+        if is_visible && !is_minimized {
+            let atom = unsafe { self.xconn.get_atom_unchecked(b"_NET_ACTIVE_WINDOW\0") };
+            let flusher = self.xconn.send_client_msg(
+                self.xwindow,
+                self.root,
+                atom,
+                Some(ffi::SubstructureRedirectMask | ffi::SubstructureNotifyMask),
+                [1, ffi::CurrentTime as c_long, 0, 0, 0],
+            );
+            if let Err(e) = flusher.flush() {
+                log::error!(
+                    "`flush` returned an error when focusing the window. Error was: {}",
+                    e
+                );
+            }
+        }
+    }
+
     #[inline]
     pub fn request_user_attention(&self, request_type: Option<UserAttentionType>) {
         let mut wm_hints = self