zmk: Layer change event zmk_layer_state_changed for layer 0 inconsistent

In looking at Layer change event I noticed there is a zmk_layer_state_changed event for layer 0 the first time a transition is made back to it but no reports when it is initially activated or when it is subsequently returned to.

I noticed this when I was trying to set layer leds based on the zmk_layer_state_changed event.

My key board has the mapping between layers set to: &to 1 -> &to 2 -> &to 3 -> &to 0

In the logs below you can see the first transition from layer 3->0 is reported but the subsequent one is not. Note I added the zmk_layer_state_changed_listener log message just before the event is sent.

Here’s the patch I’d propose, see any issues with this?

diff --git a/app/src/keymap.c b/app/src/keymap.c
index 75ec6bf..7567d7f 100644
--- a/app/src/keymap.c
+++ b/app/src/keymap.c
@@ -19,8 +19,9 @@ LOG_MODULE_DECLARE(zmk, CONFIG_ZMK_LOG_LEVEL);
 #include <zmk/events/layer_state_changed.h>
 #include <zmk/events/sensor_event.h>
 
-static zmk_keymap_layers_state_t _zmk_keymap_layer_state = 0;
-static uint8_t _zmk_keymap_layer_default = 0;
+static const uint8_t _zmk_keymap_layer_default = 0;
+static zmk_keymap_layers_state_t _zmk_keymap_layer_state = BIT(_zmk_keymap_layer_default);
+
 
 #define DT_DRV_COMPAT zmk_keymap
 
@@ -87,7 +88,7 @@ static inline int set_layer_state(uint8_t layer, bool state) {
     zmk_keymap_layers_state_t old_state = _zmk_keymap_layer_state;
     WRITE_BIT(_zmk_keymap_layer_state, layer, state);
     // Don't send state changes unless there was an actual change
-    if (old_state != _zmk_keymap_layer_state) {
+    if (old_state != _zmk_keymap_layer_state || layer == _zmk_keymap_layer_default) {
         LOG_DBG("layer_changed: layer %d state %d", layer, state);
         ZMK_EVENT_RAISE(create_layer_state_changed(layer, state));
     }

[00:00:14.607,574] <dbg> zmk.position_state_changed_listener: 17 bubble (no undecided hold_tap active)
[00:00:14.607,604] <dbg> zmk.zmk_event_manager_handle_from: Listener captured the event
[00:00:14.711,944] <dbg> zmk.zmk_keymap_apply_position_state: layer: 0 position: 17, binding name: TO_LAYER
[00:00:14.711,975] <dbg> zmk.to_keymap_binding_pressed: position 17 layer 1
[00:00:14.711,975] <dbg> zmk.set_layer_state: layer_changed: layer 1 state 1
[00:00:14.712,005] <dbg> zmk.layer_event_listener: *****zmk_layer_state_changed listener: 1 1
[00:00:15.220,367] <dbg> zmk.kscan_gpio_read_0: Sending event at 5,13 state off
[00:00:15.220,458] <dbg> zmk.zmk_kscan_process_msgq: Row: 5, col: 13, position: 17, pressed: false

[00:00:15.220,489] <dbg> zmk.position_state_changed_listener: 17 bubble (no undecided hold_tap active)
[00:00:15.220,520] <dbg> zmk.zmk_keymap_apply_position_state: layer: 0 position: 17, binding name: TO_LAYER
[00:00:15.220,550] <dbg> zmk.to_keymap_binding_released: position 17 layer 1
[00:00:15.911,407] <dbg> zmk.kscan_gpio_read_0: Sending event at 5,13 state on
[00:00:15.911,468] <dbg> zmk.zmk_kscan_process_msgq: Row: 5, col: 13, position: 17, pressed: true

