From 0863715890f7d4d88b093fc2c4df138402cfcecf Mon Sep 17 00:00:00 2001
From: Greg V <greg@unrelenting.technology>
Date: Fri, 20 Nov 2020 20:04:51 +0300
Subject: [PATCH] keyboard: use SmallVec for the Enter event's currently
 pressed keys

The Event enum used string slices referencing stack-allocated Vecs (that were not reused anywhere else).
The lifetime makes it awkward for consumers (no way to e.g. store the Event somewhere) but I doubt
that it was a useful optimization (even if the optimizer can't allocate the Vec directly in the resulting enum,
creating a slice of it is hardly better than moving it: you still write the address and size, just not the capacity).

However, we can use SmallVec (already a dependency of wayland-rs) for an actual optimization:
this will avoid allocating Vec contents if 1-2 keys are held when the surface gets keyboard focus.
---
 Cargo.toml               |  1 +
 src/seat/keyboard/mod.rs | 23 ++++++++++++-----------
 2 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index c8edbce97..2ecc0e8ac 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -24,6 +24,7 @@ wayland-protocols = { version = "0.28" , features = ["client", "unstable_protoco
 wayland-cursor = "0.28"
 calloop = { version = "0.6.1", optional = true }
 byteorder = "1.0"
+smallvec = "1"
 
 [features]
 default = ["frames", "calloop"]
diff --git a/src/seat/keyboard/mod.rs b/src/seat/keyboard/mod.rs
index 1e4b8b864..4cc31f4f9 100644
--- a/src/seat/keyboard/mod.rs
+++ b/src/seat/keyboard/mod.rs
@@ -24,6 +24,7 @@ use std::{
 };
 
 use byteorder::{ByteOrder, NativeEndian};
+use smallvec::SmallVec;
 
 pub use wayland_client::protocol::wl_keyboard::KeyState;
 use wayland_client::{
@@ -70,7 +71,7 @@ pub enum Error {
 }
 
 /// Events received from a mapped keyboard
-pub enum Event<'a> {
+pub enum Event {
     /// The keyboard focus has entered a surface
     Enter {
         /// serial number of the event
@@ -78,9 +79,9 @@ pub enum Event<'a> {
         /// surface that was entered
         surface: wl_surface::WlSurface,
         /// raw values of the currently pressed keys
-        rawkeys: &'a [u32],
+        rawkeys: SmallVec<[u32; 2]>,
         /// interpreted symbols of the currently pressed keys
-        keysyms: &'a [u32],
+        keysyms: SmallVec<[u32; 2]>,
     },
     /// The keyboard focus has left a surface
     Leave {
@@ -142,7 +143,7 @@ pub fn map_keyboard<F>(
     callback: F,
 ) -> Result<wl_keyboard::WlKeyboard, Error>
 where
-    F: FnMut(Event<'_>, wl_keyboard::WlKeyboard, wayland_client::DispatchData<'_>) + 'static,
+    F: FnMut(Event, wl_keyboard::WlKeyboard, wayland_client::DispatchData<'_>) + 'static,
 {
     let has_kbd = super::with_seat_data(seat, |data| data.has_keyboard).unwrap_or(false);
     let keyboard = if has_kbd {
@@ -191,7 +192,7 @@ pub fn map_keyboard_repeat<F, Data: 'static>(
     callback: F,
 ) -> Result<(wl_keyboard::WlKeyboard, calloop::Source<RepeatSource>), Error>
 where
-    F: FnMut(Event<'_>, wl_keyboard::WlKeyboard, wayland_client::DispatchData<'_>) + 'static,
+    F: FnMut(Event, wl_keyboard::WlKeyboard, wayland_client::DispatchData<'_>) + 'static,
 {
     let has_kbd = super::with_seat_data(seat, |data| data.has_keyboard).unwrap_or(false);
     let keyboard = if has_kbd {
@@ -264,7 +265,7 @@ fn rate_to_gap(rate: i32) -> Option<NonZeroU32> {
  * Classic handling
  */
 
-type KbdCallback = dyn FnMut(Event<'_>, wl_keyboard::WlKeyboard, wayland_client::DispatchData<'_>);
+type KbdCallback = dyn FnMut(Event, wl_keyboard::WlKeyboard, wayland_client::DispatchData<'_>);
 
 #[cfg(feature = "calloop")]
 struct RepeatDetails {
@@ -393,10 +394,10 @@ impl KbdHandler {
         dispatch_data: wayland_client::DispatchData,
     ) {
         let mut state = self.state.borrow_mut();
-        let rawkeys = keys.chunks_exact(4).map(NativeEndian::read_u32).collect::<Vec<_>>();
-        let keys: Vec<u32> = rawkeys.iter().map(|k| state.get_one_sym_raw(*k)).collect();
+        let rawkeys = keys.chunks_exact(4).map(NativeEndian::read_u32).collect::<SmallVec<_>>();
+        let keysyms = rawkeys.iter().map(|k| state.get_one_sym_raw(*k)).collect();
         (&mut *self.callback.borrow_mut())(
-            Event::Enter { serial, surface, rawkeys: &rawkeys, keysyms: &keys },
+            Event::Enter { serial, surface, rawkeys, keysyms },
             object,
             dispatch_data,
         );
@@ -552,7 +553,7 @@ pub struct RepeatSource {
 
 #[cfg(feature = "calloop")]
 impl calloop::EventSource for RepeatSource {
-    type Event = Event<'static>;
+    type Event = Event;
     type Metadata = wl_keyboard::WlKeyboard;
     type Ret = ();
 
@@ -563,7 +564,7 @@ impl calloop::EventSource for RepeatSource {
         mut callback: F,
     ) -> std::io::Result<()>
     where
-        F: FnMut(Event<'static>, &mut wl_keyboard::WlKeyboard),
+        F: FnMut(Event, &mut wl_keyboard::WlKeyboard),
     {
         let current_repeat = &self.current_repeat;
         let state = &self.state;