Add debounce-ms recent-windows setting

docs/wiki/Configuration:-Recent-Windows.md

@@ -9,6 +9,8 @@ Here is an outline of the available settings and their default values:
 ```kdl
 recent-windows {
     // off
+    debounce-ms 750
+
     open-delay-ms 150
 
     highlight {
@@ -39,6 +41,30 @@ recent-windows {
 
 `off` disables the recent windows switcher altogether.
 
+### `debounce-ms`
+
+Delay, in milliseconds, between the window receiving focus and getting "committed" to the recent windows list.
+
+When you want to focus some window, you might end up focusing some unrelated windows on the way:
+
+- with keyboard navigation, the windows between your current one and the target one;
+- with [`focus-follows-mouse`](./Configuration:-Input.md#focus-follows-mouse), the windows you happen to cross with the mouse pointer on the way to the target window.
+
+The debounce delay prevents those intermediate windows from polluting the recent windows list.
+
+Note that some actions, like keyboard input into the target window, will skip this delay and commit the window to the list immediately.
+This way, the recent windows list stays responsive while not getting polluted too much with unintended windows.
+
+If you want windows to appear in recent windows right away, including intermediate windows, you can reduce the delay or set it to zero:
+
+```kdl
+recent-windows {
+    // Commit windows to the recent windows list as soon as they're focused,
+    // with no debounce delay.
+    debounce-ms 0
+}
+```
+
 ### `open-delay-ms`
 
 Delay, in milliseconds, between pressing the Alt-Tab bind and the recent windows switcher visually appearing on screen.

niri-config/src/lib.rs

@@ -56,9 +56,7 @@ pub use crate::layout::*;
 pub use crate::misc::*;
 pub use crate::output::{Output, OutputName, Outputs, Position, Vrr};
 use crate::recent_windows::RecentWindowsPart;
-pub use crate::recent_windows::{
-    MruDirection, MruFilter, MruPreviews, MruScope, RecentWindows, DEFAULT_MRU_COMMIT_MS,
-};
+pub use crate::recent_windows::{MruDirection, MruFilter, MruPreviews, MruScope, RecentWindows};
 pub use crate::utils::FloatOrInt;
 use crate::utils::{Flag, MergeWith as _};
 pub use crate::window_rule::{FloatingPosition, RelativeTo, WindowRule};
@@ -2181,6 +2179,7 @@ mod tests {
             ],
             recent_windows: RecentWindows {
                 on: false,
+                debounce_ms: 750,
                 open_delay_ms: 150,
                 highlight: MruHighlight {
                     active_color: Color {

niri-config/src/recent_windows.rs

@@ -6,13 +6,10 @@ use smithay::input::keyboard::Keysym;
 use crate::utils::{expect_only_children, MergeWith};
 use crate::{Action, Bind, Color, FloatOrInt, Key, Modifiers, Trigger};
 
-/// Delay before the window focus is considered to be locked-in for Window
-/// MRU ordering. For now the delay is not configurable.
-pub const DEFAULT_MRU_COMMIT_MS: u64 = 750;
-
 #[derive(Debug, PartialEq)]
 pub struct RecentWindows {
     pub on: bool,
+    pub debounce_ms: u16,
     pub open_delay_ms: u16,
     pub highlight: MruHighlight,
     pub previews: MruPreviews,
@@ -23,6 +20,7 @@ impl Default for RecentWindows {
     fn default() -> Self {
         RecentWindows {
             on: true,
+            debounce_ms: 750,
             open_delay_ms: 150,
             highlight: MruHighlight::default(),
             previews: MruPreviews::default(),
@@ -38,6 +36,8 @@ pub struct RecentWindowsPart {
     #[knuffel(child)]
     pub off: bool,
     #[knuffel(child, unwrap(argument))]
+    pub debounce_ms: Option<u16>,
+    #[knuffel(child, unwrap(argument))]
     pub open_delay_ms: Option<u16>,
     #[knuffel(child)]
     pub highlight: Option<MruHighlightPart>,
@@ -54,7 +54,7 @@ impl MergeWith<RecentWindowsPart> for RecentWindows {
             self.on = false;
         }
 
-        merge_clone!((self, part), open_delay_ms);
+        merge_clone!((self, part), debounce_ms, open_delay_ms);
         merge!((self, part), highlight, previews);
 
         if let Some(part) = &part.binds {

src/niri.rs

@@ -16,7 +16,7 @@ use calloop::futures::Scheduler;
 use niri_config::debug::PreviewRender;
 use niri_config::{
     Config, FloatOrInt, Key, Modifiers, OutputName, TrackLayout, WarpMouseToFocusMode,
-    WorkspaceReference, Xkb, DEFAULT_MRU_COMMIT_MS,
+    WorkspaceReference, Xkb,
 };
 use smithay::backend::allocator::Fourcc;
 use smithay::backend::input::Keycode;
@@ -1255,11 +1255,13 @@ impl State {
                     // period has gone by without the focus having elsewhere.
                     let stamp = get_monotonic_time();
 
-                    if mapped.get_focus_timestamp().is_none() {
+                    let debounce = self.niri.config.borrow().recent_windows.debounce_ms;
+                    let debounce = Duration::from_millis(u64::from(debounce));
+
+                    if mapped.get_focus_timestamp().is_none() || debounce.is_zero() {
                         mapped.set_focus_timestamp(stamp);
                     } else {
-                        let timer =
-                            Timer::from_duration(Duration::from_millis(DEFAULT_MRU_COMMIT_MS));
+                        let timer = Timer::from_duration(debounce);
 
                         let focus_token = self
                             .niri