[00:00:15.911,499] <dbg> zmk.position_state_changed_listener: 17 bubble (no undecided hold_tap active)
[00:00:15.911,529] <dbg> zmk.zmk_event_manager_handle_from: Listener captured the event
[00:00:16.015,686] <dbg> zmk.zmk_keymap_apply_position_state: layer: 1 position: 17, binding name: TO_LAYER
[00:00:16.015,747] <dbg> zmk.to_keymap_binding_pressed: position 17 layer 2
[00:00:16.015,747] <dbg> zmk.set_layer_state: layer_changed: layer 1 state 0
[00:00:16.015,777] <dbg> zmk.layer_event_listener: *****zmk_layer_state_changed listener: 1 0
[00:00:16.015,777] <dbg> zmk.set_layer_state: layer_changed: layer 2 state 1
[00:00:16.015,808] <dbg> zmk.layer_event_listener: *****zmk_layer_state_changed listener: 2 1
[00:00:16.523,895] <dbg> zmk.kscan_gpio_read_0: Sending event at 5,13 state off
[00:00:16.523,986] <dbg> zmk.zmk_kscan_process_msgq: Row: 5, col: 13, position: 17, pressed: false

[00:00:16.524,017] <dbg> zmk.position_state_changed_listener: 17 bubble (no undecided hold_tap active)
[00:00:16.524,047] <dbg> zmk.zmk_keymap_apply_position_state: layer: 1 position: 17, binding name: TO_LAYER
[00:00:16.524,078] <dbg> zmk.to_keymap_binding_released: position 17 layer 2
[00:00:16.727,386] <dbg> zmk.kscan_gpio_read_0: Sending event at 5,13 state on
[00:00:16.727,447] <dbg> zmk.zmk_kscan_process_msgq: Row: 5, col: 13, position: 17, pressed: true

[00:00:16.727,478] <dbg> zmk.position_state_changed_listener: 17 bubble (no undecided hold_tap active)
[00:00:16.727,478] <dbg> zmk.zmk_event_manager_handle_from: Listener captured the event
[00:00:16.831,695] <dbg> zmk.zmk_keymap_apply_position_state: layer: 2 position: 17, binding name: TO_LAYER
[00:00:16.831,756] <dbg> zmk.to_keymap_binding_pressed: position 17 layer 3
[00:00:16.831,756] <dbg> zmk.set_layer_state: layer_changed: layer 2 state 0
[00:00:16.831,787] <dbg> zmk.layer_event_listener: *****zmk_layer_state_changed listener: 2 0
[00:00:16.831,787] <dbg> zmk.set_layer_state: layer_changed: layer 3 state 1
[00:00:16.831,817] <dbg> zmk.layer_event_listener: *****zmk_layer_state_changed listener: 3 1
[00:00:17.339,904] <dbg> zmk.kscan_gpio_read_0: Sending event at 5,13 state off
[00:00:17.339,996] <dbg> zmk.zmk_kscan_process_msgq: Row: 5, col: 13, position: 17, pressed: false

[00:00:17.340,026] <dbg> zmk.position_state_changed_listener: 17 bubble (no undecided hold_tap active)
[00:00:17.340,057] <dbg> zmk.zmk_keymap_apply_position_state: layer: 2 position: 17, binding name: TO_LAYER
[00:00:17.340,087] <dbg> zmk.to_keymap_binding_released: position 17 layer 3
[00:00:17.657,531] <dbg> zmk.kscan_gpio_read_0: Sending event at 5,13 state on
[00:00:17.657,562] <dbg> zmk.zmk_kscan_process_msgq: Row: 5, col: 13, position: 17, pressed: true

