catch crossover bilateral combinations with timeout

docs/tap_hold.md

@@ -211,6 +211,12 @@ To delay the registration of modifiers (such as `KC_LGUI` and `KC_RGUI`, which a
 DEFERRED_EXEC_ENABLE = yes
 ```
 
+To enable *crossover* bilateral combinations (which start on one side of the keyboard and cross over to the other side, such as `RSFT_T(KC_J)` and `LGUI_T(KC_A)` in the word "jam"), add the following line to your `config.h` and define a value: hold times greater than that value will permit crossover bilateral combinations.  For example, if you typed `RSFT_T(KC_J)` and `LGUI_T(KC_A)` faster than the defined value, the keys `KC_J` and `KC_A` would be sent to the computer.  In contrast, if you typed slower than the defined value, the keys `RSFT(KC_A)` would be sent to the computer.
+
+```c
+#define BILATERAL_COMBINATIONS_CROSSOVER 75
+```
+
 To monitor activations in the background, enable debugging, enable the console, enable terminal bell, add `#define DEBUG_ACTION` to `config.h`, and use something like the following shell command line:
 
 ```sh

tmk_core/common/action.c

@@ -47,7 +47,7 @@ int retro_tapping_counter = 0;
 #    include <fauxclicky.h>
 #endif
 
-#if (BILATERAL_COMBINATIONS + 0)
+#if (BILATERAL_COMBINATIONS + BILATERAL_COMBINATIONS_CROSSOVER + 0)
 #    include "quantum.h"
 #endif
 
@@ -231,7 +231,7 @@ static struct {
     uint8_t tap;
     uint8_t mods;
     bool left;
-#    if (BILATERAL_COMBINATIONS + 0)
+#    if (BILATERAL_COMBINATIONS + BILATERAL_COMBINATIONS_CROSSOVER + 0)
     uint16_t time;
 #    endif
 #    if (BILATERAL_COMBINATIONS_DEFERMODS + 0)
@@ -267,7 +267,7 @@ static void bilateral_combinations_hold(action_t action, keyevent_t event) {
     bilateral_combinations.tap = action.layer_tap.code;
     bilateral_combinations.mods = (action.kind.id == ACT_LMODS_TAP) ? action.key.mods : action.key.mods << 4;
     bilateral_combinations.left = bilateral_combinations_left(event.key);
-#    if (BILATERAL_COMBINATIONS + 0)
+#    if (BILATERAL_COMBINATIONS + BILATERAL_COMBINATIONS_CROSSOVER + 0)
     bilateral_combinations.time = event.time;
 #    endif
 #    if (BILATERAL_COMBINATIONS_DEFERMODS + 0)
@@ -304,6 +304,18 @@ static void bilateral_combinations_tap(keyevent_t event) {
             unregister_mods(bilateral_combinations.mods);
             tap_code(bilateral_combinations.tap);
         }
+#    if (BILATERAL_COMBINATIONS_CROSSOVER + 0)
+        else {
+            if (TIMER_DIFF_16(event.time, bilateral_combinations.time) > BILATERAL_COMBINATIONS_CROSSOVER) {
+                dprint("BILATERAL_COMBINATIONS_CROSSOVER: timeout\n");
+                bilateral_combinations_clear();
+                return;
+            }
+            dprint("BILATERAL_COMBINATIONS_CROSSOVER: change\n");
+            unregister_mods(bilateral_combinations.mods);
+            tap_code(bilateral_combinations.tap);
+        }
+#    endif
         bilateral_combinations_clear();
     }
 }