it: test window gains kb focus when mapped

src/utils/once.rs

@@ -0,0 +1,26 @@
+#![allow(dead_code)]
+
+use std::{cell::Cell, future::Future};
+
+#[derive(Default)]
+pub struct Once {
+    done: Cell<bool>,
+}
+
+impl Once {
+    pub fn set(&self) -> bool {
+        !self.done.replace(true)
+    }
+
+    pub fn exec<F: FnOnce()>(&self, f: F) {
+        if !self.done.replace(true) {
+            f();
+        }
+    }
+
+    pub async fn exec_async<G: Future<Output = ()>, F: FnOnce() -> G>(&self, f: F) {
+        if !self.done.replace(true) {
+            f().await;
+        }
+    }
+}