[00:00:17.657,592] <dbg> zmk.position_state_changed_listener: 17 bubble (no undecided hold_tap active)
[00:00:17.657,623] <dbg> zmk.zmk_event_manager_handle_from: Listener captured the event
[00:00:17.762,207] <dbg> zmk.zmk_keymap_apply_position_state: layer: 3 position: 17, binding name: TO_LAYER
[00:00:17.762,268] <dbg> zmk.to_keymap_binding_pressed: position 17 layer 0
[00:00:17.762,268] <dbg> zmk.set_layer_state: layer_changed: layer 3 state 0
[00:00:17.762,298] <dbg> zmk.layer_event_listener: *****zmk_layer_state_changed listener: 3 0
[00:00:17.762,329] <dbg> zmk.set_layer_state: layer_changed: layer 0 state 1
[00:00:17.762,329] <dbg> zmk.layer_event_listener: *****zmk_layer_state_changed listener: 0 1
[00:00:18.270,599] <dbg> zmk.kscan_gpio_read_0: Sending event at 5,13 state off
[00:00:18.270,690] <dbg> zmk.zmk_kscan_process_msgq: Row: 5, col: 13, position: 17, pressed: false

[00:00:18.270,721] <dbg> zmk.position_state_changed_listener: 17 bubble (no undecided hold_tap active)
[00:00:18.270,751] <dbg> zmk.zmk_keymap_apply_position_state: layer: 3 position: 17, binding name: TO_LAYER
[00:00:18.270,782] <dbg> zmk.to_keymap_binding_released: position 17 layer 0
[00:00:24.537,322] <dbg> zmk.kscan_gpio_read_0: Sending event at 5,13 state on
[00:00:24.537,353] <dbg> zmk.zmk_kscan_process_msgq: Row: 5, col: 13, position: 17, pressed: true

[00:00:24.537,414] <dbg> zmk.position_state_changed_listener: 17 bubble (no undecided hold_tap active)
[00:00:24.537,414] <dbg> zmk.zmk_event_manager_handle_from: Listener captured the event
[00:00:24.641,632] <dbg> zmk.zmk_keymap_apply_position_state: layer: 0 position: 17, binding name: TO_LAYER
[00:00:24.641,662] <dbg> zmk.to_keymap_binding_pressed: position 17 layer 1
[00:00:24.641,693] <dbg> zmk.set_layer_state: layer_changed: layer 1 state 1
[00:00:24.641,723] <dbg> zmk.layer_event_listener: *****zmk_layer_state_changed listener: 1 1
[00:00:25.149,810] <dbg> zmk.kscan_gpio_read_0: Sending event at 5,13 state off
[00:00:25.149,902] <dbg> zmk.zmk_kscan_process_msgq: Row: 5, col: 13, position: 17, pressed: false

[00:00:25.149,932] <dbg> zmk.position_state_changed_listener: 17 bubble (no undecided hold_tap active)
[00:00:25.149,963] <dbg> zmk.zmk_keymap_apply_position_state: layer: 0 position: 17, binding name: TO_LAYER
[00:00:25.149,993] <dbg> zmk.to_keymap_binding_released: position 17 layer 1
[00:00:25.820,587] <dbg> zmk.kscan_gpio_read_0: Sending event at 5,13 state on
[00:00:25.820,617] <dbg> zmk.zmk_kscan_process_msgq: Row: 5, col: 13, position: 17, pressed: true

[00:00:25.820,648] <dbg> zmk.position_state_changed_listener: 17 bubble (no undecided hold_tap active)
[00:00:25.820,678] <dbg> zmk.zmk_event_manager_handle_from: Listener captured the event
[00:00:25.924,987] <dbg> zmk.zmk_keymap_apply_position_state: layer: 1 position: 17, binding name: TO_LAYER
[00:00:25.925,018] <dbg> zmk.to_keymap_binding_pressed: position 17 layer 2
[00:00:25.925,018] <dbg> zmk.set_layer_state: layer_changed: layer 1 state 0
[00:00:25.925,048] <dbg> zmk.layer_event_listener: *****zmk_layer_state_changed listener: 1 0
[00:00:25.925,079] <dbg> zmk.set_layer_state: layer_changed: layer 2 state 1
[00:00:25.925,109] <dbg> zmk.layer_event_listener: *****zmk_layer_state_changed listener: 2 1
[00:00:26.433,197] <dbg> zmk.kscan_gpio_read_0: Sending event at 5,13 state off
[00:00:26.433,288] <dbg> zmk.zmk_kscan_process_msgq: Row: 5, col: 13, position: 17, pressed: false

