Interleave pressing/releasing of modifier keys. (#208)

* Interleave pressing/releasing of modifier keys.

Pressing new modifier keys before releasing the old ones to avoid
triggering actions in applications that recognize the old keys.

For example, if we bind alt+f to ctrl+right, before this change, the
following key sequence is generated with alt+f:

(user)       send Alt_L      PRESS
(xremap)     send Alt_L      RELEASE
(xremap)     send Control_L  PRESS
(xremap)     send Right      PRESS
(xremap)     send Right      RELEASE
(xremap)     send Control_L  RELEASE
(xremap)     send Alt_L      PRESS
(user)       send Alt_L      RELEASE

The press + release of the alt key (both at the start and end of the
sequence) is causing apps like Firefox to show/focus the menu bar.

After this change, the following key sequence is generated with alt+f:

(user)       send Alt_L      PRESS
(xremap)     send Control_L  PRESS
(xremap)     send Alt_L      RELEASE
(xremap)     send Right      PRESS
(xremap)     send Right      RELEASE
(xremap)     send Alt_L      PRESS
(xremap)     send Control_L  RELEASE
(user)       send Alt_L      RELEASE

So the difference here is that we press the ctrl key before releasing
alt, so will not trigger apps like Firefox to show hide the menu when
alt+f is used, and a single press and release of the alt key will
still show the menu as their normal behavior.

As far as I can observe, this is also the behavior of AutoHotKey on Windows.

* Add test.

src/event_handler.rs

@@ -343,8 +343,8 @@ impl EventHandler {
         missing_modifiers.retain(|key| MODIFIER_KEYS.contains(&key));
 
         // Emulate the modifiers of KeyPress
-        self.send_keys(&extra_modifiers, RELEASE);
         self.send_keys(&missing_modifiers, PRESS);
+        self.send_keys(&extra_modifiers, RELEASE);
 
         // Press the main key
         self.send_key(&key_press.key, PRESS);
@@ -353,8 +353,8 @@ impl EventHandler {
         self.send_action(Action::Delay(self.keypress_delay));
 
         // Resurrect the original modifiers
-        self.send_keys(&missing_modifiers, RELEASE);
         self.send_keys(&extra_modifiers, PRESS);
+        self.send_keys(&missing_modifiers, RELEASE);
     }
 
     fn with_mark(&self, key_press: &KeyPress) -> KeyPress {

src/tests.rs

@@ -5,7 +5,7 @@ use std::time::Duration;
 
 use crate::{
     action::Action,
-    config::Config,
+    config::{keymap::build_keymap_table, Config},
     event::{Event, KeyEvent, KeyValue},
     event_handler::EventHandler,
 };
@@ -33,9 +33,35 @@ fn test_basic_modmap() {
     )
 }
 
+#[test]
+fn test_interleave_modifiers() {
+    assert_actions(
+        indoc! {"
+        keymap:
+          - remap:
+              M-f: C-right
+        "},
+        vec![
+            Event::KeyEvent(KeyEvent::new(Key::KEY_LEFTALT, KeyValue::Press)),
+            Event::KeyEvent(KeyEvent::new(Key::KEY_F, KeyValue::Press)),
+        ],
+        vec![
+            Action::KeyEvent(KeyEvent::new(Key::KEY_LEFTALT, KeyValue::Press)),
+            Action::KeyEvent(KeyEvent::new(Key::KEY_LEFTCTRL, KeyValue::Press)),
+            Action::KeyEvent(KeyEvent::new(Key::KEY_LEFTALT, KeyValue::Release)),
+            Action::KeyEvent(KeyEvent::new(Key::KEY_RIGHT, KeyValue::Press)),
+            Action::KeyEvent(KeyEvent::new(Key::KEY_RIGHT, KeyValue::Release)),
+            Action::Delay(Duration::from_nanos(0)),
+            Action::KeyEvent(KeyEvent::new(Key::KEY_LEFTALT, KeyValue::Press)),
+            Action::KeyEvent(KeyEvent::new(Key::KEY_LEFTCTRL, KeyValue::Release)),
+        ],
+    )
+}
+
 fn assert_actions(config_yaml: &str, events: Vec<Event>, actions: Vec<Action>) {
     let timer = TimerFd::new(ClockId::CLOCK_MONOTONIC, TimerFlags::empty()).unwrap();
-    let config: Config = serde_yaml::from_str(config_yaml).unwrap();
+    let mut config: Config = serde_yaml::from_str(config_yaml).unwrap();
+    config.keymap_table = build_keymap_table(&config.keymap);
     let mut event_handler = EventHandler::new(timer, "default", Duration::from_micros(0));
     let mut actual: Vec<Action> = vec![];
     for event in &events {