fix(combos): Check each combo key, not just last

The current combo completion check only makes sure the last key in the
combo is set. This works when the combo is typed correctly initially, or
when reraising events in a combo of length two. However, it fails for
longer combos since the last event in pressed_keys might be set, but the
first (or subsequent) event in pressed_keys can be NULL thanks to
release_pressed_keys.

Also added a regression test.

app/src/combo.c

@@ -188,8 +188,15 @@ static int64_t first_candidate_timeout() {
 static inline bool candidate_is_completely_pressed(struct combo_cfg *candidate) {
     // this code assumes set(pressed_keys) <= set(candidate->key_positions)
     // this invariant is enforced by filter_candidates
-    // the only thing we need to do is check if len(pressed_keys) == len(combo->key_positions)
+    // since events may have been reraised after clearing one or more slots at
-    return pressed_keys[candidate->key_position_len - 1] != NULL;
+    // the start of pressed_keys (see: release_pressed_keys), we have to check
+    // that each key needed to trigger the combo was pressed, not just the last.
+    for (int i = 0; i < candidate->key_position_len; i++) {
+        if (pressed_keys[i] == NULL) {
+            return false;
+        }
+    }
+    return true;
 }
 
 static int cleanup();

app/tests/combo/press-release-long-combo-wrong-last-key/events.patterns

@@ -0,0 +1 @@
+s/.*hid_listener_keycode_//p

app/tests/combo/press-release-long-combo-wrong-last-key/keycode_events.snapshot

@@ -0,0 +1,6 @@
+pressed: usage_page 0x07 keycode 0x04 implicit_mods 0x00 explicit_mods 0x00
+pressed: usage_page 0x07 keycode 0x05 implicit_mods 0x00 explicit_mods 0x00
+pressed: usage_page 0x07 keycode 0x07 implicit_mods 0x00 explicit_mods 0x00
+released: usage_page 0x07 keycode 0x07 implicit_mods 0x00 explicit_mods 0x00
+released: usage_page 0x07 keycode 0x05 implicit_mods 0x00 explicit_mods 0x00
+released: usage_page 0x07 keycode 0x04 implicit_mods 0x00 explicit_mods 0x00

app/tests/combo/press-release-long-combo-wrong-last-key/native_posix.keymap

@@ -0,0 +1,37 @@
+#include <dt-bindings/zmk/keys.h>
+#include <behaviors.dtsi>
+#include <dt-bindings/zmk/kscan-mock.h>
+
+/ {
+	combos {
+		compatible = "zmk,combos";
+		combo_one {
+			timeout-ms = <80>;
+			key-positions = <0 1 2>;
+			bindings = <&kp Z>;
+		};
+	};
+
+	keymap {
+		compatible = "zmk,keymap";
+		label ="Default keymap";
+
+		default_layer {
+			bindings = <
+				&kp A &kp B
+				&kp C &kp D
+			>;
+		};
+	};
+};
+
+&kscan {
+	events = <
+		ZMK_MOCK_PRESS(0,0,10)
+		ZMK_MOCK_PRESS(0,1,10)
+		ZMK_MOCK_PRESS(1,1,10)
+		ZMK_MOCK_RELEASE(1,1,100)
+		ZMK_MOCK_RELEASE(0,1,100)
+		ZMK_MOCK_RELEASE(0,0,100)
+	>;
+};