[00:00:26.433,319] <dbg> zmk.position_state_changed_listener: 17 bubble (no undecided hold_tap active)
[00:00:26.433,319] <dbg> zmk.zmk_keymap_apply_position_state: layer: 1 position: 17, binding name: TO_LAYER
[00:00:26.433,380] <dbg> zmk.to_keymap_binding_released: position 17 layer 2
[00:00:26.623,748] <dbg> zmk.kscan_gpio_read_0: Sending event at 5,13 state on
[00:00:26.623,779] <dbg> zmk.zmk_kscan_process_msgq: Row: 5, col: 13, position: 17, pressed: true

[00:00:26.623,809] <dbg> zmk.position_state_changed_listener: 17 bubble (no undecided hold_tap active)
[00:00:26.623,840] <dbg> zmk.zmk_event_manager_handle_from: Listener captured the event
[00:00:26.728,240] <dbg> zmk.zmk_keymap_apply_position_state: layer: 2 position: 17, binding name: TO_LAYER
[00:00:26.728,302] <dbg> zmk.to_keymap_binding_pressed: position 17 layer 3
[00:00:26.728,302] <dbg> zmk.set_layer_state: layer_changed: layer 2 state 0
[00:00:26.728,332] <dbg> zmk.layer_event_listener: *****zmk_layer_state_changed listener: 2 0
[00:00:26.728,332] <dbg> zmk.set_layer_state: layer_changed: layer 3 state 1
[00:00:26.728,363] <dbg> zmk.layer_event_listener: *****zmk_layer_state_changed listener: 3 1
[00:00:27.236,450] <dbg> zmk.kscan_gpio_read_0: Sending event at 5,13 state off
[00:00:27.236,541] <dbg> zmk.zmk_kscan_process_msgq: Row: 5, col: 13, position: 17, pressed: false

[00:00:27.236,572] <dbg> zmk.position_state_changed_listener: 17 bubble (no undecided hold_tap active)
[00:00:27.236,602] <dbg> zmk.zmk_keymap_apply_position_state: layer: 2 position: 17, binding name: TO_LAYER
[00:00:27.236,633] <dbg> zmk.to_keymap_binding_released: position 17 layer 3
[00:00:27.600,219] <dbg> zmk.kscan_gpio_read_0: Sending event at 5,13 state on
[00:00:27.600,250] <dbg> zmk.zmk_kscan_process_msgq: Row: 5, col: 13, position: 17, pressed: true

[00:00:27.600,280] <dbg> zmk.position_state_changed_listener: 17 bubble (no undecided hold_tap active)
[00:00:27.600,311] <dbg> zmk.zmk_event_manager_handle_from: Listener captured the event
[00:00:27.704,528] <dbg> zmk.zmk_keymap_apply_position_state: layer: 3 position: 17, binding name: TO_LAYER
[00:00:27.704,589] <dbg> zmk.to_keymap_binding_pressed: position 17 layer 0
[00:00:27.704,589] <dbg> zmk.set_layer_state: layer_changed: layer 3 state 0
[00:00:27.704,620] <dbg> zmk.layer_event_listener: *****zmk_layer_state_changed listener: 3 0
[00:00:27.751,647] <dbg> zmk.kscan_gpio_read_0: Sending event at 5,13 state off
[00:00:27.751,800] <dbg> zmk.zmk_kscan_process_msgq: Row: 5, col: 13, position: 17, pressed: false

[00:00:27.751,831] <dbg> zmk.position_state_changed_listener: 17 bubble (no undecided hold_tap active)
[00:00:27.751,861] <dbg> zmk.zmk_keymap_apply_position_state: layer: 3 position: 17, binding name: TO_LAYER
[00:00:27.751,892] <dbg> zmk.to_keymap_binding_released: position 17 layer 0