add caret blink to input

crates/core/tests/input.rs

@@ -262,6 +262,44 @@ fn read_only_refuses_edits_but_keeps_selection_and_copy() {
             .unwrap_or_default()
     });
     assert_eq!(clipboard, "lo");
+
+    // The caret is suppressed entirely while read-only.
+    let caret = cx.update(|cx| state.update(cx, |state, cx| state.caret_visible(true, cx)));
+    assert!(!caret);
+}
+
+#[test]
+fn caret_blinks_while_focused_and_holds_solid_while_typing() {
+    let (cx, state, mut visual) = input_window("", false);
+    focus(&mut visual, &state);
+    visual.update(|window, cx| {
+        window.draw(cx).clear(cx);
+    });
+    visual.run_until_parked();
+
+    let caret = || cx.update(|cx| state.update(cx, |state, cx| state.caret_visible(true, cx)));
+
+    // The caret shows on focus, hides after one interval, and reappears
+    // after another.
+    assert!(caret());
+    cx.executor().advance_clock(Duration::from_millis(500));
+    visual.run_until_parked();
+    assert!(!caret());
+    cx.executor().advance_clock(Duration::from_millis(500));
+    visual.run_until_parked();
+    assert!(caret());
+
+    // Typing holds the caret solid and restarts the cycle.
+    visual.simulate_keystrokes("a");
+    assert!(caret());
+    cx.executor().advance_clock(Duration::from_millis(500));
+    visual.run_until_parked();
+    assert!(!caret());
+
+    // An unfocused field reports no caret.
+    let caret_unfocused =
+        cx.update(|cx| state.update(cx, |state, cx| state.caret_visible(false, cx)));
+    assert!(!caret_unfocused);
 }
 
 #[test]